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Spring Semester 2015

Date / Time Speaker Title Location
* 18 February 2015
14:00-16:00 		Prof. Dr. Paul Biran
ETH Zurich, Switzerland
Details

Algebraic Geometry and Moduli Seminar

Title The Lagrangian cubic equation
Speaker, Affiliation Prof. Dr. Paul Biran, ETH Zurich, Switzerland
Date, Time 18 February 2015, 14:00-16:00
Location HG G 19.2
The Lagrangian cubic equation
HG G 19.2
* 20 February 2015
16:00-17:30 		E. Clader / F. Janda
ETH Zurich
Details

Algebraic Geometry and Moduli Seminar

Title Pixton's double ramification cycle relations
Speaker, Affiliation E. Clader / F. Janda , ETH Zurich
Date, Time 20 February 2015, 16:00-17:30
Location HG G 43
Abstract Pixton recently has proposed a formula for the double ramification (DR) cycle, which describes the class of the locus of curves admitting a map to the projective line with specified ramification conditions along 0 and infinity. His formula takes the form of an inhomogenous class which is conjectured to vanish above some degree and whose top degree part coincides with the DR-cycle. We discuss a proof of the vanishing and its relation to other relations in the cohomology of the moduli space of curves.
Pixton's double ramification cycle relationsread_more
HG G 43
25 February 2015
13:30-15:30 		Ran Tessler
Hebrew University of Jerusalem
Details

Algebraic Geometry and Moduli Seminar

Title The combinatorial formula for descendent integrals on the moduli space of open surfaces I
Speaker, Affiliation Ran Tessler, Hebrew University of Jerusalem
Date, Time 25 February 2015, 13:30-15:30
Location HG G 43
Abstract We shall recall the definition of open descendent integrals in genus 0 (a joint work with Rahul Pandharipande and Jake Solomon). Then, after collecting some facts from related branches of geometry and topology, we will find an effective formula for the descendent integrals in terms of weighted sums over graphs. If time permits we shall briefly define the high genus descendents (joint with Solomon), show how to modify the combinatorial formula for these cases.
The combinatorial formula for descendent integrals on the moduli space of open surfaces Iread_more
HG G 43
* 27 February 2015
16:00-17:15 		Ran Tessler
Hebrew University of Jerusalem
Details

Algebraic Geometry and Moduli Seminar

Title The combinatorial formula for descendent integrals on the moduli space of open surfaces II
Speaker, Affiliation Ran Tessler, Hebrew University of Jerusalem
Date, Time 27 February 2015, 16:00-17:15
Location HG G 43
Abstract We shall recall the definition of open descendent integrals in genus 0 (a joint work with Rahul Pandharipande and Jake Solomon). Then, after collecting some facts from related branches of geometry and topology, we will find an effective formula for the descendent integrals in terms of weighted sums over graphs. If time permits we shall briefly define the high genus descendents (joint with Solomon), show how to modify the combinatorial formula for these cases.
The combinatorial formula for descendent integrals on the moduli space of open surfaces IIread_more
HG G 43
4 March 2015
13:30-15:30 		Johannes Schmitt
ETH Zürich
Details

Algebraic Geometry and Moduli Seminar

Title A compactification of the moduli space of self maps of CP1
Speaker, Affiliation Johannes Schmitt, ETH Zürich
Date, Time 4 March 2015, 13:30-15:30
Location HG G 43
A compactification of the moduli space of self maps of CP1
HG G 43
18 March 2015
13:30-15:30 		Jérémy Guéré
Humboldt Universität Berlin
Details

Algebraic Geometry and Moduli Seminar

Title Some FJRW invariants in any genus without concavity
Speaker, Affiliation Jérémy Guéré, Humboldt Universität Berlin
Date, Time 18 March 2015, 13:30-15:30
Location HG G 43
Abstract In this talk, I will first explain how to compute FJRW invariants in genus zero for a large class of polynomials which do not satisfy the concavity hypothesis. This should be seen as the counterpart of Gromov--Witten theory for hypersurfaces, in cases where convexity fails. A complete algebraic description of the FJRW virtual class has been recently provided by Polishchuk and Vaintrob and is based on matrix factorizations. I will sketch how to re-write this definition using a new characteristic class in K-theory, leading to the expression of the virtual class and to a mirror symmetry statement. At last, I will describe how the same ideas compute some FJRW invariants in arbitrary genus.
Some FJRW invariants in any genus without concavityread_more
HG G 43
* 20 March 2015
16:00-17:15 		Dr. Dan Petersen
University of Copenhagen
Details

Algebraic Geometry and Moduli Seminar

Title Tautological rings in genus three
Speaker, Affiliation Dr. Dan Petersen, University of Copenhagen
Date, Time 20 March 2015, 16:00-17:15
Location HG G 43
Abstract The tautological rings of the spaces M_{g,n}^{rt} of n-pointed curves of genus g with rational tails are so far only understood for (g,n) small enough. I will report on ongoing joint work with Mehdi Tavakol, where we have obtained rather precise results when g=3 and n is arbitrary: we have a complete set of generators for the ideal of tautological relations, we can show that the tautological ring is Gorenstein, and we can identify the tautological ring with the part of the cohomology ring which "comes from" the trivial local system and the local system V_{111}.
Tautological rings in genus threeread_more
HG G 43
25 March 2015
13:30-15:30 		Prof. Dr. Nicolas Bergeron
Université Pierre et Marie Curie, Paris
Details

Algebraic Geometry and Moduli Seminar

Title Arithmetic manifolds and their cohomology (a biased overview)
Speaker, Affiliation Prof. Dr. Nicolas Bergeron, Université Pierre et Marie Curie, Paris
Date, Time 25 March 2015, 13:30-15:30
Location HG G 43
Abstract I will first give a quick introduction to arithmetic manifolds with emphasis on the one associated to orthogonal groups. I will then address the question of constructing classes in the cohomology of these manifolds. To do so we essentially have two basic methods at our disposal. The first, geometric, involves some special (totally geodesic) cycles, and the problem is to show that these contribute to the cohomology. The second -- via a formula of Matsushima that I will recall -- consists in studying if certain unitary representations, called "cohomological", do occur in the automorphic spectrum. I will describe these different methods and relate them.
Arithmetic manifolds and their cohomology (a biased overview)read_more
HG G 43
* 27 March 2015
16:00-17:15 		Nicolas Bergeron
Université Pierre et Marie Curie, Paris
Details

Algebraic Geometry and Moduli Seminar

Title Special cycles in some arithmetic manifolds and the proof of the Noether-Lefschetz conjecture
Speaker, Affiliation Nicolas Bergeron, Université Pierre et Marie Curie, Paris
Date, Time 27 March 2015, 16:00-17:15
Location HG G 19.2
Abstract I will first briefly recall that the coarse moduli space of quasi-polarized K3 surfaces of genus g is isomorphic to some arithmetic manifold (orbifold in fact) and interpret the NL-cycles as special cycles. I will then sketch a proof that these special cycles generate the whole cohomology. The proof makes use of the recent stabilization of the twisted trace formula as well as related results of Arthur.
Special cycles in some arithmetic manifolds and the proof of the Noether-Lefschetz conjectureread_more
HG G 19.2
1 April 2015
13:00-14:45
Details

Algebraic Geometry and Moduli Seminar

Title Title T.B.A.
Speaker, Affiliation
Date, Time 1 April 2015, 13:00-14:45
Location HG G 43
Title T.B.A.
HG G 43
15 April 2015
13:30-15:30 		Dr. Alessandro Sisto
ETH Zürich
Details

Algebraic Geometry and Moduli Seminar

Title Mapping Class Groups and Gromov-hyperbolicity I
Speaker, Affiliation Dr. Alessandro Sisto, ETH Zürich
Date, Time 15 April 2015, 13:30-15:30
Location HG G 43
Abstract The Mapping Class Group of a (real) surface is the group of its diffeomorphisms modulo the diffeomorphisms isotopic to the identity, and it is the "orbifold fundamental group" of its Moduli Space of hyperbolic metrics. The first part of the talk will mostly be dedicated to motivating the study of Mapping Class Groups. In the second part I will discuss pseudo-Anosov mapping classes, in various senses the most interesting elements of Mapping Class Groups, and then introduce the curve graph, a remarkably useful tool to study Mapping Class Groups. Pseudo-Anosovs are precisely the mapping classes acting on the curve graph with unbounded orbits.
Mapping Class Groups and Gromov-hyperbolicity Iread_more
HG G 43
* 17 April 2015
16:00-17:00 		Dr. Martijn Kool
Utrecht
Details

Algebraic Geometry and Moduli Seminar

Title Stable pair invariants and surfaces with holomorphic 2-form
Speaker, Affiliation Dr. Martijn Kool, Utrecht
Date, Time 17 April 2015, 16:00-17:00
Location HG G 43
Abstract Gromov-Witten invariants of an algebraic surface S with a smooth connected curve C in the canonical linear system are zero unless the curve class is a multiple d[C]. These invariants have been studied by Lee-Parker, Maulik-Pandharipande and others. They only depend on the the sign (-1)^\chi(\O_S) and the restriction map from cohomology of S to cohomology of C. For d=2, we give a product formula for higher descendent stable stable pair invariants of the 3-fold X=K_S. Using cosection localization, we find that only C^* fixed stable pairs which are thickened in the fibre direction (but not the surface direction) contribute. For arbitrary d, we calculate that part of the theory, which comes from thickenings in the fibre direction only. This is work in progress with R. P. Thomas.
Stable pair invariants and surfaces with holomorphic 2-formread_more
HG G 43
* 17 April 2015
17:15-18:15 		Dr. Thomas Hudson
POSTECH, Korea
Details

Algebraic Geometry and Moduli Seminar

Title Fundamental classes of full and symplectic flag bundles in algebraic cobordism
Speaker, Affiliation Dr. Thomas Hudson, POSTECH, Korea
Date, Time 17 April 2015, 17:15-18:15
Location HG G 43
Abstract One of the first problems one has to address in Schubert calculus is how to express the fundamental classes of Schubert varieties. In the case of the Chow ring of the flag bundles associated to the classical groups, the Schubert classes were first computed by Fulton via a family of desingularizations known as Bott-Samelson resolutions. Starting from these same geometric inputs, the question can be restated and studied in the more general framework of the oriented cohomology theories of Levine and Morel. The aim of this talk is to present the geometry behind Fulton's original proof and to explain which difficulties one encounters in adapting them to algebraic cobordism, the universal oriented cohomology theory.
Fundamental classes of full and symplectic flag bundles in algebraic cobordismread_more
HG G 43
* 20 April 2015
15:30-16:30 		Dr. Alessandro Sisto
ETH Zürich
Details

Algebraic Geometry and Moduli Seminar

Title Mapping Class Groups and Gromov-hyperbolicity II
Speaker, Affiliation Dr. Alessandro Sisto, ETH Zürich
Date, Time 20 April 2015, 15:30-16:30
Location HG F 33.1
Abstract In this talk I will introduce the notion of Gromov-hyperbolicity of a metric space and prove that curve graphs are Gromov-hyperbolic. I will then discuss some aspects of the theory of group actions on Gromov-hyperbolic spaces, including the construction of elements with "interesting dynamics" (pseudo-Anosovs in the case of Mapping Class Groups), free subgroups and time permitting construction of quotients.
Mapping Class Groups and Gromov-hyperbolicity IIread_more
HG F 33.1
29 April 2015
13:30-15:30 		Prof. Dr. Dragos Oprea
UC San Diego
Details

Algebraic Geometry and Moduli Seminar

Title The Chern character of the Verlinde bundle I
Speaker, Affiliation Prof. Dr. Dragos Oprea, UC San Diego
Date, Time 29 April 2015, 13:30-15:30
Location HG G 43
Abstract Generalized theta functions are sections of determinant line bundles over the moduli space of semistable bundles over a fixed smooth curve. The dimension of the space of generalized theta functions is given by the well-studied Verlinde numbers. As the curve varies in moduli, one obtains in this fashion the Verlinde vector bundles over the moduli space of smooth curves. The theory of conformal blocks can be used to extend the Verlinde bundles over the boundary of the moduli space. In these lectures, I will explain some of the ideas involved in the above constructions. In addition, I will explain a formula for the total Chern character of the Verlinde bundles in terms of tautological classes. This is based on joint work with Alina Marian, Rahul Pandharipande, Aaron Pixton and Dimitri Zvonkine.
The Chern character of the Verlinde bundle Iread_more
HG G 43
6 May 2015
13:30-15:30 		Prof. Dr. Dragos Oprea
UC San Diego
Details

Algebraic Geometry and Moduli Seminar

Title The Chern character of the Verlinde bundle II
Speaker, Affiliation Prof. Dr. Dragos Oprea, UC San Diego
Date, Time 6 May 2015, 13:30-15:30
Location HG G 43
Abstract Generalized theta functions are sections of determinant line bundles over the moduli space of semistable bundles over a fixed smooth curve. The dimension of the space of generalized theta functions is given by the well-studied Verlinde numbers. As the curve varies in moduli, one obtains in this fashion the Verlinde vector bundles over the moduli space of smooth curves. The theory of conformal blocks can be used to extend the Verlinde bundles over the boundary of the moduli space. In these lectures, I will explain some of the ideas involved in the above constructions. In addition, I will explain a formula for the total Chern character of the Verlinde bundles in terms of tautological classes. This is based on joint work with Alina Marian, Rahul Pandharipande, Aaron Pixton and Dimitri Zvonkine.
The Chern character of the Verlinde bundle IIread_more
HG G 43
* 8 May 2015
15:45-16:45 		Adrien Sauvaget
Université Paris-Jussieu
Details

Algebraic Geometry and Moduli Seminar

Title Locus of abelian differentials with multiple zeros
Speaker, Affiliation Adrien Sauvaget, Université Paris-Jussieu
Date, Time 8 May 2015, 15:45-16:45
Location HG G 43
Locus of abelian differentials with multiple zeros
HG G 43
13 May 2015
13:30-15:30 		Prof. Dr. Dragos Oprea
UC San Diego
Details

Algebraic Geometry and Moduli Seminar

Title The Chern character of the Verlinde bundle III
Speaker, Affiliation Prof. Dr. Dragos Oprea, UC San Diego
Date, Time 13 May 2015, 13:30-15:30
Location HG G 43
Abstract Generalized theta functions are sections of determinant line bundles over the moduli space of semistable bundles over a fixed smooth curve. The dimension of the space of generalized theta functions is given by the well-studied Verlinde numbers. As the curve varies in moduli, one obtains in this fashion the Verlinde vector bundles over the moduli space of smooth curves. The theory of conformal blocks can be used to extend the Verlinde bundles over the boundary of the moduli space. In these lectures, I will explain some of the ideas involved in the above constructions. In addition, I will explain a formula for the total Chern character of the Verlinde bundles in terms of tautological classes. This is based on joint work with Alina Marian, Rahul Pandharipande, Aaron Pixton and Dimitri Zvonkine.
The Chern character of the Verlinde bundle IIIread_more
HG G 43
15 May 2015
16:00-17:00 		Rahul Pandharipande
ETH Zürich
Details

Algebraic Geometry and Moduli Seminar

Title The moduli of holomorphic and meromorphic differentials
Speaker, Affiliation Rahul Pandharipande, ETH Zürich
Date, Time 15 May 2015, 16:00-17:00
Location HG G 43
Abstract I will sketch a proposal for a compact moduli space of holomorphic/meromorphic differentials.
The moduli of holomorphic and meromorphic differentialsread_more
HG G 43
27 May 2015
13:30-14:45 		Junliang Shen
ETH Zürich
Details

Algebraic Geometry and Moduli Seminar

Title Motivic classes of generalized Kummer schemes via relative power structures
Speaker, Affiliation Junliang Shen , ETH Zürich
Date, Time 27 May 2015, 13:30-14:45
Location HG G 43
Abstract We describe the motivic theory of the generalized Kummer construction. Our method is to use a power structure over the Grothendieck ring of varieties relative to an abelian variety. As applications, we prove Goettsche's conjecture for geometrically ruled surfaces, and Gulbrandsen's conjecture for Euler characteristics. Moreover, we compute degree 0 motivic Donaldson-Thomas invariants for abelian geometries. This is a joint work with A. Morrison.
Motivic classes of generalized Kummer schemes via relative power structuresread_more
HG G 43
* 10 June 2015
13:30-14:30 		Sven Prüfer
Augsberg
Details

Algebraic Geometry and Moduli Seminar

Title Hurwitz numbers and symplectic geometry of moduli spaces of maps
Speaker, Affiliation Sven Prüfer, Augsberg
Date, Time 10 June 2015, 13:30-14:30
Location HG G 43
Abstract In this talk I will describe how to extend some of Mirzakhani's ideas for calculating psi-class intersections via Weil--Petersson volumes of Deligne--Mumford spaces to Hurwitz numbers and ramification cycles. The main idea is to consider moduli spaces of coverings of bordered Riemann surfaces together with marked points on the boundary and then use symplectic reduction for suitable torus actions. This is still work in progress.
Hurwitz numbers and symplectic geometry of moduli spaces of mapsread_more
HG G 43
25 June 2015
13:30-14:45 		Dr. Nick Sheridan
Princeton Univ.
Details

Algebraic Geometry and Moduli Seminar

Title Counting curves using the Fukaya category I
Speaker, Affiliation Dr. Nick Sheridan, Princeton Univ.
Date, Time 25 June 2015, 13:30-14:45
Location HG G 43
Abstract In 1991, string theorists Candelas, de la Ossa, Green and Parkes made a startling prediction for the number of curves in each degree on a generic quintic threefold, in terms of periods of a holomorphic volume form on a `mirror manifold'. Givental and Lian, Liu and Yau gave a mathematical proof of this version of mirror symmetry for the quintic threefold (and many more examples) in 1996. In the meantime (1994), Kontsevich had introduced his `homological mirror symmetry' conjecture and stated that it would `unveil the mystery of mirror symmetry'. I will explain how to prove that the number of curves on the quintic threefold matches up with the periods of the mirror via homological mirror symmetry. I will also attempt to explain in what sense this is `less mysterious' than the previous proof. The first talk will introduce the two versions of mirror symmetry: Hodge-theoretic (closed-string) mirror symmetry, and homological (open-string) mirror symmetry.The second talk will explain how open-string mirror symmetry implies closed-string mirror symmetry, via the open-closed string map. This is based on joint work with Sheel Ganatra and Tim Perutz.
Counting curves using the Fukaya category Iread_more
HG G 43
2 July 2015
15:15-16:30 		Dr. Nick Sheridan
Princeton Univ.
Details

Algebraic Geometry and Moduli Seminar

Title Counting curves using the Fukaya category II
Speaker, Affiliation Dr. Nick Sheridan, Princeton Univ.
Date, Time 2 July 2015, 15:15-16:30
Location HG G 43
Abstract In 1991, string theorists Candelas, de la Ossa, Green and Parkes made a startling prediction for the number of curves in each degree on a generic quintic threefold, in terms of periods of a holomorphic volume form on a `mirror manifold'. Givental and Lian, Liu and Yau gave a mathematical proof of this version of mirror symmetry for the quintic threefold (and many more examples) in 1996. In the meantime (1994), Kontsevich had introduced his `homological mirror symmetry' conjecture and stated that it would `unveil the mystery of mirror symmetry'. I will explain how to prove that the number of curves on the quintic threefold matches up with the periods of the mirror via homological mirror symmetry. I will also attempt to explain in what sense this is `less mysterious' than the previous proof. The first talk will introduce the two versions of mirror symmetry: Hodge-theoretic (closed-string) mirror symmetry, and homological (open-string) mirror symmetry.The second talk will explain how open-string mirror symmetry implies closed-string mirror symmetry, via the open-closed string map. This is based on joint work with Sheel Ganatra and Tim Perutz.
Counting curves using the Fukaya category IIread_more
HG G 43

Notes: events marked with an asterisk (*) indicate that the time and/or location are different from the usual time and/or location.

Organisers: Rahul Pandharipande

Archive: AS 24 SS 24 AS 23 SS 23 AS 22 SS 22 AS 21 SS 21 AS 20 SS 20 AS 19 SS 19 AS 18 SS 18 AS 17 SS 17 AS 16 SS 16 AS 15 SS 15 AS 14 SS 14 AS 13 SS 13 AS 12 SS 12 AS 11

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