# All events

June 1st, 2015 - **Workshop "Geometric Invariants and Spectral Curves"**

On June 1-5 there is a workshop "Geometric Invariants and Spectral Curves" at the Lorentz Center, Leiden. Part of this workshop is specially targeted for PhD students. Everybody is welcome!

May 26th, 2015 - **Workshop on mathematical physics**

On May 26-28 there is a workshop on mathematical physics at the University of Amsterdam. Everybody is welcome!

March 12th, 2015 - **Mini-Workshop on Symplectic Geometry, Universiteit Utrecht**

This mini-workshop is aimed at researchers, Ph.D. students, and advanced master's students working in symplectic geometry and related areas. It is organized jointly with the Vrije Universiteit Amsterdam.

This is the first instance of what we plan to make a biannual tradition. The goal of these mini-workshops is to strengthen the symplectic community of the Netherlands and to connect it with abroad. Topics will include Hamiltonian dynamics, the symplectic embedding question, holomorphic curves, and Floer homology.

**Speakers**

Kai Cieliebak (Universität Augsburg)

Felix Schlenk (Université de Neuchâtel)

Rob van der Vorst (Vrije Universiteit Amsterdam)

Frol Zapolski (University of Haifa)

**Organizers**

Oliver Fabert (Vrije Universiteit Amsterdam)

Fabian Ziltener (Universiteit Utrecht)

For any questions please contact Oliver Fabert at o.fabert ``at'' vu.nl and Fabian Ziltener at f.ziltener ``at'' uu.nl .

This mini-workshop is supported by the Universiteit Utrecht, the Vrije Universiteit Amsterdam, and the Geometry and Quantum Theory Cluster.

February 13th, 2015 - **Workshop on Algebraic Geometry**

November 14th, 2014 - **GQT Graduate School and Colloquium**

3 - 5 Novmber 2014: GQT graduate school

6 - 7 November 2014: GQT Colloquium

location: NH Zandvoort, Zandvoort

website: GQT colloquium

The school will focus on three topics:

- Maarten Solleveld: p-adic groups (3 Nov)

- Jasper Stokman: Quantum integrable systems (4 Nov)

- Andre Henriques: K-theory (5 Nov)

The colloquium will consist of several talks related to the topics discussed during the school as well as some talks on general GQT themes. For details, visit the event's webpage.

Both events are aimed primarily at GQT-members, with the school aiming especially at PhD-students.

July 7th, 2014 - **Integrability and Isomonodromy in Mathematical Physics
**

A workshop at the Lorentz Center. More information to follow.

July 2nd, 2014 - **GQT Graduate School and Colloquium**

30 June - 2 July 2014: GQT graduate school

3 - 4 July 2014: GQT Colloquium

location: Woudschouten conference center, near Zeist

website: http://www.projects.science.uu.nl/GQT/GQT_colloquium

The school will focus on three topics:

- Raf Bocklandt: Mirror symmetry

- Carel Faber: Gromov-Witten invariants in algebraic geometry

- Ben Moonen: Hodge structures

The colloquium will consist of several talks related to the topics discussed during the school as well as some talks on general GQT themes. The speakers are:

Chris Peters, Jozef Steenbrink, Barbara Fantechi, Tom Coates, Silvia Sabatini, Nathalie Wahl, Ed Segal, Mingmin Shen and Stefan Vandoren.

Both events are aimed primarily at GQT-members, with the school aiming especially at PhD-students.

June 19th, 2014 - **Higher Geometric Structures along the Lower Rhine V**

**Speakers**

Larry Breen (Paris 13)

Yonatan Harpaz (Nijmegen)

Ralph Kaufmann (Purdue and MPIM)

Pascal Lambrechts (Louvain-la-Neuve)

Silvia Sabatini(Lisbon)

Urs Schreiber (Nijmegen)

Daniele Sepe (Utrecht)

Participation is free, but registration is necessary for the obvious logistic reasons. For further information, see

http://www.ru.nl/math/research/vmconferences/2014-higher/

June 16th, 2014 - **Workshop on Instanton Counting: Moduli Spaces, Representation Theory and Integrable Systems**

Over the last 30 years there have been remarkable instances where physical theories provided a formidable input to mathematicians, off ering the stimulus to the creation of new mathematical theories, and supplying strong evidence for highly nontrivial theorems. An example of this kind of interaction between mathematics and physics is gauge theory, and, in particular, instanton counting. This refers to the study of the relevant partition functions (such as the Nekrasov partition functions) in gauge theory by using an algebro-geometric approach, and is related to some highly nontrivial mathematical problems (such as the Alday- Gaiotto-Tachikawa conjecture) which come from physical issues in gauge and conformal field theory.

This workshop aims at assessing the state of the art in this area of research in its various aspects. In particular, it focuses on various aspects of the geometry of the moduli spaces of framed sheaves and of Nakajima quiver varieties, of their relations to integrable systems, of the instanton counting on toric surfaces and of the AGT conjecture. We believe that a more fruitful interaction between the different communities of people working in these fields will strengthen them individually and collectively.

Invited speakers:
Alexander Belavin,
Mikhail Bershtein,
Alexander Braverman,
Erik Carlsson,
Duiliu Emanuel Diaconescu,
Michael Finkelberg,
Evgeny Gorsky,
Weiping Li,
Hiraku Nakajima,
Mattia Pedrini,
Rubik Poghosyan,
Giulia Saccà,
Justin Sawon,
Richard J. Szabo,
Alessandro Tanzini,
Eric Vasserot,
Niclas Wyllard

For more information and registration please go to the web-page of the Lorentz Center.

May 20th, 2014 - **Workshop "Knots and Physics" **

On May 20-21, 2014, we have a workshop "Knots and Physics" on the occasion of the thesis defense of Alexey Sleptsov. The speakers are A. Brini, V. Dolotin, E. Gorsky, A. Mironov, A. Morozov, J. Rasmussen, A. Sleptsov, P. Sulkowski, and P. Zinn-Justin.

The schedule, titles and abstracts are available at the following link:

http://staff.science.uva.nl/~sshadrin/knotsandphysics.html

Everybody is welcome!

March 18th, 2014 - **IMAPP Colloquium Alain Connes, Radboud University Nijmegen**

Title: 'The spectral model of particle physics'
Time: 16:00
Place: Radboud University Nijmegen - Huygensgebouw HG00.304

February 13th, 2014 - **4th workshop Higher Geometric Structures along the Lower Rhine**

Announcing the fourth workshop of the series "Higher Geometric Structures along the Lower Rhine", jointly organized by the Geometry/Topology groups in Bonn, Nijmegen, and Utrecht. This meeting will be held at the Max Planck Institute for Mathematics in Bonn on February 13-14, 2014.

**Speakers**

Dimitri Ara (Nijmegen)

Michael Batanin (Macquarie University, Sydney/MPIM)

Pedro Frejlich (Utrecht)

Bas Janssens (Utrecht)

Martin Markl (Prague/MPIM)

Eckhard Meinrenken (University of Toronto)

Matan Prezma (Nijmegen)

For registration and more information please visit the website: http://www.mpim-bonn.mpg.de/node/5119

January 30th, 2014 - **Conference: The geometry of special functions**

A two-day conference in Nijmegen, 30--31 January 2014

** Speakers: **

Masaaki Yoshida (Kyushu University, Fukuoka)

Daniel Allcock (University of Texas, Austin)

Duco van Straten (Johannes Gutenberg Universität Mainz)

Michele Vergne (Institut de Mathématiques de Jussieu, Paris)

Michel Duflo (Institut de Mathématiques de Jussieu, Paris)

Jasper Stokman (Universiteit van Amsterdam and Radboud Universiteit Nijmegen)

Jan Stienstra (Universiteit Utrecht)

Frits Beukers (Universiteit Utrecht)

** Organisers: **

Eduard Looijenga, Eric Opdam and Maarten Solleveld

January 23rd, 2014 - **Workshop "Moduli of curves and mathematical physics"**

On the occasion of the thesis defense of Loek Spitz, a workshop takes place on Thursday, January 23, 2014 at the University of Amsterdam (Plantage Muidergracht 24,
1018 TV Amsterdam, N.B.: This is OLD LOCATION of the KdV Institute). The lecture room is P0.18.

The program is as follows:

14:00-15:00 Alessandro Chiodo (Paris): Applications of quantum theories of Landau-Ginzburg models

15:00-15:15 Break.

15:15-16:15 Dimitri Zvonkine (Paris): The Chern character of the Verlinde bundle

16:15-16:30 Break.

16:30-17:30 Motohico Mulase (Davis): Quantum curves for Hitchin fibrations

Abstract Chiodo: Landau-Ginzburg models are singularities of the form f:X->B
arising for instance as mirror partners of several Fano manifolds.
More precisely, we consider mirror symmetry as an identification of
two local systems. The first local system is classical in algebraic
geometry and encodes the cohomology of the fibres of f:X->B. The
second local system embodies quantum periods of the Fano manifold and
arises from Gromov-Witten theory. Fan-Jarvis-Ruan and
Polishchuk-Vaintrob set up analogue quantum theories applying also to
Landau-Ginzburg models and allow us to cast mirror symmetry in a
global, more flexible, framework. In this way some well known
obstacles in Gromov-Witten theory become more approachable. In
particular we will illustrate "non-convexity" and "non-concavity",
which are some of the main outstanding obstacles preventing us from
knowing Gromov-Witten invariants in many major examples such as the
quintic threefold in higher genus. I will describe recent work by
Jérémy Guéré proving a mirror theorem relating certain Landau-Ginzburg
models without concavity.

Abstract Zvonkine: We give an explicit formula for the total Chern character of the Verlinde bundle over the moduli space of stable curves in terms of tautological classes. The Chern characters of the Verlinde bundles form a semi-simple CohFT, while their ranks, given by the Verlinde formula, form a semi-simple fusion algebra. According to the Teleman's classification of semisimple
CohFTs, there exists an element of Givental's group that transforms the fusion algebra into the CohFT. We determine this element using the first
Chern class of the Verlinde bundle on the space of smooth curves, and the projective flatness of the Hitchin connection.

(Joint with A. Marian, D. Oprea, R. Pandharipande, A. Pixton)

Abstract Mulase: The quantum curves for SL(2)-Hitchin fibrations were
constructed in October 2013 in a joint paper with Olivia Dumitrescu. In
this talk we discuss two most recent topics in this direction of
research: one is the action of the monodromy group of the Hitchin
fibration on the family of quantum curves, and the other is a
generalization of the theory to parabolic Hitchin fibrations. This
research is motivated by understanding the AGT correspondence from the
point of view of quantum curves.

The talk is based on the on-going
joint work with Dumitrescu and Laura Schaposnik.

The defence of Loek Spitz will take place on 10:00 the same day at the Agnietenkapel (Oudezijds Voorburgwal 229-231, 1012 EZ Amsterdam). Title of the thesis: "Hurwitz numbers, moduli of curves, topological recursion, Givental's theory and their relations.".

Everybody is welcome!

January 14th, 2014 - **GQT Graduate School and Colloquium**

The first GQT Graduate School (14-16 Jan) and Colloquium (17-18 Jan) will take place at Woudschoten conference center in Zeist.

Tutorials during the school:

- Klaas Landsman: What is noncommutative geometry?
- Hessel Posthuma: What is index theory?
- Fabian Ziltener: What is Gromov-Witten theory?

Confirmed speakers for the colloquium: Peter Albers (Muenster); Alessandro Chiodo (Jussieu); Xin Li (Queen Mary); Richard Sharp (Warwick); more to follow.

For information on registration, schedule and more see the event's webpage.

December 17th, 2013 - **Workshop on Algebraic Cycles and Tautological classes**

Tuesday the 17th and Wednesday the 18th of December on the occasion of Qizheng Yin's defence of his doctors thesis.

The defence will be on the Wednesday.

**Speakers (December 17th)**

Gerard van der Geer (Amsterdam)

Dan Petersen (Zürich)

Arnaud Beauville (Nice)

Qizheng Yin (Nijmegen)

**Speakers (December 18th)**

Lenny Taelman (Leiden)

Claire Voisin (École Polytechnique)

Sergey Shadrin (Amsterdam)

November 22nd, 2013 - **Belgian-Dutch Algebraic Geometry Day**

**Venue**

The lectures are given in the Huygens Building, room HG00.071 on the ground floor.

Address: Heyendaalseweg 135, Nijmegen.

**Programme**

13:00-14:00 Nero Budur (Leuven) TBA

14:00-14:30 Coffee break

14:30-15:30 Stefan Schröer (Düsseldorf) TBA

15:30-16:00 Coffee break

16:00-17:00 René Schoof (Rome) TBA

As usual, after the lectures we intend to go for an informal dinner in town.

November 21st, 2013 - **Workshop on Foliations and Orbispaces, 21-22 November**

**Description**

The focus of this short workshop lies on (possibly
singular) foliations are their leaf spaces, both from
a classical perspective (\Gamma-structures,
Riemannian foliations,..) and a modern one (Lie
groupoids).

**Speakers**

Gael Meignez (Bretagne-Sud)

Marcos Alexandrino (Sao Paulo)

Hessel Posthuma (Amsterdam)

Matias del Hoyo (Utrecht)

Marco Zambon (Madrid)

October 17th, 2013 - **Higher Geometric Structures along the Lower Rhine III**

This is the third in a series of short workshops jointly organized by the Geometry/Topology groups in Bonn, Nijmegen, and Utrecht, all situated along the Lower Rhine. The focus lies on the development and application of new structures in geometry and topology such as Lie groupoids, differentiable stacks, Lie algebroids, generalized complex geometry, topological quantum field theories, higher categories, homotopy algebraic structures, higher operads, derived categories, and related topics. The first workshop took place in Bonn and the second in Nijmegen.

**Speakers **

Camilo Arias Abad (Bonn)

Javier Gutiérrez (Nijmegen)

Matias del Hoyo (Utrecht)

Arturo Prat-Waldron (Bonn)

Gregor Schaumann (Universität Erlangen-Nürnberg)

Pavol Ševera (Université de Genève)

Anton Zeitlin (Columbia University)

October 14th, 2013 - **Workshop Noncommutative Geometry and Particle Physics, Leiden**

Lorentz Center Leiden, October 14-18, 2013.

**Topics:**

**Scientific organizers:**

September 27th, 2013 - **Workshop Knots & Physics, Amsterdam**

**Speakers:**

Gaetan Borot (MPI Bonn),

Jinseok Cho (KIAS Seoul),

Sebas Eliens (ITF Amsterdam),

Hitoshi Murakami (Tohoku University),

Satoshi Nawata (NIKHEF Amsterdam).

**Organisers:** Satoshi Nawata and Roland van der Veen

July 15th, 2013 - **Workshop "Elliptic Integrable Systems and Hypergeometric Functions"**

5 day workshop from July 15th - 19th, 2013.
Scientific organizers: Erik Koelink, Masatoshi Noumi, Eric Rains, Hjalmar Rosengren, Simon Ruijsenaars, Jasper Stokman.

June 27th, 2013 - **A singular life - Conference in honour of Eduard Looijenga**

This two-day conference (27 & 28 of June) marks the retirement of Professor Eduard Looijenga and will be a celebration of his achievements and influence in Dutch and International mathematics. The confirmed speakers are
Arnaud Beauville (Laboratoire J.-A. Dieudonné, Nice),
Igor Dolgachev (University of Michingan),
Carel Faber (Royal Institute of Technology, Stockholm),
Gerard van der Geer (University of Amsterdam),
Gert Heckman (Radboud Universiteit Nijmegen),
Joseph Steenbrink (Radboud Universiteit Nijmegen),
Jonathan Wahl (University of North Carolina),
Shing-Tung Yau (Harvard University)
Don Zagier (Max Planck Institute -- Bonn)

June 21st, 2013 - **G&T day - Utrecht**

The Quarterly seminar on Topology and Geometry aims to take place every bimester in the mathematics department in Utrecht. Our next meeting will happen on the 21st of June 2013 in MIN 211.

The speakers will be Jonny Evans, Igor Khavkine and James Tener.

June 5th, 2013 - **Mini Workshop on locally analytic representations and some applications**

June 5-6, 2013, at Vrije Universiteit Amsterdam

supported by the DIAMANT cluster*

**Organizers:** Deepam Patel (VU Amsterdam), Tobias Schmidt (Munster), Matthias Strauch (Indiana)

* funded by the Netherlands Organisation for Scientific Research (NWO), the Ministry of Education, Culture and Science (OCW), and the Ministry of Economic Affairs (EZ).

May 23rd, 2013 - **Topology & Geometry Day on the occasion of Maria Amelia Salazar's Ph.D. defense**

May 17th, 2013 - **GQT colloquium Utrecht**

Place: Universiteit Utrecht; Minnaert Building, room 208.

Schedule:

13:00 to 14:00 - Kim Froyshov (Aarhus): On the existence of representations of finitely presented groups in compact Lie groups;

14:00 to 14:30 - Coffee;

14:30 to 15:30 - Moritz Groth (Nijmegen): Some first steps with Grothendieck derivators;

15:45 to 16:45 - Matthias Kreck (Hausdorff Institute): Special codes - special manifolds?

April 26th, 2013 - **Workshop "Moduli of curves and integrable hierarchies"**

On the occasion of the thesis defense of Alexandr Buryak, a workshop takes place on Friday, April 26 at the University of Amsterdam (Plantage Muidergracht 24,
1018 TV Amsterdam, N.B.: This is OLD LOCATION of the KdV Institute). The lecture room is P0.14.

The program is as follows:

13:15-14:15 Maxim Kazarian (Moscow): Topological recursion for the genus zero descendant Hurwitz potential.

14:15-14:45 Coffee and tee.

14:45-15:45 Johan van de Leur (Utrecht): Hirota equations for the extended bigraded Toda hierarchy
and the total descendant potential of CP^1 orbifolds.

16:00-17:00 Dimitri Zvonkine (Paris): A (complete?) family of relations between tautological cohomology
classes of Mbar_{g,n}

Abstract Kazarian: Double Hurwitz numbers enumerate possible ways to represent the identical
permutation as the product of two permutations of given cyclic types and
a given number of transpositions. In topological terms, they describe
topologically distinct meromorphic functions on Riemann surfaces of given
genus with prescribed critical values and prescribed orders of poles and
zeroes. These numbers themselves are well studied and there are known
formulas for their generating function. In spite of the existence of such
formulas and a variety of modern proofs, many natural questions concerning
these numbers remain open.

We propose a new recursion for these numbers that has a topological origin:
it is derived from cohomological information contained in the stratification
of the Hurwitz space by multisingularities of the functions. We expect that
variations of this approach could be adopted to other families of Hurwitz
numbers for which closed formulas are not known at the moment, including
those for curves of higher genera.

(Joint work with S.Lando and D.Zvonkine)

Abstract van de Leur: Milanov and Tseng conjectured that the total descendent potential of the orbifold C_{k;m} is a tau function of the extended bigraded Toda hierarchy.
We prove this conjecture.

(Joined work with Guido Carlet)

Abstract Zvonkine: Let M_g be the moduli space of smooth curves of genus g. As g
tends to infinity, the cohomology ring of M_g stabilizes to
Q[kappa_1, kappa_2, ...] for certain natural cohomology classes
kappa_m. For a fixed g, however, there are polynomial relations
between the kappa-classes. The study of these relations was started
by C. Faber in 1993 and is still not finished 20 years later.

We can complicate the problem by adding marked points and passing to
the Deligne-Mumford compactification of the moduli space, which
greatly increases the number of generators and relations. We will
construct a family of relations between these generators that contains
all known relations and, conjecturally, all existing relations. The
construction involves r-spin structures (r-spin = r-th root of the
cotangent line bundle to the curve) and Frobenius manifolds.

(Joint work with A. Pixton et R. Pandharipande)

The defence of Alexandr Buryak will take place on 10:00 at the Agnietenkapel (Oudezijds Voorburgwal 229-231, 1012 EZ Amsterdam). Title of the thesis: "Topology of the moduli space of curves
and integrable hierarchies".

Everybody is welcome!

March 28th, 2013 - **Operations on Hochschild complexes, revisited**

**Speaker:** Boris Tsygan (Northwestern University)

**Date and time:** Thursday, March 28th, 2013 from 16:00-17:00hrs

**Location:** UVA, Science Park 904, Room A1.06

**Title:** Operations on Hochschild complexes, revisited.

**Abstract:** Algebraic structures on Hochschild cochain and chain complexes of algebras are long known to be of considerable interest. On the one hand, some of them arise as standard operations in homological algebra. On the other hand, for the ring of functions on a manifold, Hochschild homology, resp. cohomology, is isomorphic to the space of differential forms, resp. multivector fields, and many algebraic structures from classical calculus can be defined (in a highly nontrivial way) in a more general setting of an arbitrary algebra and its Hochschild complexes. Despite an extensive amount of work on the subject, it appears that large parts of the algebraic structure on the Hochschild complexes of algebras and their tensor products are still unknown. I will review the known results (Kontsevich-Soibelman, Dolgushev, Tamarkin and myself, Keller) and then outline some provisional results and conjectures about new operations. The talk will not assume any prior knowledge beyond basic facts about complexes and (co)homology.

March 1st, 2013 - **GQT colloquium Nijmegen**

place: Radboud Universiteit Nijmegen, Huygensgebouw

time: 13:00 - 17:00

room: HG00.108

program:

13:00 - 14:00 ** Christian Voigt ** (University of Glasgow)

** The string group and vertex algebras **

The string group String(n) is an infinite dimensional analogue of the spin group Spin(n) familiar
from geometry and index theory. In this talk I will discuss a tentative realisation of String(n) using unitary
vertex superalgebras and field algebras. This includes a categorified analogue of the Clifford algebra and its
spinor representation, and I will explain carefully the analogy to the situation for the spin group.

14:30 - 15:30 ** Simon Salamon ** (King's College London)

** Surveying points in the complex projective plane **

I shall introduce Zauner's conjecture on the existence of
SIC-POVM's (symmetric informationally complete positive operator valued
measures, that correspond to n^2 equidistant points in CP^(n-1) with the
Fubini-Study metric). The theory will be illustrated in only the
simplest situations of n=3 and 4, but from a geometer's perspective
using the concept of moment mapping.

16:00 - 17:00 ** Raf Bocklandt ** (Universiteit van Amsterdam)

** Noncommutative mirror symmetry for punctured surfaces **

A dimer model on a surface with punctures is an oriented graph such that
its nodes correspond to the punctures and the arrows circle round
the faces they cut out. To any dimer model Q we can associate 2
categories: A wrapped Fukaya category F(Q) and a category of matrix
factorizations M(Q).

In both categories the objects are arrows, which are interpreted as
Lagrangian subvarieties in F(Q) and will give us certain matrix
factorizations of a potential on the Jacobi algebra of the dimer in
M(Q).

We show that there is a duality D on the set of all dimers such that
for consistent dimers the category of matrix factorizations M(Q) is
isomorphic to the Fukaya category of its dual, F(D(Q)). We also
discuss the connection between classical mirror symmetry.

December 18th, 2012 - **Workshop Special Functions and Lie Theory**

Speakers: Alberto Grunbaum (UC Berkeley, USA), Paul-Emile Paradan (Montpellier 2, Fr), Pablo Roman (U Nacional Cordoba, Arg), Jasper Stokman (UvA/RU), Wolter Groenevelt (TUD) and Maarten van Pruijssen (RU).
PhD-defense of Maarten van Pruijssen on December 19, 2012, 10.30.

December 6th, 2012 - **2 day seminar - Higher Geometric Structures along the Lower Rhine
**

This second meeting of the seminar, jointly organised by Bonn (MPI), Nijmegen, and Utrecht, will be held in Nijmegen on December 6th and 7th 2012.

November 16th, 2012 - **GQT colloquium Amsterdam**

place: Universiteit van Amsterdam, Science Park

time: 13:30 - 17:00

Room G5.29

13.30-14.30 Oscar Randal-Williams (University of Cambridge): The "Mumford conjecture" package, and applications

14.30-15.00 Coffee break

Room F1.02

15.00-16.00 Daniel Huybrechts (Universität Bonn): Old and new problems in the theory of K3 surfaces

16.15-17.15 Geordie Williamson (Max Planck Institut Bonn): Coxeter groups, Kazhdan-Lusztig polynomials and a little Hodge theory

Abstract Randal-Williams:

I will describe how recent work inspired by Madsen and Weiss' proof of
Mumford's conjecture (on the stable cohomology of the moduli space of
Riemann surfaces) gives a conceptual and computational understanding
of moduli spaces of Riemann surfaces with extra structure.
In particular, I will focus on two interesting examples: the moduli
spaces of r-Spin Riemann surfaces, and the universal Picard variety
over $M_g$. I will then explain how studying the universal Picard
variety leads to a new method for producing tautological relations
among the $\kappa_i$ on $M_g$.

Abstract Huybrechts:

In this talk I will survey a few questions that
have been studied intensively for K3 surfaces over the
last years. In particular, I will mention rational curves
and rational points on K3 surfaces, as well as algebraic
cycles and derived categories.

Abstract Williamson:

In 1979 Kazhdan and Lusztig described a remarkably simple
yet baffling algorithm to associate a polynomial to any pair of
elements in a Coxeter group. Nowadays Kazhdan-Lusztig polynomials play
a central role in Lie theory. In this talk I will discuss Coxeter
groups and their geometry and describe Kazhdan and Lusztig's
algorithm. I will then discuss some recent work with Ben Elias where
we use some ideas from Hodge theory to try to understand these
polynomials.

October 8th, 2012 - **seminar Elliptic Integrable Systems and Hypergeometric Functions **

Subjects:
1. Elliptic hypergeometric functions
2. Elliptic quantum groups
3. Elliptic integrable lattice models
and their interplay.
Preparatory seminar for the Lorentz workshop Elliptic Integrable Systems and Hypergeometric Functions (15-19 July 2013).
(Tentative) dates: 8/10, 22/10, 12/11, 19/11, 3/12, 17/12 in 3012

July 3rd, 2012 - **Lectures on the unbounded Kasparov product**

Lectures on the unbounded Kasparov product by Adam Rennie (University of Wollongong)

Dates: July 3,5,12,17,19 and 26.

Time: 15:45-17:15

Place: Radboud University Nijmegen, Huygensgebouw, room HG03.632

June 27th, 2012 - **Workshop Special Functions**

One day workshop on Special Functions and related areas. Speakers: Maarten van Pruijssen (Nijmegen), Ana Martinez de los Rios (Seville), Kerstin Jordaan (Pretoria), Kenny De Commer (Cergy-Pontoise), Jasper Stokman (Amsterdam).

June 1st, 2012 - **GQT colloquium Utrecht
**

Location: Minnaert building, room 208, Universiteit Utrecht.

13.15-14.15 Jan Denef, Model theory of local fields and toroidalization of morphisms

14.30-15.30 Florian Schätz, de Rham Theorem and higher holonomies

15.30-16.00 Coffee and tea

16.00-17.00 Peter Teichner, Cohomology via field theories

17.00-18.00 Drinks in library Math building

Abstracts:

Peter Teichner, Cohomology via field theories

We'll present results with Stephan Stolz on new relations between algebraic topology and physically motivated notions of field theories.

Jan Denef, Model theory of local fields and toroidalization of morphisms

This talk is about new proofs of some old but celebrated results in the model theory of henselian valued fields. A key example is the Ax-Kochen-Ersov transfer principle that for a given "elementary" assertion about rings we have the following for almost all primes p: the assertion is true in the ring of p-adic integers if and only if it is true in the ring of formal power series over the field with p elements. In the talk we will give an easy proof of this and related results, using a deep result in algebraic geometry, namely the theorem of Abramovich and Karu on toroidalization of morphisms.

Florian Schätz, de Rham Theorem and higher holonomies

I will first sketch an extension of de Rham's Theorem to an homotopy equivalence of differential graded algebras. This extension allows one to define higher holonomies for graded connections. Then I will indicate how one might use these higher holonomies in order to generalize Tamarkin's approch to the formality of the little disks operad to higher dimensions (this result was established by Kontsevich via a different approach). The last part is joint work in progress with C. Arias Abad.

March 29th, 2012 - **Workshop Quantum Groups**

There is a one-day workshop Quantum Groups on Thursday, March 29, 2012
with speakers: Martijn Caspers (Radboud U), Kenny De Commer (U Cergy
Pontoise, France), Thomas Timmermann (WWU Münster, Germany), Alfons Van
Daele (KU Leuven, Belgium).

March 19th, 2012 - **Workshop "Noncommutative algebraic geometry and its applications to physics"**

Topics include: Noncommutative Algebraic and Differential Geometry; Categorical Noncommutative Algebraic Geometry; Moduli Spaces in Noncommutative Geometry; Noncommutative Geometry,
and Representation Theory; Applications to String Theory and Quantum Field Theory

Speakers include Yuri Berest, Simon Brain, Lucio Cirio, Alexander Gorsky, Dmitry Kaledin, Ralph Kaufmann, Ludmil Katzarkov, Sebastian Klein, Lieven le Bruyn, Alexander Kuznetsov, Matilde Marcolli, Dmitry Orlov, Goncalo Tabuada, Paul Smith, Vladimir Sokolov, Tom Sutherland, Walter van Suijlekom, Richard Szabo, Jan Jitse Venselaar

March 15th, 2012 - **Workshop Algebraic Geometry**

On the occasion of the thesis defense of Bart van den Dries, a workshop takes place on Thursday, March 15, Room 071 of the Buys-Ballot Building.

The program is as follows:

14:15-14:55 Claire Voisin (Paris): Integral Hodge classes and birational invariants.

15:05-15:55 Slava Kharlamov (Strasbourg): Abundance of real solutions in certain real enumerative problems.

16:15-16:55 Gert Heckman (Nijmegen): On the regularization of the Kepler problem.

Abstract Kharlamov: Surprisingly, in several real enumerative problems the number of real solutions happens to be comparable (for example, in logarithmic scale) with the number of complex ones. Such a phenomenon was first observed in the case of interpolation of real points on a real rational surface by real rational curves (here, the key tool is given by the Welschinger invariants, which can be seen as a real analogue of genus zero Gromov-Witten invariants). In this short talk I will illustrate the same phenomenon by counting real lines (or more generally, real linear subspaces) on nonsingular projective hypersurfaces and their intersections. The key tool in these counts is a kind of real version of Schubert calculus.

Abstract Heckman: We first explain the regularization of the Kepler problem by Moser, and show how the Ligon-Schaaf regularization can be obtained from it in simple terms, as opposed to the original calculational approach by Ligon and Schaaf, even with the simplifications by Cushman and Duistermaat.

March 2nd, 2012 - **GQT colloquium Nijmegen**

Location: Linnaeus building (Heyendaalseweg 137), room LIN 3.

Schedule:

13:00-14:00: Anton Deitmar (Tübingen)

14:00-14:15: Handing out of the GQT master thesis prize

14:30-15:30: Maarten Solleveld (Nijmegen)

15:30-16:00: Coffee/Tea

16:00-17:00: Christopher Deninger (Münster)

17:00-??: Reception

Titles and abstracts:

Anton Deitmar: Higher order invariants and non-unitary spectral theory

Symmetry is usually described as invariance under a group action.
If the group action is linear, being symmetric is equivalent to being
annihilated by the augmentation ideal of the group ring.
Higher order invariants of lattices, i.e. elements which are annihilated by
higher powers of the augmentation ideal, have in the last decade come into
focus in the theory of automorphic forms. They arise in percolation theory
and converse theorems. Spectral theory of these has two aspects: varying the
lattice via Hecke-theory leads to representations of adele groups, whereas
keeping the lattice fixed and varying the representation at the infinite
place leads to non-unitary spectral theory. The latter is in general
unworkable, but in the situation of lattices in Lie groups there is enough
structure around to feed the hope for a nice theory.

Maarten Solleveld: The p-adic Langlands correspondence for the principal series

The local Langlands program aims at the classification of all irreducible
representations of reductive groups over local fields. It was set up by
Langlands in the sixties and continues to inspire much of the research in
this field.
Its p-adic branch, also called the p-adic Langlands correspondence, remains
conjectural up to this day. It has been established in only a few cases,
most noticeably for general linear groups and for irreducible
representations in the principal series of split groups. We will discuss the
latter, where it comes from and what makes it plausible.

Christopher Deninger: Generalized Nevanlinna theory and invariant measures on the circle

It is well known that real measures on the circle are
characterized by their Herglotz transform, an analytic function in the
unit disc. Invariance of the measure under N-multiplication translates
into a functional equation for the Herglotz transform. Using elements from
the theory of Hardy spaces one gets a somewhat surprising condition for a
sequence of complex numbers to be the Fourier coefficients of an
N-invariant measure.
Next, starting from any atomless measure on the circle we construct
atomless premesures of bounded kappa-variation in the sense of Korenblum
which are invariant under s given pairwise prime integers. The relevant
function kappa is a generalized entropy function depending on s. The proof
uses Korenblum's generalized Nevanlinna theory. Passing to "kappa-singular
measures" and extending these to elements in a Grothendieck group of
possibly unbounded measures on the circle, one obtains generalized
invariant measures which are carried by "kappa-Carleson" sets. The range
of this construction depends on interesting questions about cyclicty in
growth algebras of analytic functions on the unit disc. If there is time,
we also discuss some very formal relations with Witt vectors. For example
the Artin-Hasse p-exponential "is" a p-invariant premeasure of bounded
kappa_1 variation.

January 20th, 2012 - **Mini symposium in honor of Wilberd van der Kallen **

Wilberd van der Kallen will turn 65 in January 2012.
The Mathematical Institute of the University of Utrecht and the Geometry and Quantum Theory cluster will celebrate this with a mini symposium in Wilberd's honor on January 20, 2012 from 13.00-17.00 h. in room 211 of the Minnaert building, de Uithof, Utrecht.

**Program: **

13.15-14.15:
**Prof. Jean Fasel **(Mathematisches Institut der Universität München) **Unimodular rows**

14.15-14.45: Coffee and tea

14.45-15.45: **Prof.Henning Haahr Andersen** (Department of Mathematics, University of Aarhus)
**Tilting modules for reductive algebraic groups**

16.00-17.00:**
Prof. Antoine Touzé** (Institut Galilée, Université Paris 13)
**Frobenius twists in higher invariant theory**

17.00-18.30: drinks in the library of the Math building

Afterwards (19.30- ) there is a dinner in the Academiegebouw of the University of Utrecht. If you want to join (approx. 50 euro), please send an e-mail (also indicate if you have diet restrictions or if you want a vegetarian dinner) to both Jan Stienstra and Johan van de Leur (J.Stienstra@uu.nl and J.W.vandeLeur@uu.nl) before Thursday January 5.

**Abstracts:**

**Jean Fasel, Unimodular rows**

Let R be a commutative noetherian ring. A projective R-module P is said to be stably free if P⊕R^{n}≅R^{m}. By induction, the study of such modules reduces to the case P⊕R≅R^{s}. Such modules correspond to what is called unimodular rows of rank n. We will survey W. van der Kallen's work on such rows and then present some recent developments in the subject.

**
Henning Haahr Andersen, Tilting modules for reductive algebraic groups**

Let G be a reductive algebraic group over a field k, e.g. G
= GL_{n}(k). In this talk we shall describe the indecomposable tilting
modules for G and discuss some of their properties. We will also point to
some open problems in representation theory.

**
Antoine Touzé,
Frobenius twists in higher invariant theory**

Let V be a representation of the algebraic group GL_{n}(k). If k is a field of
positive characteristic, one can use the Frobenius isomorphism of x→x^{p} to form a twisted representation V^{(1)} of GL_{n}(k). Such representations
naturally appear in many problems from representation theory.
In this talk we will explain two results where such representations play
a crucial role. First they appear in the proof of van der Kallen's conjecture
(now a theorem Touzé, van der Kallen) that reductive algebraic groups have
finitely generated cohomology algebras. Second, extensions between such
twisted representations also control the cohomology of finite Lie groups (this
is a theorem by Cline, Parshall, Scott and van der Kallen). Then we will
give some very recent results on the cohomological behaviour of these twisted
representations.

This page will be updated if necessary.

January 12th, 2012 - **Workshop: Higher geometric structures along the Lower Rhine, MPIM Bonn, Jan 12-13, 2012
**

We would like to announce the first in a series of short workshops on higher geometric structures, jointly organized by the Geometry/Topology groups in Bonn, Nijmegen, and Utrecht, all situated along the Lower Rhine.

The first meeting will be held at the Max Planck Institute for Mathematics, on January 12-13, 2012.

The speakers are:

Dennis Borisov (MPIM Bonn)

Henrique Bursztyn (IMPA, Rio de Janeiro)

David Carchedi (MPIM Bonn)

Mikhail Kapranov (Yale)

Klaas Landsman (Nijmegen)

Stefan Schwede (Bonn)

Chenchang Zhu (Goettingen)

For registration and more information please go to the website of the workshop: http://www.mpim-bonn.mpg.de/node/3639

December 9th, 2011 - **GQT colloquium Amsterdam**

Speakers:

**13:00‒14:00 Klaas Landsman**:*The mathematics of mass: from the Higgs boson to Schrödinger's cat***14:30‒15:30 Jesper Grodal**:*Finite loop spaces***15:45‒16:45 Guido Carlet**:*WDVV equations and 2+1 integrable systems*

Location: VU University Amsterdam, main building, 8th floor, room HG-08A04 (how do I get there?)

Contact: Tilman Bauer

### Abstracts

####
**Klaas Landsman** (Radboud Universiteit Nijmegen): *The mathematics of mass: from the Higgs boson to Schrödinger's cat*

Since the Higgs boson has not been found (yet), the speaker is among many who take a critical look at the Higgs mechanism that underlies the generation of mass in the Standard Model of elementary particle physics. This leads to fascinating mathematical questions involving C*-algebras, ground states, symmetry (breaking), phase transitions, and, perhaps unexpectedly, the insight that the Higgs mechanism is predicated on a solution of the infamous measurement problem in quantum mechanics (which, in a world premiere, we will present).

####
**Jesper Grodal** (University of Copenhagen): *Finite loop spaces*

Hilbert's 5th problem, in its most basic form, asks if every compact topological group, which admits the structure of a smooth manifold, is a Lie group. In this form, it was answered affirmatively by von Neumann in 1929. If one takes a homotopical interpretation of the word "admits", the question is more subtle, and one is led to the notion of a finite loop space. These turn out not quite to be Lie groups, but nevertheless posses a rich enough structure to admit a classification. My talk will outline this story, which starts with a 1941 paper of Hopf: Über die Topologie der Gruppen-Mannigfaltigkeiten und ihre Verallgemeinerungen" and ends close to the present.

####
**Guido Carlet** (University of Copenhagen): *WDVV equations and 2+1 integrable systems*

Frobenius manifolds, originating as a geometrical formulation of WDVV equations of two-dimensional topological field theory, provide an important tool to study certain dispersionless integrable systems in 1+1 dimensions. Recently there has been some progress in the program of extending the Frobenius manifold techniques to the case of integrable systems with two spatial variables, the so-called 2+1 integrable hierarchies. In this case the associated Frobenius manifold is infinite-dimensional. We will recall some basic definitions and constructions in the theory of Frobenius manifolds and, considering the example of the 2D Toda hierarchy, we will show that they extend to the infinite-dimensional case, provided that we require some analytical properties of the Lax symbols.

November 14th, 2011 - **Lecture Jun Tomiyama: A proposal for non-commutative spectral synthesis
**

Time: 13.00-14.00 hr, room 412 of the Snellius building (Niels Bohrweg 1, Leiden)

October 14th, 2011 - **GQT Colloquium Utrecht**

The colloquium starts in the afternoon at 13.15 and will be held in Buys Ballot Laboratorium room 001.

**13.15-14.15: Simone Gutt** Symplectic Dirac operators and Mp^c structures

**14.30-15.30: Ieke Moerdijk** Infinity-Categories and Infinity-Operads

**15.30-16.00: coffee and tea **

**16.00-17.00: Carel Faber ** Modular forms and the cohomology of moduli spaces

**17.05-18.00: drinks**

**Abstracts**

**Simone Gutt:**
My talk will be based on some ongoing work with Michel Cahen and John Rawnsley.
Symplectic spinors have been introduced by Kostant on symplectic manifolds admitting
a metaplectic structure, (the metaplectic group being a double cover of the symplectic group,
the analogue of the Spin group in Riemmannian geometry).
In that context, K. and L. Habermann have introduced two natural Dirac operators,
choosing a compatible almost complex structure and a linear connexion preserving
the symplectic 2-form. The commutator of those operators is elliptic.
We extend the construction of symplectic Dirac operators to any symplectic manifold
through the use of Mp^c structures. The group Mp^c is the analogue of the
Riemmannian Spin^c and is a circle extension of the symplectic group.
Mp^c-structures exist on any symplectic manifold and equivalence
classes are parametrized by elements in H^2(M,Z).
For any Mp^c structure, choosing a compatible almost complex structures and a linear
connection, there are two natural Dirac operators,
acting on the sections of a spinor bundle, whose commutator
is elliptic. Using the Fock description of the spinor space allows the
definition of a notion of degree and the construction of a dense family of
finite dimensional subbundles stabilized by this operator.

**Carel Faber:**
This will be an overview over the cohomology classes
on moduli spaces of curves or abelian varieties (of low
genus respectively dimension) corresponding to modular
forms. Elliptic cusp forms give classes for curves of
genus 1, and their generalizations, Siegel cusp forms,
give classes for abelian varieties. One obtains a formula
for moduli of pointed curves of genus 2 in these terms.
For curves of higher genus, Teichmüller modular forms
enter the picture. The related cohomology classes are
still quite mysterious. (Joint work with Jonas Bergström
and Gerard van der Geer.)

June 17th, 2011 - **GQT colloquium Nijmegen**

Location: RU Nijmegen, Linneausgebouw, LIN 5

Schedule:

10:45-11:15 - Coffee and Tea

11:15-12:15 - Yong-Geun Oh

12:15-13:45 - Lunch

13:45-14:45 - Alexander Braverman

14:45-15:00 - Announcements of the GQT board

15:00-15:30 - Coffee and tea

15:30-16:30 - Erik van den Ban

16:30-18:00 - Reception (in the Huygens building)

Titles and abstracts:

- Yong-Geun Oh (University of Wisconsin-Madison): Counting embedded curves in Calabi-Yau threefolds and Gopakumar-Vafa invariants

The Gopakumar-Vafa BPS invariant is an integer invariant of the
cohomology of D-brane moduli spaces
on Calabi-Yau threefolds in string theory. By a conjectured relationship to
Gromov-Witten theory, it is
expected that the invariant coincides with the "number" of embedded
(pseudo-)holomorphic curves.
In this talk, we will explain how the latter integer invariants can be
defined for a generic
choice of compatible almost complex structures. If time permits, we will
comment on the corresponding
analog to the open string case and some implications on the wall-crossing
phenomenon and open questions towards complete solution to the
Gopakumar-Vafa
conjecture.

- Alexander Braverman (Brown University): Instanton counting and geometric representation theory

This talk will be a survey of known results about (equivariant) cohomology
and K-theory of various moduli spaces closely related
to the moduli space of principal G-bundles (here G is a simply connected
semi-simple algebraic group over complex number) on the
projective plane trivialized at infinity (this is also the same as the
moduli space on "instantons on R^4 framed at infinity").
The purpose of the talk will be two-fold:
1) Explain more precisely what kind of moduli spaces we should be talking
about and
explain why physicists what to integrate various cohomology (or K-theory)
classes over these moduli spaces and what kind of answers
they expect to get (and why).
2) Explain how one can understand the cohomology (or K-theory) of the above
moduli spaces by representation-theoretic means
and how this helps to prove predictions from 1 (in some cases).

- Erik van den Ban (Utrecht): Cusp forms on reductive symmetric spaces.
(joint work with Job Kuit)

For a real reductive Lie group G, there exists a
notion of cusp form, introduced by Harish-Chandra, who used this
terminology to emphasize the analogy with the general theory of automorphic forms.
The cusp forms coincide precisely with the discrete part
of the spectral decomposition of the space of square integrable functions on G.
This is in contrast with the theory of automorphic forms, where
the discrete part of the spectral decomposition is built from
cusp forms and residues of Eisenstein series, which in turn
are built from cusp forms of lower rank subgroups.
The class of reductive symmetric spaces contains that of the
real reductive groups. It would be interesting to have
a notion of cusp forms in this setting too. However, the definition
of cusp forms is somewhat problematic due to the divergence of
certain integrals. A number of years ago, M. Flensted-Jensen
suggested an idea for such a definition, but the convergence
of cuspidal integrals remained an unsolved issue in general.
In this talk, based on ongoing joint work with Job Kuit, I will
discuss this convergence problem, and present the solution
for symmetric spaces of split rank 1. It turns out
that in general the discrete spectrum splits into a cuspidal
and a residual part.

June 6th, 2011 - **EWM summer school**

The European Women in Mathematics organise a summer school for PhD students.

May 17th, 2011 - **Special day on Lie groups**

This workshop is organized at the occasion of the thesis defense of Job Kuit,
the day before.

Lectures:

11:00 - 11:50, T. Kobayashi (Univ. of Tokyo):
Restrictions of Verma modules to symmetric pairs and some applications to differential geometry

13:00 - 13:50, S. Helgason (MIT): TBA

14:10 - 15:00, H. Schlichtkrull (Univ of Copenhagen):
Decay on homogeneous spaces of reductive type

Detailed program

May 16th, 2011 - **Thesis defense of Job Kuit**

On Monday May 16, 14:30, Job Kuit will defend his thesis: "Radon transformation for reductive symmetric spaces: support theorems".

April 8th, 2011 - **GQT Colloquium **

Place: Minnaert building room 211, de Uithof, Utrecht.

10.45 - 11.15 Coffee & tea

11.15 - 12.15 ** Gerard van der Geer** Modular forms for genus three

12.15 - 14.00 Lunch

14.00 - 15.00 ** Ulrike Tillmann ** Cobordism theory: old and new

15.00 - 15.30 Coffee & tea

15.30 - 16.30 ** Arno Kuijlaars ** Multiple orthogonal polynomials and random matrix eigenvalues

16.30 - Drinks in Library Math. building

**Abstract **

** Ulrike Tillmann **

With the work of Thom in the early 1950s cobordism theory became an important tool for the classification of smooth manifolds. Cobordisms played a very different role in the axiomatic approach to topological quantum field theory by Atiyah and Segal in the late 1980s.
In this lecture I will bring these two themes together and explain how recent results shed new light on both of these.

**Arno Kuijlaars**

The Gaussian Unitary Ensemble is the simplest unitary invariant
random matrix ensemble. Its eigenvalues can be analyzed
in full detail with the use of Hermite polynomials.
General unitary ensembles are associated with
orthogonal polynomials with exponential weights. In the fundamental
work of Deift et al. (1999) the steepest descent analysis of the
Riemann-Hilbert problem for these polynomials was developed
in order to establish universality for eigenvalue spacings.
Multiple orthogonal polynomials play a similar role in
certain other random matrix ensembles such as the random matrix
model with external source, and the two-matrix model. I will discuss
the Riemann-Hilbert problem and a vector equilibrium problem that
describes the global distribution of eigenvalues and is
crucial for the asymptotic analysis.

February 18th, 2011 - **Inaugural Lecture Nicolai Reshetikhin
**

Title: The harmony of Mathematics and Physics

Date/Time: Friday, February 18, 2011, 16:00

Location: Aula of the University of Amsterdam, Singel 411

February 18th, 2011 - **GQT Colloquium**

The GQT Colloquium on Friday, February 18, 2011, will be combined with the inaugural lecture of Nicolai Reshetikhin.

**Venue:** Zaal AB.44, gebouw A, Roetersstraat 15, 1018 WB Amsterdam.

**Schedule:**

10:50-11:15 Coffee and tea

11:15-12:15 Talk Marc Levine

12:15-13:45 Lunch break

13:45-14:45 Talk Michel van den Bergh

After the last lecture everybody is invited to attend the inaugural lecture of Nicolai Reshetikhin,
See
"The harmony of Mathematics and Physics".

**Talks**

**Mark Levine**: Some applications of algebraic cobordism.

Abstract: Algebraic cobordism is a version in algebraic geometry of the topological theory of complex cobordism. Originally, it was constructed to help understand rather subtle divisibility properties of characteristic classes, which in turn leads to some interesting results on homogeneous varieties over non-algebraically closed field. Later on,
Pandharipande saw how to apply this theory to solve problems in Donaldson-Thomas theory. I will describe the theory of algebraic cobordism and say a bit about its original series of applications to homogeneous varieties, then turn to the work on Donaldson-Thomas theory and conclude with some more recent work of Pandharipande, Lee and Tzeng using algebraic cobordism to study problems in Gromow-Witten theory.

**Michel van den Bergh**: Formality and deformations.

Abstract: Kontsevich's celebrated formality theorem shows that every Poisson bracket
on a C^infty manifold can be quantized into a start product. For a smooth
algebraic variety this is not quite true. We will discuss the algebraic version
of the formality theorem and its relation to deformation theory.
We will also discuss how algebraic formality may be used to prove a conjecture by Caldararu which gives an intriguing connection between algebraic geometry and
Lie theory.

December 20th, 2010 - **Seminar on geometry and topology (UU)
**

Date: Monday 20 December

Place: room 611, Mathematics Building, Utrecht

Schedule:

11:00-12:00: Hessel Posthuma (Amsterdam)

Integrable hierarchies and Frobenius manifolds

15:00-16:00: Julie Bergner (UC Riverside)

Generalized classifying space constructions

16:30-17:30: Christian Blohmann (Regensburg/Bonn)

Homotopy equivalence of correspondences and anafunctors of higher groupoids

Abstracts can be found on the website

December 10th, 2010 - **GQT colloquium**

Speakers:

Frederic Bourgeois (Bruxelles): Holomorphic curves in contact geometry

Holomorphic curves were introduced in symplectic geometry by Gromov.
These rapidly proved to be extremely valuable tools to study symplectic
rigidity and to construct symplectic invariants. The goal of this talk
is to explain how these techniques can also be applied to contact
geometry, with a focus on contact homology, a holomorphic curves
invariant for contact structures. This will be illustrated with
several examples and some selected results.

Walter van Suijlekom (Nijmegen): Gauge theories and noncommutative manifolds

In this talk, we will discuss some aspects of the intrinsic gauge
theoretical nature of noncommutative manifolds. Following Connes, we
descibe a noncommutative (Riemannian, spin) manifold by its fundamental
class in K-homology. Among other functional analytical data, such a
K-cycle consists of a (noncommutative) C*-algebra. As a consequence of
noncommutativity, there might exist non-trivial inner automorphisms;
these will be referred to as gauge transformations.
The key example that motivates this terminology from physics is when one
replaces the algebra of functions on a manifold by matrix-valued
functions. The resulting Morita equivalence describes ordinary
Yang-Mills theory as formulated in terms of connections on principal
bundles.
As another class of examples, we will discuss deformations of a manifold
along a torus action, first introduced by Rieffel. The noncommutative
algebra turns out to contain a commutative subalgebra, corresponding to
functions that are constant along the orbits of the torus (and hence
remain undeformed). We will present a novel interpretation of the
noncommutative K-cycle as describing a gauge theory on the (commutative)
orbit space. The gauge theory naturally involves connections on Hilbert
bundles on this background manifold. If time permits, we formulate a
decomposition in Kasparov's KK-theory that captures this and the above
example.

Ilia Itenberg (Strasbourg): Tropical geometry and enumeration of real rational curves

The purpose of the talk is to make an introduction
to tropical geometry
with an emphasis on applications of tropical geometry
in complex and real algebraic geometries.
Tropical geometry has deep relations
with many branches of mathematics.
In good cases, a tropical variety is approximated
by a one-dimensional family of complex varieties.
This gives rise to important links
between the complex algebraic world and the
tropical one. One of the links
is given by Mikhalkin's correspondence theorem.
This theorem, together with Welschinger's discovery
of a real analog of genus zero Gromov-Witten invariants,
produces new results on enumeration of real rational curves.
We will also discuss tropical homology groups
which carry an important information
about a degenerating one-dimensional family
of complex varieties.

Program:

10:50-11:15 Coffee and tea (outside LIN 6)

11:15-12:15 Talk of F. Bourgeois (LIN 6)

12:15-13:45 Lunch break

13:45-14:45 Talk of W. van Suijlekom (LIN 3)

14:45-15:00 Messages from the GQT board, awarding of the GQT master thesis prize, discussion of GQT programme MasterMath

15:00-15:20 Coffee and tea

15:20-16:20 Talk of I. Itenberg (LIN 3)

16:30-??:?? Borrel (Huygensbuilding)

All talks will take place in the Linnaeus building (Heyendalseweg 137),
but in different rooms for morning and afternoon sessions.

October 8th, 2010 - **GQT colloquium**

The colloquium will take place at Science Park 904, 1098 XH Amsterdam, **room A1.04**.
The speakers are Tilman Bauer (VU Amsterdam), Viatcheslav Kharlamov (IRMA, Strasbourg), and Robert Penner (Aarhus Univ. and Caltech).

Schedule:

10:30 - 11:00: Coffee and tea.

11:00 - 12:00: Talk of Robert Penner.

12:00 - 14:00: Lunch.

14:00 - 15:00: Talk of Viatcheslav Kharlamov.

15:00 - 15:30: Coffee and tea.

15:30 - 16:30: Talk of Tilman Bauer.

16:30 - ??:??: Reception

Directions: room A1.04,
Science Park 904.

Titles and abstracts of the talks.

Tilman Bauer: **Unstable operations in Morava K-theory.**

Abstract:

The Morava K-theories are a familiy of homology theories which are singled out among other homology theories by the fact that they behave analogously to the prime fields $\mathbb{F}_p$ among all abelian groups. I will show how these can be used effectively to compute the homotopy groups of a space (or, more precisely, of a localization of a space) using an Adams-type spectral sequence.

Viatcheslav Kharlamov: **First steps in enumeration of real rational curves on surfaces.
Welschinger invariants, their definitions and properties.**

Abstract:

Welschinger invariants is a real analogue of genus zero Gromov-Witten invariants.
Their general theory is still under construction but they gave already
a number of non-trivial applications, especially in real enumerative geometry where
they remain the main source of lower bounds on the number of real solutions
(one may mention as one of the first applications of the Welschinger invariants
a proof of the existence of real solutions in the problem of interpolating real points by
real rational plane curves of given degree). In this talk, based on joint works with I. Itenberg and E. Shustin,
I will remind how Welschinger invariants look like in the case of surfaces,
point certain modifications, and then concentrate on some basic properties (like positivity,
monotonicity and asymptotic growth) obtained in the case of Del Pezzo surfaces (with $K2\ge 3$ for the moment) by means of real analogues of Caporaso-Harris type recursive formulas.

Robert Penner: **Protein and RNA Moduli Spaces.**

Abstract:

Several joint projects with J. E. Andersen and others have applied
techniques and results from moduli spaces to various problems in
proteomics and genomics. Protein has its characteristic geometric
structure, which is naturally modeled using spaces of SO(3)
graph connections, leading to a nice notion of protein moduli space.
In genomics, the geometry is less well understood, in part because of
the dearth of data, but the combinatorics nevertheless remains useful: Earlier joint work with M. S. Waterman had analyzed moduli spaces of all possible unknotted RNA secondary structures using planar fatgraphs, and current joint work with JEA, MSW, and C. M. Reidys goes beyond this towards solving the problem of enumerating all possible knotted RNA secondary structures of a specified topology with its concomitant applications to the RNA folding problem.

October 5th, 2010 - **symposium on quantum probability and quantum information **

Place: Minnaertbuilding room 023, de Uithof, Utrecht

Program:

11:00-12:00: Hans Maassen

Introduction to quantum probability and quantum information

(lunch break)

13:00-14:00: Nilanjana Datta

Relative entropies and entanglement monotones

14:15-15:15: Mark Fannes

Entropic bounds for correlated states

(tea break)

15:45-16:45: Madalin Guta

Fisher information and asymptotic normality for quantum Markov chains

(drinks)

If you want to attend, please send an e-mail to: J.W.vandeLeur"AT"uu.nl

October 4th, 2010 - **Promotie Bas Janssens**

Titel Proefschrift: Transformation & Uncertainty (Some Thoughts on Quantum Probability Theory, Quantum Statistics, and Natural Bundles)

Academiegebouw Utrecht, Domplein 29, Utrecht

Aanvang 14.30 uur

September 10th, 2010 - **Workshop Quantum Topology**

September 10-11, 2010

June 28th, 2010 - **GQT conference: 28/6 - 2/7, 2010. Registration open.**

Conference at the occasion of the fourth year of existence of the
GQT cluster.

June 10th, 2010 - **P. Aluffi (FSU): 10-15 June: Three lectures on characteristic classes and Feynman integrals**

P. Aluffi (FSU) will give a "masterclass in the masterclass": 8-17 June: Characteristic classes and Feynman integrals, Time/Location: 15-17 on Thu 10/6 in Minnaertgebouw 202, Mon 14/6, Tue 15/6 in WIS611

June 9th, 2010 - **M. Marcolli (Caltech), 8-17 June: lectures "How noncommutative geometry looks at arithmetic"**

M. Marcolli (Caltech) will give a "masterclass in the masterclass" at Utrecht, 8-17 June: How noncommutative geometry looks at arithmetic
Time: 11-13 on Wed 9/6, Thu 10/6, Mon 14/6, Tue 15/6 and Wed 16/6; Location: WIS611, *Everybody welcome! Priority to MRI-masterclass students*

June 9th, 2010 - **G. Felder lectures on 9/6, 22/6, 24/6.**

Giovanni Felder from ETH in Zurich will be the guest of the Mathematics Department of the Radboud University Nijmegen from June 8 until July 3 of this year, as visiting GQT-professor.

He will give a general colloquium lecture on

This lecture is intended for a general mathematical audience.

There will be two days of lectures the week before the GQT-conference. On both of these days we intend to have dinner in town with the speakers and the audience of the lectures. If you are interested, please join us.

June 4th, 2010 - **GQT colloquium Utrecht**

**Place: Minnaert building room 208, Utrecht**

10:50-11:15 Coffee and tea

11:15-12:15 Talk of Yan Soibelman

12:15-14:00 Lunch break

14:00-15:00 Talk of Gert Heckman

15:00-15:25 Coffee and tea

15:25-15:30 Message from the board of GQT

15:30-16:30 Talk of Alexei Davydov

16:45-??:?? Drinks in Library Math building

**Abstracts.**

**
Yan Soibelman:** Motivic Donaldson-Thomas invariants and cluster transformations.

In a joint work with Maxim Kontsevich we introduced motivic
Donaldson-Thomas invariants of 3-dimensional Calabi-Yau categories. Such a
category can be associated e.g. with a quiver with potential. Mutation of
the quiver with potential corresponds to a change of t-structure of the
Calabi-Yau category. Comparing motivic DT-invariants calculated in those
two t-structures we arrive to the quantum cluster transformation of the
quantum torus naturally associated with the Grothendieck group of the
category.
I am going to explain this result with the necessary preliminaries.

**
Gert Heckman:** Hyperbolic Structures and Root Systems

We discuss the construction of a one parameter family
of complex hyperbolic structures on the complement of a toric mirror
arrangement associated with a simply laced root system. Subsequently
we find conditions for which parameter values this leads to ball quotients.

**Alexei Davydov:** Witt group of modular categories"
(joint with A. Kitaev, M. Mueger, D. Nikshych, V. Ostrik)

We describe an abelian group structure on the set of classes of
modular categories modulo some equivalence relation.
The resulting Witt group of modular categories resembles (and
contains) the Witt group of finite abelian
groups with quadratic forms.
The conjecture of Moore and Seiberg, that all RCFTs come from
reductive groups via WZW, coset and orbifold constructions, can be
interpreted as a statement about generators of this Witt group.

May 31st, 2010 - **Master Class "Geometry of Gauge Theories and Geometric Quantization"**

This master class will be held at the University of Amsterdam (at the science park) from **May 31 -- June 11, 2010** and is also suitable for master students (4 credit points).

Lectures by **N. Reshetikin** and **J.E. Andersen**.

Further information may be obtained from
the website,
where one can register for the master class (registration deadline is March 29th).

Information may also be requested at masterclassmph@gmail.com

May 4th, 2010 - **Talk by Pablo Roman (KU Leuven) in Mathematical Physics Seminar.**

Title: Matrix valued orthogonal polynomials, spherical functions and the hypergeometric operator.
Time and place: Tuesday May 4, 2010 (9:30-10:30) in room HG03.084

April 27th, 2010 - **Lecture O. Garcia-Prada**

O. Garcia-Prada (CSIC Madrid/MPI Bonn) will give a talk at the UvA:

Title: Involutions of the moduli space of Higgs bundles and real forms

Abstract. We consider involutions of the moduli space of G-Higgs
bundles over a compact Riemann surface, where $G$ is a complex
reductive Lie group, and study the relation of the fixed points
subvarieties with representations of the fundamental group of
the surface into real forms of G.

Room: A1.04, Science Park Amsterdam

Time: 16:00-17:00

April 26th, 2010 - **Masterclass W. van Suijlekom (RU Nijmegen): 26-29 april: Noncommutative geometry and physics **

W. van Suijlekom (RU Nijmegen) will give a "masterclass in the masterclass" at Utrecht, 26-29 april: Noncommutative geometry and physics
Time: 9-11 on Mon 26/4, Wed 28/4 and Thu 29/4; Location: WIS611, *Everybody welcome! Priority to MRI-masterclass students*

April 16th, 2010 - **GQT colloquium Leiden**

The GQT colloquium will be the last day of the MRI/GQT conference **The Interface of Integrability and Quantization ** which will be held at the Lorentz Center from 12 Apr 2010 through 16 Apr 2010.

March 15th, 2010 - **Masterclass C. Consani (JHU): 15-17 March: Around the field with one element**

C. Consani (Johns Hopkins) will give a "masterclass in the masterclass" lecture 15-17 March: Around the field with one element, Time: Mon 15/3, 9-12 and Wed 17/3, 9-11; Location: BBL005, *Everybody welcome! Priority to MRI-masterclass students*

March 1st, 2010 - **Masterclass G. Robertson (Newcastle): 1-5 March: Noncommutative geometry of euclidean buildings and their boundaries
**

Guyan Robertson (Newcastle) will give a "masterclass in the masterclass" lecture at Utrecht ,1-5 March: Noncommutative geometry of euclidean buildings and their boundaries, Time: 9-11, Locations: Mon 1/3 in BBL005, Wed 3/3, Thu 4/3, Fri 5/3: WIS611 *Everybody welcome! Priority to MRI-masterclass students*

February 12th, 2010 - **GQT colloquium Amsterdam**

The colloquium will take place at the new building of the FNWI at Science Park 904, 1098XH Amsterdam, **Room A1.10.**

Program:

10:50-11:15 Coffee and tea

11:15-12:15 Talk of S. Bloch

12:15-14:00 Lunch break

14:00-15:00 Talk of M.-T. Benameur

15:00-15:25 Coffee and tea

15:25-15:30 Message from the board of GQT

15:30-16:30 Talk of M. Crainic

16:30-??:?? Borrel

The list of talks:

**Spencer Bloch**, Chicago

Title: ** Introduction to iterated integrals and multiple zeta-numbers.**

Abstract: (Relativistic) Quantum Field Theory is a rich source of fascinating problems in algebraic geometry. In this lecture I will outline some general questions involving physics and algebraic geometry (motives).

I. Iterated integrals; multiple zeta-numbers.

II. Graphs; Feynman rules; Feynman amplitudes; Feynman parameters.

III. External momenta and masses.

IV. Renormalization; limiting mixed Hodge structures.

V. Monodromy; Cutkowsky Rules.

**Moulay-Tahar Benameur**, Metz

Title: **The foliated Cheeger-Gromov invariant.**

Abstract: We shall review the classical rho invariant and introduce the foliated rho invariant associated with a holonomy invariant measure on a smooth closed odd foliation. Then we shall explain a foliated homotopy invariance theorem for the signature operator.

**Marius Crainic**, Utrecht

Title: ** Local forms in Poisson geometry.**

Abstract: I will report on recent joint work with
Ionut Marcut (PhD student, UU) on a Poisson geometric
version of the slice theorem (in equivariant geometry)
and of the local Reeb stability (in foliation theory).
This theorem is a generalization of Conn's linearization
theorem- a generalization which is possible due to recent
geometric proof (joint with R.L. Fernandes) of Conn's theorem.
I will spend most on the time on recalling the classical
results, explaining the result and looking at examples.
If time allows, some ideas of the proof will be given.

January 25th, 2010 - **Stieltjes Onderwijsweek 2010**

From 25 till 28 January 2010 a "Stieltjesonderwijsweek" will take place at the VU, mainly aimed at PhD students and postdocs. It will provide a good background for the talks of Spencer Bloch as Stieltjes professor during February and March 2010, but the chosen subjects are of independent interest in algebraic geometry and related fields.
It gives an introduction to the following topics
* Cohomology theories
* Mixed Hodge structures and their variations.
* Local systems and monodromy.

Organizers: Bas Edixhoven, Rob de Jeu, Ben Moonen, Tejaswi Navilarekallu, Jan Stienstra, Lenny Taelman.

For more details see:

http://www.few.vu.nl/~jeu/Stieltjesonderwijsweek-2010.html

December 22nd, 2009 - **Special day on Lie groups**

At the occasion of the thesis defense of Vincent van der Noort

Program:

Location: Buys Ballot Laboratory, 426

Organizer: Erik van den Ban

December 21st, 2009 - **Thesis defense Vincent van der Noort**

Title: `Analytic parameter dependence of Harish-Chandra modules for real
reductive Lie groups -- A family affair'

Promotor: E.P. van den Ban

Date, time: Monday, December 21, 14:30

Location: Academiegebouw, Domplein 29

December 11th, 2009 - **GQT colloquium Utrecht**

The first lecture of the colloquium will take place in Minnnaertbuilding room 208; lecture 2 and 3 in Minnnaertbuilding room 202.

Program:

10:50-11:15 Coffee and tea

11:15-12:15 Talk of Alexander Polishchuk

12:15-14:00 Lunch break

14:00-14:05 Student prize Ceremony: Best GQT 2008-2009 M.Sc.-thesis

14:05-15:05 Talk of Ben Moonen

15:05-15:30 Coffee and tea

15:30-15:35 Message from the board of GQT

15:35-16:35 Talk of Boris Dubrovin

16:35-??:?? Drinks

The list of talks:

Alexander Polishchuk

Title: A-infinity structures on elliptic curves.

Abstract: I will show how calculating A-infinity structures on the derived category of coherent sheaves of an elliptic curve leads to new expressions for
some classical functions, such as Eisenstein series and Hecke's indefinite theta series.

Ben Moonen

Title: Chern classes of automorphic bundles

Abstract:In my talk I shall discuss tautological classes on compactified Shimura varieties. By definition, the algebra of such classes is generated by the Chern classes of certain natural vector bundles. The picture we have is that for the Shimura variety associated to a pair (G,X) the tautological ring should be isomorphic to the cohomology ring of the compact dual of X, which is a completely explicit ring. We give a simple geometric explanation for this. In cohomology this works. However, on more refined levels (Deligne cohomology, Chow rings) we know this only in special cases and there is a fundamental obstacle that remains. I shall describe where the difficulty lies and will discuss what is known about it. If time permits I will explain how in characteristic p these difficulties can be overcome.

No prior knowledge of the formalism of Shimura varieties is assumed!

Boris Dubrovin

Title: Hamiltonian PDEs and their deformations

Abstract: We will explain basic ideas of the deformation theory of Hamiltonian partial differential equations (PDEs), including an introduction to integrable PDEs. In the second part of the talk some properties of solutions to these PDEs will be discussed.

December 1st, 2009 - **Talk by Simon Brain (SISSA, Trieste) in Seminar on Quantization, noncommutative geometry and symmetry **

Simon Brain will speak on "The Noncommutative Geometry of Instantons on S^{4}_{&theta}".
Time: 15:45
Location: HG03.084

October 29th, 2009 - **2-day workshop "Geometric Aspects of Quantum Theory
and Integrable Systems"**

The workshop will take place at the University of Amsterdam, Roeterseiland.

**Thursday; October 29**

All lectures will be held in room 3.85 of building J/K at the Valckenierstraat

10:15-11:15 N. Reshitikhin, On the large volume limit of random skew plane partitions

11:15-11:30 Break

11:30-12:30 A. Zabrodin, Logarithmic gases and Laplacian growth

12:30-14:00 Lunch break

14:00-15:00 M. Mazocco, Isomonodromic deformations arising in Teichmuller theory

15:00-15:15 Break

15:15-16:15 L. Chekhov, From Teichmuller spaces to Yangian algebras: quantization and reductions

16:15-16:30 Break

16:30-17:30 G. Carlet, The innite dimensional Frobenius manifold associated to 2D Toda hierarchy

**Friday; October 30**

All lectures will be held in room 3.06 of building A at the Roeterstraat

10:15-11:15 I. Krasil'shchik, Poisson structures in the geometry of PDEs

11:15-11:30 Break

11:30-12:30 S. Loktev, Topological Field Theories for non-orientable Surfaces

12:30-14:00 Lunch break

14:00-15:00 J. S. Caux, Correlations and quenches in integrable systems

15:00-15:15 Break

15:15-16:15 S. Shadrin, A cohomological field theory associated to a TCFT

16:15-??:?? Drinks

Abstracts of the talks are available at the web-page of the workshop at KdVI.

The workshop is organised by **Gerard Helminck** in in collaboration with the Institute for Theoretical Physics.

October 9th, 2009 - **GQT colloquium Amsterdam**

The colloquium will take place at the old building of the Korteweg-de Vries Institute (Euclides) at Plantage Muidergracht 24, 1018TV Amsterdam, **Room P.018.**

Program:

10:50-11:15 Coffee and tea

11:15-12:15 Talk of V. Fock

12:15-14:00 Lunch break

14:00-15:00 Talk of A. Alekseev

15:00-15:25 Coffee and tea

15:25-15:30 Message from the board of GQT

15:30-16:30 Talk of J. van de Leur

16:30-??:?? Borrel

The list of talks:

**Anton Alekseev**, Geneva

Title: **Associators and their applications**

Abstract: Drinfeld associators were originally introduced as a tool in the theory of
quantum groups. It was later discovered that they play an important role
in many fields of mathematics, such as Lie theory, low-dimensional
topology, deformation quantization and number theory.

In the talk, we'll introduce the Drinfeld's pentagon equation and explain
its links to the Kashiwara-Vergne problem in Lie theory and to multiple
zeta values in number theory.

**Vladimir Fock**, Strasbourg

Title: **Cluster geometry and quantum theory of higher Teichmueller spaces.**

Abstract: Ordinary Teichmueller space of complex structures on Riemann surfaces can be viewed as a connected component in the space of homomorphisms of the fundamental group of the surface to the group $SL(2,R)$. Higher Teichmueller space, defined by Hitchin, is a generalisation of this notion in where the group $SL(2,R)$ is replaced by a simple group of higher rank. We shall give an explicit description of this space and discuss its structures: mapping class group action, Poisson structure and quantization.

**Johan van de Leur**, Utrecht

Title: **Givental symmetries of Frobenius manifolds and multi-component KP tau-functions**

Abstract: We establish a link between two different constructions of the action of the twisted loop group on the space of Frobenius structures. The first construction (due to Givental) describes the action of the twisted loop group on the partition functions of formal Gromov-Witten theories. The explicit formulas for the corresponding tangent action were computed by Y.-P. Lee. The second construction describes the action of the same group on the space of Frobenius structures via the multi-component KP hierarchies. Our main theorem states that the genus zero restriction of the Y.-P. Lee formulas coincides with the tangent KP action.
This talk is based on arXiv:0905.0795 wich is a joint publication with Evgeny Feigin and Sergey Shadrin.

July 17th, 2009 - **Day on Special Functions**

Speakers: Wolter Groenevelt (TUD), Raimundas Vidunas (Kobe University, Japan), Mizan Rahman (Carleton University, Canada), Tom Koornwinder (UvA)

June 15th, 2009 - **The analytic theory of automorphic forms**

A conference at the 65th birthday of Roelof Bruggeman

15-19 June 2009

Speakers include: Eiichi Bannai (Kyushu), Ehud Moshe Baruch (Technion), Kathrin Bringmann (Koln), Roelof Bruggeman (Utrecht), Gautam Chinta (CUNY), Nikolaos Diamantis (Nottingham), Masanobu Kaneko (Kyushu), Emmanuel Kowalski (ETHZ), Winnie Li (Penn State), Anton Mellit (MPIM), Roberto Miatello (Cordoba), Andre Reznikov (Bar Ilan), Morten Risager (Kopenhagen), Akshay Venkatesh (Stanford), Nolan Wallach (UCSD), Don Zagier (College de France/MPIM), Sander Zwegers (UC Dublin).

For more information and registration, go to the webpage. To secure a place at the conference, register before mid March.

June 9th, 2009 - **Talk by Xiang Tang in Utrecht in the Geometry and Topology seminar**

14.00, room tba

Title: Relative index of CR structures

Abstract: We discuss a new proof of the Atiyah-Weinstein conjecture on the index of Fourier integral operators and the relative index of CR structures. This talk is based on a recent joint work with Boutet de Monvel, Leichtnam, and Weinstein.

June 5th, 2009 - **GQT colloquium Nijmegen**

Locatie: Linnaeusgebouw, zaal LIN 3

Programme:

10:45 - 11:00: Koffie/thee

11:00 - 12:00: Giovanni Felder (Zürich):
Holomorphic differential operators and Riemann-Roch formulae.

12:00 - 13:30: lunch pauze

13:30 - 13:45: mededelingen van het GQT bestuur

13:45 - 14:45: Tillman Wurzbacher (Metz): On the (hypothetical) Dirac operator on loop space:
Topological, geometrical and analytical aspects

15:00 - 16:00: Victor Kac (MIT): Poisson vertex algebras in the theory of infinite-dimensional Hamiltonian equations.

16:00 - : Receptie (Huygensgebouw, bij de wiskunde afdeling).

Abstract Felder's talk:
The Riemann-Roch formula extends to a local integral formula for the alternating sum of traces of the action a holomorphic differential operator on sheaf cohomology. In the presence of a compact group action, localization formulae at fixed points are available. The construction is based on ideas of deformation quantization. This is joint work with Markus Engeli and with Xiang Tang based on earlier work with Boris Feigin and Boris Shoikhet.

June 4th, 2009 - **Talk by Xiang Tang at the KdV-institute (UvA)**

11.00, Room A1.06, Sciencepark 904 (the new location of the KdV institute!)

Title: Hochschild cohomology of orbifolds and Dunkl operators

Abstract: We will explain how Dunkl operators show up in the study of Hochschild cohomology of orbifolds. After that, we plan to discuss an approach to use Dunkl operators to construct some "new" deformation quantizations of orbifolds.

April 29th, 2009 - **Lecture by M. Lehn**

Title: Holomorphic symplectic varieties

Location: KdV Institute, UvA, room P.014
Time: 11:15 - 12:00.

April 17th, 2009 - **Seminar on Modular Forms**

14:00-14:50 Matthias Schuett (University of Copenhagen)

*K3 surfaces and modular forms*

15:00-15:50 Gerard van der Geer (University of Amsterdam)

*Siegel modular forms of low genera*

16:00 Coffee/Tea

16:30-17:20 Don Zagier (MPIM Bonn/ CdF Paris)

*On a U(3,1)-automorphic form of Ferapontov-Odesskii*

18:00 Dinner

April 3rd, 2009 - **G. Laumon: The weighted fundamental lemma**

Two lectures (joint work with P.-H. Chaudouard)

March 20th, 2009 - **DIAMANT-GQT colloquium **

10.45.00-17.00 h. in Minnaertgebouw 208, Universiteit Utrecht:

10.45-11.00 coffee and tea

11.00-12.00: Spencer Bloch, Algebraic geometry associated to graphs

12.00-13.15: Lunch

13.15-14.15: Alex Quintero Velez, McKay correspondence for Landau-Ginzburg models

14.30-15.30: Rob de Jeu, K4 of curves over number fields

15.30-16.00: Tea and coffee

16.00-17.00: Dmitri Orlov, Triangulated categories of singularities, D-branes in LG-models and mirror symmetry

17.05- : Drinks in the library of the Mathematical Institute

Abstracts:

Spencer Bloch, Algebraic geometry associated to graphs

The Feynman amplitude associated to a graph in physics is a period of the hypersurface defined by the Kirchoff polynomial, a classical invariant of the graph. I will explain work on the "motive" of the graph.

Alex Quintero Velez, McKay correspondence for Landau-Ginzburg models

Abstract: The McKay correspondence is a principle that relates the geometry of a resolution of singularities of a quotient variety M/G and the equivariant geometry of the group action. The classic case is McKay's identification of the cohomology of the resolution of a Kleinian singularity CC2/G with the representation theory of G. In this talk, we discuss an analogue of the McKay correspondence for Landau-Ginzburg models. This leads naturally to a generalized notion of the McKay correspondence as an isomorphism of "noncommutative spaces" (in Kontsevich's sense).

Rob de Jeu, K4 of curves over number fields

We give a conjectural description (due to Goncharov) of K4 modulo torsion of a curve over a number field, using certain complexes based on the function field of the curve. We also discuss to which extent this has been proved. Furthermore, we illustrate a method of finding non-zero examples for elliptic curves E defined over Q, and numerically verify the relation between their regulators and L(E,3) predicted by the Beilinson conjectures. The latter is joint work in progress with Sander Meinema.

Dmitri Orlov, Triangulated categories of singularities, D-branes in LG-models and mirror symmetry

I am going to talk about triangulated categories of singularities and categories of D-branes of type B in Landau-Ginzburg models and sigma-models. Different properties of these categories will be described. At the end of my talk I am also going to discuss mirror symmetry and a generalized strange Arnold duality.

March 2nd, 2009 - **Thesis defense Alex Quintero **

Thesis: Equivalence of D-Brane Categories

Author: Alexander Quintero Velez

Promotor: Hans Duistermaat, copromotor: Jan Stienstra

Date/Time: Monday 2/3-2009, 12:45

February 27th, 2009 - **Math-Physics seminar**

Lectures from 14:00 - 16:30, Buys Ballot 276, followed by drinks

**Speakers:**

**Abstracts:**

**Dancer:**We use dynamical systems methods to produce new examples of Ricci solitons, including some not of Kahler type.

**Zabzine:**Chiral de Rham complex is the way to associate the conformal field theory to a curved target space. I will briefly review the ideas behind the chiral de Rham complex. I will discuss the relation between chiral de Rham complex and the generalized geometry. I will conclude with the brief comments on the applications

(organizers: Bernard de Wit, Eduard Looijenga, Jan Stienstra, Stefan Vandoren)

February 6th, 2009 - **GQT colloquium at Amsterdam**

The speakers are Arthur Bartels (Univ. of Muenster), Ezra Getzler (Northwestern Univ.), and Jasper Stokman (Univ. of Amsterdam).

Schedule:

10:45 - 11:00: Coffee and tea

11:00 - 12:00, Room P 0.14: Ezra Getzler.

12:00 - 13:30: Lunch

13:30 - 14:30, Room G.S.04: Arthur Bartels.

14:30 - 14:45: Coffee and tea

14:45 - 15:45, Room G.S.04: Jasper Stokman.

16:00 - ??:??, Euclides canteen: Reception

Directions.

Building P (1st lecture and reception): Plantage Muidergracht 22-24,
1018 TV Amsterdam

Building G (2nd and 3rd lectures): Nieuwe Prinsengracht 130, 1018 VZ Amsterdam

Transport schedule can be obtained from 9292ov.nl

Titles and abstracts of the talks.

Ezra Getzler: **Gerbes and supergravity.**

Abstract:

Four-dimensional supergravity is a classical field theory involving
the addition of a matter field, called the Rarita-Schwinger field, to
Einstein's theory of gravitation. The local covariance exhibited by
Einstein's theory (in contemporary language, equivariance under the
action of the Lie algebra of vector fields) is generalized in
supergravity to the action of a Lie superalgebra; this symmetry is
called local supersymmetry.

By contrast with the situation in the theory of gravity, the
supersymmetry of supergravity is not exhibited at the level of the
field equations, but only on the space of solutions of these
equations; physicists say that supersymmetry only holds "on-shell".
There is an equivalent formulation of supergravity, involving the
addition of a pair of new fields, a Hermitian connection A on a
complex line bundle and a two-form B, such that the resulting theory
exhibits supersymmetry "off-shell", even before imposing the equations
of motion; this theory, introduced by Sohnius and West, is called "new
minimal supergravity".

In this talk, we interpret the two-form as the curving of a gerbe, and
the coupling between the fields A and B in terms of Beilinson's
product on Deligne cohomology. This permits the definition of new
minimal supergravity not just on domains of Minkowski space, but on
manifolds.

Applying this formalism to the double of a manifold with boundary, we
explain how to formulate new minimal supergravity in the presence of a
boundary. (Here, we are expanding on a discussion by Lambert and
Moore.) Here, Z/2-equivariant gerbes make their appearance.

One of the goals of this talk is to offer an introduction to gerbes
and their geometry - little background beyond familiarity with
differential forms and connections on line bundles will be assumed.

Arthur Bartels: **Hyperbolic groups and aspherical manifolds.**

Abstract:

An aspherical manifold is a closed manifold whose universal cover is contractible. Up to homotopy such a manifold is determined by its fundamental group. Borel conjectured that
such a manifold is in fact determined up to homeomorphism by
its fundamental group. It is also of interest to determine
which groups arise as fundamental groups of aspherical manifolds. I will discuss these questions for word-hyperbolic groups in the sense of Gromov.

Jasper Stokman: **Affine Hecke algebras and bispectral quantum KZ equations.**

Abstract:

I first review the role of the affine Hecke algebra H
in the construction of quantum invariants of braids and ribbon tangles
in a thickened cylinder, as well as its application in integrable models of statistical mechanics.
Much of the relevant information is stored in an explicit H-valued cocycle of
the associated Weyl group, which depends on a set of spectral parameters
as well as on a set of twisting parameters. The twisting parameters
encode the choice of boundary conditions for the associated integrable models.

In the second part of the talk we come to the central object of the talk: the quantum KZ equations.
They form a holonomic system of difference equations acting on spectral parameters.
They are solved by correlation functions of the above mentioned integrable models. I establish
a holonomic extension of the quantum KZ equations by exhibiting an explicit compatible
system of difference equations acting on twisting parameters.
I discuss its application in creating symmetric Laurent polynomial solutions of
quantum KZ equations. This class of solutions is of particular interest due to its
connection with Macdonald polynomials, and its application to the Razumov-Stroganov
conjecture. This is joint work with Michel van Meer.

January 16th, 2009 - **Oratie Gunther Cornelissen**

Tijdstip: 16.15; locatie: Academiegebouw, Domplein, Utrecht

November 14th, 2008 - **GQT colloquium**

The program will be posted as soon as possible

October 27th, 2008 - **DIAMANT meets GQT**

From 27-31 October the workshop "DIAMANT meets GQT" takes place at
the Lorentz Center, Leiden. The first three days are reserved for the
"Studygroup DIAMANT with GQT", and focus on attacking selected open
mathematical problems. In the last two days the "DIAMANT/GQT-symposium"
takes place, where also results on the problems are presented.

The format of the first three days is inspired by that of the yearly
"Studygroup Mathematics with Industry". Monday morning a small number
of problems are presented. Then the participants are partitioned into
groups and work on the the problems until Wednesday afternoon.

September 26th, 2008 - **GQT colloquium Utrecht**

On September 26 (2008), from 11.00-17.00 there will be the first GQT-colloquium of the academic year 2008/2009. It will be held in Utrecht, room 503 of the Buys Ballot Laboratorium, Princetonplein 5 (directions, see http://www.cs.uu.nl/docs/reach/bbl.php ).
Speakers are Bernardo Uribe (Universidad de Los Andes, Colombia, temporarily MPI, Bonn), Michael Polyak (Technion, Israel, temporarily MPI, Bonn) and Gil Cavalcanti (Mathematisch Instituut, Utrecht).

September 18th, 2008 - **Utrecht General Colloquium Talk by Sergey Shadrin (UvA)**

Title: Cohomological Field Theory.
Location and time: Utrecht University, Mathematics Building, room 611; 15:30 - 16:30.

September 10th, 2008 - **Afscheidsvoordracht Dirk Siersma**

Op 10 september a.s. houdt Dirk Siersma zijn afscheidsrede "Leven met Wiskunde" in de Aula van het
Academiegebouw van de Universiteit Utrecht.
Aanvang 16.15 uur.

Na afloop receptie in de Senaatszaal.

Voorafgaand aan het afscheidscollege vindt vanaf 10.30 uur een wetenschappelijk meetkundesymposium plaats in de aangrenzende Faculty Club Helios, Achter de Dom 7A Utrecht.

September 10th, 2008 - **Symposium Meetkunde**

Ter gelegenheid van het emeritaat van Prof.dr. Dirk Siersma.

Lokatie: Faculty Club Helios, Achter de Dom 7A Utrecht (achter het academiegebouw).

Programma:

10.30-11.30 Ontvangst met koffie en thee.

11.00-12.00 Mihai Tibar (Lille): Walk in the forest of Milnor fibrations

Lunch

13.14-14.15 Aad Goddijn (Utrecht): "de hooge gekromde blauwe RUIMTE BEN IK" over de vierde dimensie bij Theo van Doesburg.

14.30-15.30 Duco van Straten (Mainz): The algebra and topology of line singularities.

Na afloop begint om 16.15 uur het afscheidscollege in de Aula van de Universiteit Utrecht, gevolgd door een receptie.

September 3rd, 2008 - **Workshop Sheaves in Geometry and Quantum Theory**

This is to announce a three-day workshop on the interplay between logic, topology/geometry and quantum theory Sheaves in Geometry and Quantum theory ; September 3-5, 2008 Radboud University Nijmegen, the Netherlands ; funded by the Fellowship of Geometry and Quantum Theory (GQT-cluster) and Stichting Compositio Mathematica. For more information click on the header above.

Invited (confirmed) speakers are: Andreas Doering (Imperial College London), Anders Kock (Aarhus), Jaap van Oosten (Utrecht), Erik Palmgren (Uppsala), Pedro Resende (Lisbon), Isar Stubbe (Antwerp), and Steve Vickers (Birmingham)Registration is free, but for logistic reasons, please inform Chris Heunen (heunen@math.ru.nl) if you plan to attend.

July 14th, 2008 - **Minisymposium on "Applications of Noncommutative Geometry" at 5ecm**

Amsterdam, July 14th - 18th, 2008

List of speakers:

**Caterina Consani** (Johns Hopkins)

**Yuri Manin** (MPIM/Northwestern)

**Pedro Resende** (Lisboa)

**Walter van Suijlekom** (Radboud Universiteit)

see also the plenary talk of **Matilde Marcolli** (MPIM)

organizers: Gunther Cornelissen (UU) and Klaas Landsman (RU)

July 7th, 2008 - **Satelite Conference at The Geometric Langlands Program
(7-11 July 2008) **

Satelite Conference at The Geometric Langlands Program from 7 Jul 2008 through 11 Jul 2008.

We intend to bring together leading mathematicians working on the Geometric Langlands Program. The GLP has deep connections with Number Theory, Algebraic Geometry and with subjects from mathematical physics such as Quantization and Conformal Field Theory. Internationally the subject has quickly become a major theme bridging between these fields. The proposed workshop brings together various research communities in pure mathematics and mathematical physics in the Netherlands and intends to promote the GLP as a unifying research theme.Scientific coordinators: E. Frenkel (University of California, Berkeley, USA), G. Heckman (Radboud University Nijmegen, Netherlands), E.J.N. Looijenga (Universiteit Utrecht, Netherlands), E.M. Opdam (UvA, Netherlands)<\p>

June 30th, 2008 - **Satelite Conference Algebraic Geometry (june 30 - july 4)**

Satelite Conference Algebraic Geometry from 30 Jun 2008 through 4 Jul 2008 at the Lorentz Center

Scientific coordinators: E. Looijenga (Utrecht Univ., The Netherlands), B. Edixhoven (Leiden Univ., The Netherlands), G. van der Geer (Amsterdam Univ., The Netherlands)

June 25th, 2008 - **Talks Losev on 24 and 25 june**

Andrey Losev is visiting Amsterdam, and he is going to give two talks:

Tuesday, June 24, 11:00-13:00, room P0.18, Topological quantum mechanics and higher structures in Morse theory

Wednesday, June 25, 11:00-13:00, room P0.18, Berkovits superstring as a topological string (towards the third superstring revolution)

Both seminars will take place at the KdVI, Plantage Muidergracht 24, 1018TV Amsterdam.Visit is supported by the NwoRussian cooperation on Geometry and Singularity Theory in Mathematical Physics.

June 24th, 2008 - **Talk Sedykh on real global singularity theory**

Tuesday, 14.00-15.00 in room 611 of the Mathematics Institute in Utrecht, there will be another session of the Geometry and Topology seminar.

Speaker: V.Sedykh (Moscow)

Title: On some problems of real global singularity theory

Abstract: Let M and N be smooth closed manifolds of dimensions m and n, respectively, with n greater or equal to m. Consider stable smooth mappings from M to N having only singularities of corank 1. We find a complete system of universal linear relations between the Euler characteristics of the manifolds of multi-singularities of mappings under consideration. As an application, we obtain multidimensional generalizations of the Bose theorem on supporting circles of a plane curve.Visit is supported by the NwoRussian cooperation on Geometry and Singularity Theory in Mathematical Physics.

June 23rd, 2008 - **Talk Mueger : Modular Categories**

You are cordially invited to the Seminar Quantum Groups and Applications

Time: June 23, 10:30-12:30

Location: Room D.3.17 in the D building on Nieuwe Achtergracht 129.

Title: Modular Categories

Speaker: Michael Mueger

Roland van der VeenJune 9th, 2008 - **Educational Week on Noncommutative Integration**

In this Educational Week some aspects of noncommutative integration theory associated with von Neumann algebras will be discussed, as well as some of its applications.

June 5th, 2008 - **Oratie Erik Koelink**

Locatie: Radboud Universiteit, Academiezaal Aula, Comeniuslaan 2

Tijdstip: 15:45

May 30th, 2008 - **GQT-Colloquium**

For the program, see **the colloquium website**.

May 28th, 2008 - **Promotie Oliver Lorscheid**

Titel: "Toroidal automorphic forms for function fields"

May 23rd, 2008 - **MATH-PHYS SEMINAR DAY **

Friday May 23,
Universiteit Utrecht, Minnaert buidling, MIN 401

14:00 : **Graeme Segal (Oxford U.)**
*Noncommutative Geometry and Quantum Field Theory.*

15:00 : Coffee break

15:30 : **Christoph Schweigert (Hamburg U.)**
*Bundle Gerbes and Surface Holonomy.*

16:30 : Drinks

April 28th, 2008 - **Promotie Rogier Swierstra**

Titel: "Moduli spaces of cubic hypersurfaces through a period map"

March 28th, 2008 - **GQT-Colloquium**

Speakers:

Gunther Cornelissen (U Utrecht): Riemann surfaces and spectral triples

Abstract: I will show how to associate to a compact hyperbolic Riemann
surface a finite-dimensional noncommutative Riemannian geometry (a.k.a.
finitely summable spectral triple), such that the zeta functions on the
noncommutative side capture the complex structure of the Riemann surface.
The construction passes via Schottky uniformization and can be seen as a
reformulation of an ergodic rigidity theorem a la Mostow in terms of
spectral triples. (joint work with Matilde Marcolli, arxiv:0708.0500)

Duco van Straten (U Mainz): Classical and Quantum integrability

Abstract: In the talk I will discuss the following question:
Given a classsical integrable system defined by
n Poisson commuting polynomials, can one find commuting \hbar-differential
operators whose symbols are the
given polynomials?

Markus Reineke (U Wuppertal): Poisson automorphisms and quiver moduli

Abstract: We discuss a factorization problem for Poisson automorphisms of a formal
plane, which turns out to involve invariants for moduli spaces of quiver
representations. This factorization problem appears in recent work of
Kontsevich and Soibelman on Donaldson-Thomas invariants of noncommutative
Calabi-Yau manifolds. We sketch a proof involving quiver realizations of
quantized Kac-Moody algebras.

Location: Linnaeus building, zaal Lin4

Schedule:

10:45: Coffee and Tea

11:00: G. Cornelissen

12:00: Uitreiking scriptieprijs door W.v.d. Kallen

aansluitend: Jozef Steenbrink met medelingen namens de directeur

14:00: D.v.Straten

15:00: Coffee and tea

15:15: M. Reineke

16:15- : Reception in the Huygens building

February 11th, 2008 - **Polynomial Mappings: Algebra, Computation and Topology: Febuary 11 and 12, 2008 **

Workshop Polynomial Mappings: Algebra, Computation and Topology

Febuary 11 and 12, 2008 at the Huygens Building, Radboud University Nijmegen (The Netherlands)

These 2 days meeting will concentrate on new methods of algorithmic methods in the geometry and topology of polynomial mappings, both local and global. Special attention will be given to topics as behaviour at infinity, the structure of the bifurcation diagram, monodromy around a given stratum, mixed Hodge structures of fibres, algebraic coumputation of topological invariants, Cohen Macaulay modules, Lie algebras of algebraic varietes and singularities, geometry of quadratic mappings and various versions of Keller Jacobian conjecture.

Please register

February 8th, 2008 - **Oratie Erik van den Ban**

16.15 uur, Academiegebouw Universiteit Utrecht

February 1st, 2008 - **GQT-Colloquium, University of Utrecht, Minnaert building room 211**

11:15-12:15
Vladimir Kazakov, ENS, Paris VI:

Integrable quantum (super)spin chains and discrete classical
dynamics.

12:15 - 13:30 Lunch

13:30 - 14:30
Erik Koelink, RU, Nijmegen:

Quantum groups and the quantum group analogue of
SU(1,1).

14:30 - 14:40 Dirk Siersma: News from the GQT board.

14:40 - 15:00 Coffee & Tea.

15:00 - 16:00
Nick Dorey, DAMTP, Cambridge:

Integrability and the AdS/CFT correspondence.

16:00 - ?? Drinks

Abstracts:

Vladimir Kazakov, ENS, Paris VI

Title: Integrable quantum (super)spin chains and discrete classical
dynamics.

We review a discrete classical dynamics approach to the
integrable quantum (super)spin chains. It takes a different venue from
the well known algebraic Bethe ansatz but it also allows to go all the
way from the definition of the R-matrix to the final system of nested
Bethe equations. The intermediate steps include the derivation of the
determinant Bazhanov-Reshetikhin formula and the associated integrable
discrete bilinear Hirota equation describing the quantum fusion of
representations, the solution of this equation by the Backlund
transformation and the general formulas for transfer-matrices in terms
of Baxters Q-functions. The method looks especially useful in the case
of supergroups where the new bilinear relations among Q-functions are
observed.

Erik Koelink, RU, Nijmegen

Title: Quantum groups and the quantum group analogue of
SU(1,1).

Quantum groups originated in the 1980ies from
different perspectives. It took quite some time
before a satisfactory general theory
for non-compact quantum groups was established.
A general theory on the level of operator algebras for
quantum groups has been introduced in 2000 and 2003 by Kustermans
and Vaes. We review their definition and main results, and
we consider the example of the quantum group analague of the
normalizer of SU(1,1) in SL(2,C).

Nick Dorey, DAMTP, Cambridge

Title: Integrability and the AdS/CFT correspondence.

I will review recent progress towards a solution of N=4 SUSY
Yang-Mills theory in the planar limit and related developments in the
dual string theory on AdS_5 x S5.

January 29th, 2008 - **January 31st, 2008: Workshop on Integrability in the AdS/CFT correspondence**

January 25th, 2008 - **Workshop on McKay correspondence for symplectic resolutions (following Bezrukavnikov-Kaledin) **

(January 25-26, joint with the group of H. Esnault and E. Viehweg, University Duisburg-Essen and M. Lehn, Universtiy Mainz)
The aim of the Workshop is to understand the proof, due to Bezrukavnikov
and Kaledin (McKay equivalence for symplectic resolutions of quotient
singularities, arXiv:math/0401002), of a higher dimensional
generalization of the so called McKay correspondence. This proof uses a
rather large variety of ideas, so we hope that the proof itself might be
as interesting as the result.

January 23rd, 2008 - **Speaker Maxim Kazarian**

Maxim Kazarian (Steklov Mathematical Institute, Moscow) will his second talk in the geometry-topology seminar in Utrecht on wednesday january 23 : 14.00-15.00 room 611B Math Institute.

This talk is a continuation of his lecture on wednesday january 23

Title: Moduli spaces, Hurwitz numbers, and integrable hierarchies (2).

Abstract: see announcement for janary 16

January 16th, 2008 - **Speaker Maxim Kazarian**

Maxim Kazarian (Steklov Mathematical Institute, Moscow) visits the Department of Mathematics of Utrecht University from january 9 until february 2, 2008. He will give a series of 2 talks in the geometry-topology seminar in Utrecht:

wednesday january 16 : 14.00-15.00 room 611B Math Institute

wednesday january 23 : 14.00-15.00 room 611 B Math Institute

Title: Moduli spaces, Hurwitz numbers, and integrable hierarchies.

Abstract: The famous ELSV (Eckedah-Lando-Shapiro-Vainstein) formula relates two theories: the Hurwitz theory of enumerating ramified coverings of a sphere and intersection theory on the moduli spaces of curves. It provides on of the most natural and straightforward explanation of the relationship between intersection theory on moduli spaces and integrable hierarchies discovered by physicists. Starting from the ELSV formula, we derive a number of new equations on the generating functions for Hodge integrals over the moduli space of complex curves. This gives a new simple and uniform treatment of certain known results on Hodge integrals like Witten's conjecture, Virasoro constrains, Faber's $\l_g$-conjecture etc. Among other results we show that a properlyarranged generating function for Hodge integrals satisfies the equations of the KP hierarchy.

Framework : NWO-RFBR-Project : Geometry and Singularity Theory in Mathematical Physics

December 14th, 2007 - **Intercity Seminar Algebra and Geometry**

Free University of Amsterdam, W&N Building

11:00-12:45, Room KC 137

Daniel Huybrechts: *Derived equivalences and stability conditions (mainly for K3 surfaces)*

14:00-15:45, Room S 111

Michel van den Bergh: *3-dimensional flops and non-commutative algebras*.

*In the evening of the 14th we plan to have dinner in Amsterdam with the speakers. If you want to join us, please let me know (bmoonen at science.uva.nl), preferably before Wednesday 12 December.*

December 12th, 2007 - **2007 Twente Conference on Lie Groups: Dec 12-14**

The 2007 Twente Conference on Lie Groups will take place on December 12-14, 2007 at Twente University

Organizer : Gerard Helminck

V. Golovko, D. Gurevich, A.G. Helminck, E. Horozov, M. Iorgov, M. Kazarian, A. Khoroshkin, S. Khoroshkin, S. Lando, A. Marshakov, O. Morozov, Yu. Neretin, A. Unterberger.

To register for the 2007 Twente Conference on Lie Groups, please send an e-mail to Gerard Helminck: helminckgf@ewi.utwente.nl

November 30th, 2007 - **GQT-Colloquium**

KdV Institute room P.227

11:15-12:15 Elmar Schrohe: Index Theory for Boundary Value Problems via Continuous Fields of C*-algebras.

13:30-14:30 Eric Rains: Elliptic hypergeometric integrals

15:00-16:00 Claus Hertling: Oscillating integrals and tt* geometry.

November 29th, 2007 - **Speaker: Claus Hertling **

Geometry and Topology seminar: Time: 11.00, Location: Room 611B

Speaker: Claus Hertling (Mannheim, Germany)

Title: Distinguished bases and Stokes matrices for the simple and the simple-elliptic singularities.

November 23rd, 2007 - **Intercity Seminar Algebra and Geometry**

University of Amsterdam,
KdV Institute (= Euclides building, = Building P)

11:00-12:45, Room P 0.17

Jan Stienstra: *Stability conditions*

14:00-15:45, Room P 2.27

Eduard Looijenga: *The Bondal-Orlov conjecture, and Bridgeland's theorem for 3-folds*

November 2nd, 2007 - **Intercity Seminar Algebra and Geometry**

Radboud University Nijmegen,
Huygens Building, Room HG00.310

11:00-12:45

Jochen Heinloth: *Semi-orthogonal decompositions and t-structures*

14:00-15:45

Alex Quintero: *The McKay correspondence*

October 12th, 2007 - **Intercity Seminar Algebra and Geometry**

Leiden University

11:00-12:45, Gorlaeus Laboratory, Room 03

Ben Moonen: *Orlov's theorem and reconstruction results*

14:00-15:45, Snellius Building, Room 174

Jozef Steenbrink: *An introduction to the minimal model program*

September 28th, 2007 - **Intercity Seminar Algebra and Geometry**

The IC-seminar Algebraic Geometry is devoted to Derived categories and stability conditions will meet in Utrecht:

11:00-12:45 Bas Edixhoven: General Introduction

14:00-15:45 Gerard van der Geer: Mukai's results for abelian varieties and K3 surfaces

Location: Buys Ballot Laboratory , Room BBL 106, For more information see the seminar list or click on the header.September 28th, 2007 - **promotie Rogier Bos**

On Friday 28 September, 15:30, Rogier Bos will defend his thesis at the Radboud University Nijmegen with the title "Groupoids in Geometric Quantization".
Promotor: Prof. dr. Klaas Landsman.
Before the ceremony there will be a small symposium with three talks:
10:00-10:45 Jean Renault (Orleans): Cartan subalgebras in C*-algebras
11:00-11:45 Gijs Tuynman (Lille): The Lagrange formalism: a human mistake?
14:00-14:45 Ieke Moerdijk (Utrecht): Lie algebroids and the Milnor-Moore Theorem
The talks will be in room HG 00.065.

September 27th, 2007 - **Farewell symposium Rainer Kaenders**

Dr. Rainer Kaenders wordt per 1 oktober hoogleraar in
Keulen, en zal Nijmegen dus verlaten. Zijn vertrek zal
worden opgeluisterd met een Wiskunde Onderwijs
middag.
Programma:
15:00 uur: Ontvangst met koffie en thee in de hal
van het Huygensgebouw
15:45–17:30: Voordrachten in HG00.303
Prof. dr. Jan van de Craats, Het nieuwe rekenen
Drs. Aad Goddijn, Het misverstandWiskunde
Dr. Leon van den Broek, Het beweegt
17:30–19:00: Borrel in de vide van het Huygensgebouw

September 19th, 2007 - **Day on Algebraic Topology in Utrecht**

On September 19, a small symposium will be held on topics in Algebraic Topology.

9.45 - 10.00 : Coffee

10.00 - 11.00 : Kathryn Hess (Lausanne): "Koszul complexes and
homotopy morphisms"

11.15 - 12.15 : Tom Leinster (Glasgow): "Homotopy algebras for operads"

Lunch

14.00 - 15.00 : Jiri Rosicky (Brno): "Combinatorial model categories"

Tea

15.30 - 16.30 : Clemens Berger (Nice): "The lattice path operad"

The lectures will take place in BBL (Buys-Ballot Lab) , zaal 361. All interested are welcome to attend!

September 18th, 2007 - **Promotie Ittay Weiss**

Ittay Weiss will defend his thesis
"Dendroidal Sets" at 14.30 in the Academiegebouw
Promotor is Prof.dr. I. Moerdijk.

September 14th, 2007 - **GQT-Colloquium
**

GQT colloquium, and kickoff of the Intercity Seminar on "Derived categories and stability conditions"

Friday September 14th, 2007; 10:30 t/m 18:00

Location: RU Nijmegen, Huygensgebouw and Linnaeusgebouw

Speakers:

Richard Thomas (Imperial College, London)

Lutz Hille (Univ. Bielefeld)

Eric Opdam (UvA)

Schedule

10:30 - 11:00 Coffee

11:00 - 12:15 Lutz Hille: Strongly exceptional sequences of line bundles on toric varieties, Huygensgebouw, HG00.062

12:15 - 14:00 Lunch break

14:00 - 15:15 Eric Opdam: Category O for rational Cherednik algebras, Linnaeusgebouw, N6

15:15 - 15:30 Coffee

15:30 - 16:45 Richard Thomas: Counting curves and stability of ideal sheaves, Linnaeusgebouw, N6

16:45 - 18:00 Reception

August 20th, 2007 - **Geometric Aspects of Analysis and Mechanics, Hans Duistermaat 65th Birthday Conference**

time: August, Monday 20 through Friday 24, 2007

Speakers include: Michael Atiyah, Nicole Berline, Jean-Michel Bismut, Yves Colin de Verdière, Richard Cushman, Nils Dencker, F. Alberto Grunbaum, Victor Guillemin, Tara Holm, Lisa Jeffrey, Eugene Lerman, Eckhard Meinrenken, Jiang-Hua Lu, Richard Melrose, Paul-Emile Paradan, Isadore Singer, Reyer Sjamaar, Johannes Sjöstrand, Gunther Uhlmann, San Vũ-Ngọc, Alan Weinstein

More info: see website

June 28th, 2007 - **Talk Christian Blohmann: Differentiable stacks and noncommutative geometry**

Christian Blohmann (University of California, Berkeley) will speak on

`Differentiable stacks and noncommutative geometry'

Room: K8B (Basement Mathematics Building)

Date and time: Thursday, June 28, 10:00 - 11:00 am.,

Abstract: Differentiable stacks and noncommutative geometry are alternative methods to study geometric situations which are considered to be pathological in the sense of ordinary differential geometry, such as non-smooth quotients of differentiable manifolds or singularities of gauge fields. I will show how viewing these two approaches as dual to each other leads to a generalization of Hopf algebras and to Lie theory on differentiable stacks.

June 26th, 2007 - **Talk Sergey Shadrin: Givental symmetries of tautological equations.
**

Dr Sergey Shadrin (Universität Zürich) speaks Tuesday June 26 11:00-12:00 in Room K8b on

Givental symmetries of tautological equations.

Abstract: I am going to dicsuss the system of PDEs that is called tautological equations. It comes from relations among natural classes in the cohomology of the moduli spaces of curves, and it can serve as a system of axioms for the correlators of topological conformal field theory. This system of PDEs has a huge group of symmetries that was discovered by Givental in genus 0. He proposed to quantize its action, and it was proved by Faber, myself, and Zvonkine that the quantized action also preserves the whole system of tautological relations in all genera.

June 20th, 2007 - **Talk Boris Shoikhet:
"Koszul duality in deformation quantization"
**

Boris Shoikhet (Univ de Luxembourg) will speak on Wednesday June 20 (14:00-15:00) in Room K8b on

"Koszul duality in deformation quantization",

Abstract: Let alpha be a polynomial Poisson bivector on a vector space V. Then Kontsevich constructs a star-product f * g on S(V^*), polynomial functions on V. We construct from alpha another algebra by generators and relations. We prove that this algebra obeys the Poincare-Birkhoff-Witt property. Even in the classical case we found a new, cohomological, proof of the PBW theorem, which shares some light on this theorem. We conjecture that the constructed algebra is isomorphic to the Kontsevich star-algebra. We discuss this conjecture, and its relation on our recent preprint math.0706.1333 on an explicit construction of the Quillen localization.

June 14th, 2007 - **Talk Sergey Natanzon : Singularities and noncommutative Frobenius manifolds**

Thursday June 14 from 13:00-14:00 in K11 there is a talk:

Speaker: Sergey Natanzon (Independent University Moscow)

Title: Singularities and noncommutative Frobenius manifolds

Abstract: We prove that quaternion miniversal deformations of the A_n singularity possess a structure of noncommutative Frobenius manifold in the sense of an extended cohomological field theory.

June 7th, 2007 - **From Tate Curves to Zariski-Riemann Spaces: A Crash Course in Rigid Geometry by Fumiharu Kato (Kyoto)**

This series of lectures provides an introduction to rigid geometry with special emphasis on its birational-geometric aspects.

Rigid geometry, often spelled as rigid analytic geometry, is an algebro-geometric framework that allows one to mimic the usual analytical approach to varieties over the complex numbers for varieties defined over, say, p-adic fields. The typical `analytical' features of rigid geometry can be seen in Tate's uniformization of elliptic curves, the so-called Tate curves, in which certain infinitudes, such as quotient by infinite groups, infinite power series, etc., make perfect sense. Later, M. Raynaud discovered that rigid geometry has a strong relationship with the geometry of formal schemes.

Even after this historic shift from analytic geometry to algebraic geometry, rigid geometry still suffered from a serious deficiency of `visualization', which would bring an intuitive understanding of the spaces that appear. The original rigid geometry failed to have a correct notion of `points'. The correct `points', have been found independently by several people, such as R. Huber and K. Fujiwara. Fujiwara's theory, in particular, takes up Zariski's viewpoint of classical birational geometry, and provides the desired visualization by a formal geometric analogue of the so-called Zariski-Riemann spaces.

**Plan for the lectures**

(1) Introduction: Tate curves;

(2) Playing around with the analytic projective line;

(3) Rigid geometry by Tate and Raynaud;

(4) Coherent topological spaces and valuative topological spaces;

(5) Zariski's birational geometry;

Nagata's embedding theorem;

Flattening theorem;

(6) Formal geometry and rigid geometry: Zariski-Riemann triple;

(7) GAGA.

**Schedule**
The five lectures take place from 10--12 a.m. in room K8b (basement) of the Mathematical Institute of the University of Utrecht on the following days:
Thursday 7th,
Tuesday 12th,
Thursday 14th,
Tuesday 19th,
Thursday 21st
of June, 2007.

Everybody is welcome! More information: contact Gunther Cornelissen at cornelis@math.uu.nl.

June 7th, 2007 - **Talk by Raf Blockland: An introduction to Calabi Yau Algebras**

Raf Bocklandt (Universiteit Gent)
will talk this Thursday, June 7, 10:00-11:00 in Utrecht Room M204 (Minnaert
Building) on:
An introduction to Calabi Yau Algebras.
Abstract:
We will show how Calabi Yau Algebras naturally turn up
in geometrical problems connected to Kleinian Singularities and String
theory.
Also we will give some classification results for these algebra

June 4th, 2007 - **Nijmegen Singularity Days, June 4th-5th**

Organizers: Dirk Siersma, Joseph Steenbrink

This workshop will also be a meeting point of the

* INTAS project “Singularities, Bifurcations and Monodromy”

* NWO – Russia project “Geometry and Singularity Theory in Mathematical Physics”

The workshop is funded by these projects and has additional funding from the Mathematical Research Institute MRI and the Fellowship for Geometry and Quantum Theory GQT.

May 31st, 2007 - **Nijmegen Geometry Days May 31th-June 2nd (in honour of Joseph Steenbrink)**

In honour of Joseph Steenbrink on his 60th birthday.

**Speakers:
**Robbert Dijkgraaf, Amsterdam

Luc Illusie, Parijs

Theo de Jong, Mainz

Eduard Looijenga, Utrecht

Andras Nemethi, Columbus

Frans Oort, Utrecht

Chris Peters, Grenoble

Morihiko Saito, Kyoto

Duco van Straten, Mainz

Orsola Tommasi, Hannover

Claire Voisin, Parijs

Steve Zucker, Baltimore

**Scientific Commitee:**

Gerard van der Geer, Amsterdam

Gert Heckman, Nijmegen

Eduard Looijenga, Utrecht

Ben Moonen, Amsterdam

Dirk Siersma, Utrecht

**Local Organisers:**

Gert Heckman, G.Heckman@math.ru.nl

Frans Clauwens, F.Clauwens@math.ru.nl

Roel Willems, R.Willems@math,ru.nl

**Secretary:**

Greta Oliemeulen, maths@math.ru.nl

024-3652986

All lectures will be held in the Huygens Building (HG00.307) of the Radboud University of Nijmegen.

May 10th, 2007 - **A. Gorinov in UU geometry and topology seminar NOTE: 10/5**

**Title:**Rational cohomology of the moduli spaces of pointed genus 1 curves

**Time:** Thursday May 10, 14:00-15:00

**Place:** Room 611B of the Mathematics Building, Utrecht

April 26th, 2007 - **S. Duzhin in UU geometry and topology seminar 26/4**

**Title:** Geometrization conjecture and Perelman's work

**Time:** Thursday April 26, 14:00-15:00

**Place** Room 611B of the Mathematics Building, Utrecht

April 19th, 2007 - **Special Seminar talk by Konstantin Styrkas 19/4 at UU
**

**Title:** Resonance relations, holomorphic trace functions and
hypergeometric solutions to qKZB equations.

**Time:** Thursday April 19, 10:00-11:00

**Place:** Room 611B of the Mathematics Building, Utrecht

April 13th, 2007 - **Joint Math-Physics seminar in Utrecht **

Program:

14:00 Vicente Cortes (Univ. Hamburg)

**Title: Cones over pseudo-Riemannian manifolds**

Abstract: By a classical theorem of Gallot (1979), a Riemannian cone over a
complete Riemannian manifold is either flat or has irreducible holonomy. We
consider metric cones with reducible holonomy over pseudo-Riemannian
manifolds and obtain local and global structure theorems.

15:00 Coffee Break

15h15 J. Stienstra (Univ. Utrecht)

**Title: Geometric structures related to AdS/CFT**

Abstract: I will discuss connections (found in physics papers) between
Sasaki-Einstein 5-folds on the one hand and quivers on the other hand.
This will also involve intrigueing viewpoints on zero loci of 2-variable
Laurent polynomials.

16:15 Borrel

March 26th, 2007 - **Conference in honour of Richard Cushman (March 26-30)**

March 23rd, 2007 - **GQT colloquium (Amsterdam).
Speakers: S. Kato, E. Looijenga, B. Nienhuis.**

** Location:**
University of Amsterdam, KdV Institute for Mathematics,
Plantage Muidergracht 24, lecture room P.017.

** Program:**

**11.15-12.15** Bernard Nienhuis (UvA)

Title: Statistical lattice models on a cylinder.

**12-15-13.30** Lunch

**13.30-14.30** Syu Kato (University of Tokyo, Japan)

Title: An exotic Deligne-Langlands correspondence for symplectic groups.

**14.30-15.00** Coffee and tea.

**15.00-16.00** Eduard Looijenga (UU)

Title: The moduli space of curves---a meeting point of algebraic geometers and geometric topologists.

**16.00--** Reception

March 19th, 2007 - **Conference on Combinatorics and Physics**

Date: **March 19-23, 2007**

If you want to participate please send a short message to: combphys07@mpim-bonn.mpg.de

More information: see website

March 9th, 2007 - **Symposium at the closing of the FOM/GBE programme on Mathematical Physics (speakers include Atiyah, Penrose, Yoccoz, Werner)**

On 9 March 2007 the FOM/GBE programme Mathematical Physics will end
festively with an international symposium in the Keizersgrachtkerk in
Amsterdam.

Speakers include **Sir Michael Atiyah, Sir Roger Penrose,
Jean-Christophe Yoccoz** and **Wendelin Werner**.

The final programma will be announced mid-January.
Registration will open around that time too.
More information can
be found in due time on the FOM-website.

March 6th, 2007 - **Two talks in Amsterdam (KdV); speakers Vicor Nistor and Ralf Meyer**

On March 6 Victor Nistor and Ralf Meyer will each give a talk at the KdV institute. The program is as follows:

15-16: Victor Nistor (Penn State University),

Title: "Analysis on Lie manifolds, well posedness on polyhedral domains, and optimal rates of convergence".16-17: Ralf Meyer (Georg-August-Universitt Goettingen),

Title: Embeddings of derived categories.Place: Room 3.85, building J/K Valckenierstraat 65, 1018 XE Amsterdam.

February 22nd, 2007 - **Utrecht General Colloquium talk by Arthemy Kiselev (IHES):
Pre-Hamiltonian formalism for integrable nonlinear systems**

15:00 (Eigenruimte) Tea/Coffee and cookies

15:3--16:30 (K11) General Mathematical Colloquium

**Arthemy Kiselev**(IHES):

*Pre-Hamiltonian formalism for integrable nonlinear systems*

February 22nd, 2007 - **Lecture by Yuri Berest (Cornell University and IHES)**

in the UvA Representation Theory Seminar.

**Title:** Ideals of rings of differential operators on algebraic curves.

**
Time:**
11.00-12.00

**
Location:** Amsterdam, KdV Institute, room P.016.

February 9th, 2007 - **GQT colloquium RU (Nijmegen); Speakers: Bunke, Marcolli, Meyer**

For further information see the GQT colloquium
page.

February 1st, 2007 - **Utrecht General Colloquium talk by Eric Opdam (UvA): Euler-Poincare formula for tempered characters of affine Hecke algebras**

15:00 (Eigenruimte) Tea/Coffee and cookies

15:30--17:15 (Minnaert 211) General Mathematical Colloquium

**Eric Opdam**(UvA):

*Euler-Poincare formula for tempered characters of affine Hecke algebras*

part 1: The Plancherel formula for Hecke algebras: motivation and basic results

part 2: Index functions and formal dimensions

part 1: The Plancherel formula for Hecke algebras: motivation and basic results

part 2: Index functions and formal dimensions

January 18th, 2007 - **Utrecht General Colloquium talk by Walter van Suijlekom (RU): Renormalization of gauge fields: A Hopf algebra approach**

15:00 (Eigenruimte) Tea/Coffee and cookies

15:3--16:30 (K11) General Mathematical Colloquium

**Walter van Suijlekom**(RU):

*Renormalization of gauge fields: A Hopf algebra approach*

December 13th, 2006 - **The 2006 Twente conference on Lie groups**

From 13-15 December 2006 the annual Twente conference on Lie groups takes place.
For more information contact Gerard Helminck
by sending an email to helminckgf@cs.utwente.nl

November 30th, 2006 - **J. Martens (MPI) in Utrecht**

J. Martens will speak in the geometry and topology seminar.

Title: Equivariant volumes of non-compact quotients and instanton counting

Location and time: 14:00-15:00 in room 611a in the math building

November 28th, 2006 - **Mini-workshop on index theory of singular spaces**

Location: RU Nijmegen, Huygens Building (FNWI)

**Tuesday 28/11**

10:45- 12:00 **Walter van Suijlekom** (MPIM), *Local index formula for SU_q(2)*

Location: HG01.057

13:45-14:30 & 14:45-15:30 **Varghese Mathai** (Adelaide) *Twisted index theory on orbifolds I+II*

Location: HG01.057

16:00-17:15 **Hessel Posthuma** (Utrecht) *Cyclic homology theory of deformations
over orbifolds*

Location: HG01.057

**Wednesday 29/11**

10:15 - 11:30 **Markus Pflaum** (Mainz) *Algebraic index theory and deformations
over orbifolds*

Location: HG03.084

12:45-13:30 & 13:45-15:00 **Varghese Mathai** (Adelaide) *Twisted index theory on orbifolds III+IV*

Location: HG02.032

**Note!** All talks are meant for an audience with good knowledge of index
theory, K-theory and noncommutative geometry

November 24th, 2006 - **GQT-Colloquium**

joint meeting of the GQT-Colloquium and the Utrecht joint seminar on mathematical physics

14:00-15:00 **Varghese Mathai** (Adelaide), *T-duality in a background H-flux*

Abstract.This talk will be concerned with global aspects of T-duality on compactified spacetimes that are torus bundles, in the presence of a topologically nontrivial background H-flux. The characterization of when exactly the T-dual is another torus bundle with H-flux will be discussed. Global, nonclassical spacetimes will be proposed in the other cases, and justified. Finally, the current status of this theory will be outlined.

15:15-16:15 **Erik Verlinde** (UvA), *Strings, Symmetric Products and the Elliptic Genus*

16:20-???? reception

Location: UU Mathematics Building, room K11

November 23rd, 2006 - **Colloquium Lecture by Varghese Mathai**

15.30-16.30

Utrecht Colloquium lecture

**Varghese Mathai** (Adelaide): *On a curious extension of the Atiyah-Singer index theorem*

Location: room K11, Mathematics Building

November 20th, 2006 - **Mathai Varghese at UvA
**

Mathai Varghese (Adelaide, Australia) will give a talk at the KdVI institute on his recent work with Melrose and Singer on index theory (math.DG/0402329 + followup work).

Time: Monday November 20, from 11-12,

Room: P0.19 (gebouw Euclides, Plantage Muidergracht 24),

Title: Fractional Analytic Index.

November 16th, 2006 - **Colloquium lecture by J.D. Lewis**

15.30-16.30

Utrecht Colloquium Lecture

**J.D. Lewis** (Alberta): *Variants of the cycle class map*

Location: room K11, Mathematics Building

November 9th, 2006 - **UU Topology & Geometry lecture by E. Emsiz (UvA)**

14.00-15.00 Room 611a mathematics building

**Title:**
Affine Weyl groups and integrable systems with delta potentials

October 13th, 2006 - **IMAPP Symposium ``The Origin of the Universe: Mathematics, Astrophysics or Particle Physics?''**

One of the most spectacular scientific symposia ever held in The Netherlands will take place on Friday, October 13th at the FNWI in Nijmegen. This is the IMAPP-Symposium (IMAPP being the Institute for Mathematics, Astrophysics and Particle Physics within the Faculty of Science).

The speakers at the symposium are:

Hans Küng (Theologian, author of numerous books) |

Roger Penrose(Winner of the Wolf Prize, Mathematician and
Cosmologist) |

Gerard 't Hooft (Nobel Laureate in Physics 1998) |

Jos Engelen (Director of CERN) |

Don Zagier (Director of the Max-Planck-Institute for Mathematics,
Bonn) |

Rajiv Sunyaev (Director of the Max-Planck-Institute for
Astrophysics, Garching) |

Registration via the website is strictly necessary!

October 10th, 2006 - **Scientific Meeting at the Cluster Opening**

Time: 13:00-16:00

Location: Belle van Zuylenzaal, Academiegebouw Utrecht

Speakers:

13:30-14:30 Pierre Cartier (IHES, France) Towards a "cosmic Galois group": two parallel hierarchies of polyhedra and their meaning for number theory and quantum field theories |

15:00-16:00 Alan Weinstein (UC Berkeley, USA) The quantum torus as a quantum "group" |

Registration via NWO-website is required!

October 10th, 2006 - **Official opening ceremony of the GQT-cluster by Minister of Education**

Time: 16.00-17.30

Location: Senaatszaal, Academiegebouw Utrecht

Meeting of the Mathematical Clusters at the occasion of the official opening of the GQT-cluster by the Minister of Education, Culture and Science.

Followed by drinks at 17:30

Registration via NWO-website is required!

October 8th, 2006 - **Modular forms, October 8-13**

The topic of the conference is the theory of modular forms, both the geometric as well as the arithmetic aspects.

Expected participants include: Bergström, Boecherer, Bosman, Bruinier, Diamond, Edixhoven, Faber, van der Geer, Gritsenko, Grushevski, Ibukiyama, R. de Jong, Katsura, Kondo, Kudla, Meagher, Moonen, Pollack, Rajan, Rastegar, Salvati-Manni, Savin, Shepherd-Barron, Taelman, Wiese, Zagier.

The conference is held at the traditional Hotel van der Werff on Schiermonnikoog island, the Netherlands.

September 28th, 2006 - **Symposium "Geometry in Autumn" (September, 28th-29th)**

This short symposium at the Lorentz Centre in Leiden is devoted to recent developments in complex algebraic geometry. Some of the topics the symposium focuses on are moduli spaces, algebraic curves and surfaces, and vector bundles. We will also look back and evaluate the developments since the symposium 'Geometry in Autumn I' held about ten years ago on the occasion of the retirement of Van de Ven.

Speakers: E. Amerik, W. Barth, A. Beauville, F. Catanese, G. Deschamps, G. Farkas, K. Hulek.

Lectures will start on Thursday September 28 at 2 pm. The symposium will end in the early afternoon of Friday.

Participants are requested to register at the Lorentz Center.

Organizers: Bas Edixhoven, Gerard van der Geer Martin Luebke

September 22nd, 2006 - **Lectures by Jan Stienstra and Vasily Golyshev**

Intercity Number Theory Seminar

13:00-14:00 **Vasily Golyshev** (Moscow), *Spectra and Their Arithmetic *

14:15-15:15 **Jan Stienstra** (Utrecht), *Apery-like numbers, differential equations of type DN and dimer models*

Location: UU Mathematics Building, room K11

September 20th, 2006 - **Lecture by Alessio Corti**

16.15-17.15

Lecture

** Alessio Corti** (Imperial College): * Orbifold quantum cohomology of Fano toric stacks*

Location: room K11, Mathematics Building

January 1st, 1970 -

January 1st, 1970 -