# Events

# Events 2013

**Workshop on Algebraic Cycles and Tautological classes
**

*December 17th, 2013*

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)

**Belgian-Dutch Algebraic Geometry Day
**

*November 22nd, 2013*

**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.

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

*November 21st, 2013*

**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)

**Higher Geometric Structures along the Lower Rhine III
**

*October 17th, 2013*

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)

**Workshop Noncommutative Geometry and Particle Physics, Leiden\
**

*October 14th, 2013*

Lorentz Center Leiden, October 14-18, 2013.

**Topics:**

- The Higgs Sector and its Experimental Status
- Phenomenology of Electroweak and Strong Forces
- The Noncommutative Standard Model
- Particle Physics: Beyond the Standard Model
- Family Structure of Particle Physics
- Gravity and Noncommutative Geometry

**Scientific organizers:**

- Thijs Van den Broek (Nijmegen, The Netherlands)
- Alain Connes (Bures-sur-Yvette, France)
- Jose Gracia-Bondia (Zaragoza, Spain)
- Piet Mulders (Amsterdam, The Netherlands)
- Walter Van Suijlekom (Nijmegen, The Netherlands)

**Workshop Knots & Physics, Amsterdam
**

*September 27th, 2013*

**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

**Workshop “Elliptic Integrable Systems and Hypergeometric Functions”
**

*July 15th, 2013*

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

**A singular life – Conference in honour of Eduard Looijenga
**

*June 27th, 2013*

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. Dieudonn�, 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)

**G&T day – Utrecht
**

*June 21st, 2013*

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.

**Mini Workshop on locally analytic representations and some applications
**

*June 5th, 2013*

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).

**Topology & Geometry Day on the occasion of Maria Amelia Salazar’s Ph.D. defense
**

*May 23rd, 2013*

**GQT colloquium Utrecht
**

*May 17th, 2013*

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?

**Workshop “Moduli of curves and integrable hierarchies”
**

*April 26th, 2013*

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!

**Operations on Hochschild complexes, revisited
**

*March 28th, 2013*

**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.

**GQT colloquium Nijmegen
**

*March 1st, 2013*

**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.