**Topics around algebraic and symplectic geometry as well as mirror symmetry**

This colloquium invites mostly external speakers. It is funded by the Emmy Noether grant "Degenerations of Calabi-Yau Manifolds and Related Geometries" of Helge Ruddat.

**We meet during the semester from 13.00 - 13:50 in Hilbertraum 05-432 (JGU Mainz, Mathematisches Institut, Staudingerweg 9, 55099 Mainz).**

**Program**

03.11.2016 13:00 Tom Sutherland (Università degli Studi di Pavia)

*Stability conditions from periods of elliptic curves*

19.07.2016 13:00 Tim Kirschner (Universität Duisburg-Essen)

*Finite quotients of three-dimensional complex tori*

14.07.2016 14:00 James Pascaleff (University of Illinois)

*Symplectic Cohomology and Wall Crossing*

26.04.2016 13:00 Mohammad Akhtar (Imperial College London)

* Mirror symmetry and the classification of Fano varieties*

07.01.2016 12:00 Andreas Gross (Universität Kaiserslautern)

*Intersection Theory on Tropicalizations of Toroidal Embeddings*

17.12.2015 12:00 Sara Filippini (Universität Zürich)

*Refined curve counting and the tropical vertex group*

29.10.2015 12:00 Aleksey Zinger (MPIM Bonn)

*Normal Crossings Divisors for Symplectic Topology*

25.06.2015 12:00 Peter Overholser (Leuven/Imperial College London)

*Descendent tropical mirror symmetry for P2*

## Abstracts

- 03.11.2016 13:00 Tom Sutherland: Stability conditions from periods of elliptic curves
- 19.07.2016 13:00 Tim Kirschner: Finite quotients of three-dimensional complex tori
- 14.07.2016 14:00 James Pascaleff: Symplectic Cohomology and Wall Crossing
- 26.04.2016 13:00 Mohammad Akhtar: Mirror symmetry and the classification of Fano varieties
- 07.01.2016 12:00 Andreas Gross: Intersection Theory on Tropicalizations of h3 Embeddings
- 17.12.2015 12:00 Sara Filippini: Refined curve counting and the tropical vertex group
- 29.10.2015 12:00 Aleksey Zinger: Normal Crossings Divisors for Symplectic Topology
- 25.06.2015 Peter Overholser: Descendent tropical mirror symmetry for P2

### 03.11.2016 13:00 Tom Sutherland: Stability conditions from periods of elliptic curves

I will describe spaces of stability conditions on some Calabi-Yau-3 categories with a simple combinatorial presentation through the study of the period map of meromorphic differentials on associated families of elliptic curves.

### 19.07.2016 13:00 Tim Kirschner: Finite quotients of three-dimensional complex tori

I will report on a current project with Patrick Graf (Bayreuth). Using Graf's recent results about the algebraic approximation of Kähler threefolds of Kodaira dimension zero, we show that a three-dimensional compact, connected Kähler space *X* with isolated canonical singularities is the finite quotient of a complex torus if and only if the first and second Chern classes of *X* vanish. This brings together an old theorem of Yau (where *X* is smooth) and a theorem of Shepherd-Barron and Wilson (where *X* is projective).

### 14.07.2016 14:00 James Pascaleff: Symplectic Cohomology and Wall Crossing

In this talk I will describe a way that certain wall-crossing formulae can be seen in terms of symplectic cohomology, which is a Floer theoretic invariant of non-compact symplectic manifolds. In the case of log Calabi-Yau manifolds, this invariant is supposed to be mirror-dual to the poly-vector fields. I will draw connections to the theory of cluster varieties as studied by Gross-Hacking-Keel-Kontsevich. This is partially based on discussions with Dmitry Tonkonog (Cambridge).

### 26.04.2016 13:00 Mohammad Akhtar: Mirror symmetry and the classification of Fano varieties

The classification of Fano varieties is an important long-standing problem in algebraic geometry. A new approach to this problem via mirror symmetry was recently proposed by Coates-Corti-Galkin-Golyshev-Kasprzyk. Their philosophy was that Fano varieties can be classified by studying their Laurent polynomial mirrors. This talk will survey the results of a collaborative effort to apply this philosophy to the classification of Fano orbifold surfaces. We will describe a conjectural picture which suggests that classifying suitable deformation classes of certain Fano orbifold surfaces is equivalent to classifying Fano lattice polygons up to an appropriate notion of equivalence. Central to this framework is the notion of mirror duality (between a Fano orbifold surface and a Laurent polynomial) and the closely related operations of algebraic and combinatorial mutations. We will also discuss how combinatorial mutations allow us to find mirror dual Laurent polynomials in practice and will give experimental evidence supporting our conjectures.

### 07.01.2016 12:00 Andreas Gross: Intersection Theory on Tropicalizations of h3 Embeddings

A central goal of tropical geometry is to give combinatoric descriptions of algebro-geometric objects. In enumerative geometry, these description ideally give rise to so-called correspondence theorems, which state that some given algebraic enumerative problem can be translated into a tropical enumerative problem with the same solution. The tropical intersection theory of Allermann and Rau has become a useful tool in tropical enumerative geometry, its connection to algebraic geometry being based on the description of the intersection ring of complete toric varieties by Fulton and Sturmfels. Unfortunately, moduli spaces are rarely toric, yet in many cases they are toroidal.

In my talk I will outline how to extend the scope of tropical intersection theory to be able to describe certain intersections on toroidal varieties.

### 17.12.2015 12:00 Sara Filippini: Refined curve counting and the tropical vertex group

The tropical vertex group of Kontsevich and Soibelman is generated by formal symplectomorphisms of the 2-dimensional algebraic torus. It plays a role in many problems in algebraic geometry and mathematical physics. Based on the tropical vertex group, Gross, Pandharipande and Siebert introduced an interesting Gromov-Witten theory on weighted projective planes which admits a very special expansion in terms of tropical counts.

I will describe a refinement or "q-deformation" of this expansion, motivated by wall-crossing ideas, using Block-Goettsche invariants. This leads naturally to the definition of a class of putative q-deformed curve counts. We prove that this coincides with another natural q-deformation, provided by a result of Reineke and Weist in the context of quiver representations, when the latter is well defined. This is joint work with Jacopo Stoppa.

### 29.10.2015 12:00 Aleksey Zinger: Normal Crossings Divisors for Symplectic Topology

I will describe purely symplectic notions of normal crossings divisor and configuration. They are compatible with the existence of the desired auxiliary almost Kahler structures, provided ``existence" is suitably interpreted. These notions lead to a multifold version of Gompf's symplectic sum construction. They also imply that Brett Parker's work on exploded manifolds concerns a multifold version of the usual symplectic sum (or degeneration) formula for Gromov-Witten invariants. We hope our approach can be extended to more general singularities and provide purely symplectic analogues of the singularities and their deformations appearing in the Gross-Siebert program. This is joint work with Mark McLean and Mohammad Tehrani.

### 25.06.2015 Peter Overholser: Descendent tropical mirror symmetry for P2

The Gross-Siebert program can be seen as an attempt to understand mirror symmetry from a tropical perspective. Gross has realized this goal in a particular example, giving a tropical description of mirror symmetry for P2. I will show how his construction can be modified to to yield a novel mirror symmetric relationship.