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Autumn Semester 2025

Date / Time Speaker Title Location
22 August 2025
15:00-16:30 		Dr. Nitin Chidambaram
University of Edinburgh
Details

Algebraic Geometry and Moduli Seminar

Title Theta classes: integrability, W-constraints and topological recursion
Speaker, Affiliation Dr. Nitin Chidambaram, University of Edinburgh
Date, Time 22 August 2025, 15:00-16:30
Location HG G 43
Abstract I will talk about a sequence of cohomology classes Theta^{r,s}_{g,n} on the moduli space of curves, which depend on two parameters (r,s) where 1 ≤ s ≤ r–1. Defined using the moduli space of r-th roots, Theta^{r,s} defines a non semi-simple CohFT of rank r–1 that can be viewed as an analogue of the Witten r-spin class (which corresponds to the case s = r+1). Theta^{r,s} satisfies various nice properties — the descendant potential is a tau function of the r-KdV hierarchy (i.e., a version of the Witten r-spin conjecture), satisfies W-algebra constraints, can be calculated via “determinantal formulas” and satisfies a generalised Eynard–Orantin style topological recursion.
Theta classes: integrability, W-constraints and topological recursionread_more
HG G 43
22 August 2025
16:45-18:00 		Prof. Dr. Rahul Pandharipande
Details

Algebraic Geometry and Moduli Seminar

Title R-matrix of the Hilbert scheme
Speaker, Affiliation Prof. Dr. Rahul Pandharipande,
Date, Time 22 August 2025, 16:45-18:00
Location HG G 43
R-matrix of the Hilbert scheme
HG G 43
24 September 2025
13:30-15:00 		Dr. Alessio Cela
Cambridge University
Details

Algebraic Geometry and Moduli Seminar

Title Pseudo-holomorphic curves with a fixed complex structure in positive symplectic manifolds
Speaker, Affiliation Dr. Alessio Cela, Cambridge University
Date, Time 24 September 2025, 13:30-15:00
Location HG G 43
Abstract In this talk, I will show that fixed-domain Gromov–Witten invariants of a positive symplectic manifold (e.g., a smooth Fano variety) are signed counts of J-holomorphic curves in X satisfying prescribed incidence conditions. This provides a symplectic analogue of a conjecture of Lian and Pandharipande, recently disproved in the algebraic setting by Beheshti, Lehmann, Lian, Riedl, Starr, and Tanimoto. The proof relies on constructing the fixed-domain Gromov–Witten pseudocycle without the use of inhomogeneous or domain-dependent perturbations, answering an old question posed by Ruan and Tian.
Pseudo-holomorphic curves with a fixed complex structure in positive symplectic manifoldsread_more
HG G 43
26 September 2025
16:00-17:30 		Dr. Calla Tschanz
Ruhr Universität Bochum
Details

Algebraic Geometry and Moduli Seminar

Title From logarithmic Hilbert schemes to degenerations of hyperkähler varieties
Speaker, Affiliation Dr. Calla Tschanz, Ruhr Universität Bochum
Date, Time 26 September 2025, 16:00-17:30
Location HG G 43
Abstract In this talk, I will discuss my previous work on constructing explicit models of logarithmic Hilbert schemes. This relates to work or Li-Wu on expanded degenerations, Gulbrandsen-Halle-Hulek on degenerations of Hilbert schemes of points and Maulik-Ranganathan on logarithmic Hilbert schemes. The constructions I consider are local. I will then explain how we globalise these in joint work with Shafi and apply them to construct minimal type III degenerations of hyperkähler varieties, namely Hilbert schemes of points on K3 surfaces.
From logarithmic Hilbert schemes to degenerations of hyperkähler varietiesread_more
HG G 43
3 October 2025
16:00-17:30 		Aitor Iribar López
ETH Zürich
Details

Algebraic Geometry and Moduli Seminar

Title A Theorem of Fritz Carlson
Speaker, Affiliation Aitor Iribar López, ETH Zürich
Date, Time 3 October 2025, 16:00-17:30
Location HG G 43
A Theorem of Fritz Carlson
HG G 43
8 October 2025
13:30-15:00 		Dr. Hyeonjun Park
Korea Institute for Advanced Study
Details

Algebraic Geometry and Moduli Seminar

Title Symplectic pushforwards and 3CY CoHA
Speaker, Affiliation Dr. Hyeonjun Park, Korea Institute for Advanced Study
Date, Time 8 October 2025, 13:30-15:00
Location HG G 43
Abstract In this talk, I will introduce a general operation of producing shifted symplectic stacks from given ones. Basic examples like cotangent bundles, critical loci, and Hamiltonian reduction can be understood as special cases of this operation. Moreover, this unification enables us to provide an etale local structure theorem for shifted symplectic Artin stacks. As an application, I will explain how to construct cohomological Hall algebras for 3-Calabi-Yau categories, which is joint work with Tasuki Kinjo and Pavel Safronov.
Symplectic pushforwards and 3CY CoHAread_more
HG G 43
10 October 2025
16:00-17:30 		Dr. Yannik Schüler-Hammer
ETH Zürich
Details

Algebraic Geometry and Moduli Seminar

Title Quintuple Hodge integrals
Speaker, Affiliation Dr. Yannik Schüler-Hammer, ETH Zürich
Date, Time 10 October 2025, 16:00-17:30
Location HG G 43
Abstract I will discuss recent progress on conjectural formulas for quintuple Hodge integrals. A proof of these formulas will be presented in two distinct limits, and I will discuss the obstructions to extending the arguments beyond the two regimes. I will also mention their implications for Gromov–Witten theory of toric Calabi–Yau fivefolds and string theory, with particular attention to constant map contributions.
Quintuple Hodge integralsread_more
HG G 43
17 October 2025
16:00-17:30 		Dr. Hyeonjun Park
Korea Institute for Advanced Study
Details

Algebraic Geometry and Moduli Seminar

Title Lagrangian classes and GLSM CohFT
Speaker, Affiliation Dr. Hyeonjun Park, Korea Institute for Advanced Study
Date, Time 17 October 2025, 16:00-17:30
Location HG G 43
Abstract In this talk, I will explain the construction of Lagrangian classes for perverse sheaves in cohomological Donaldson-Thomas theory, whose existence was conjectured by Joyce. The two key ingredients are a relative version of the DT perverse sheaves and a hyperbolic version of the dimensional reduction theorem. As a special case, we recover Borisov-Joyce/Oh-Thomas virtual classes in DT4 theory. As an application, I will explain how to construct cohomological field theories for gauged linear sigma models. This is joint work in progress with Adeel Khan, Tasuki Kinjo, and Pavel Safronov.
Lagrangian classes and GLSM CohFTread_more
HG G 43
22 October 2025
13:30-15:00 		Dr. Sam Canning
ETH Zürich
Details

Algebraic Geometry and Moduli Seminar

Title Cohomology of the Satake compactification I
Speaker, Affiliation Dr. Sam Canning, ETH Zürich
Date, Time 22 October 2025, 13:30-15:00
Location HG G 43
Cohomology of the Satake compactification I
HG G 43
24 October 2025
16:00-17:30 		Dr. Donggun Lee
IBS Center for Complex Geometry (Daejeon)
Details

Algebraic Geometry and Moduli Seminar

Title Representations on the cohomology of the moduli space of pointed rational curves
Speaker, Affiliation Dr. Donggun Lee, IBS Center for Complex Geometry (Daejeon)
Date, Time 24 October 2025, 16:00-17:30
Location HG G 43
Abstract The moduli space of pointed rational curves carries a natural action of the symmetric group permuting the marked points. In this talk, I will present combinatorial and recursive formulas for the induced representations on its cohomology. These formulas are obtained by relating the representation to that of the moduli space with one additional marked point fixed under the symmetric group action, which has a particularly nice and tractable structure. Taking the invariant subspace, in particular, leads to an effective inductive formula for the Betti numbers of the moduli space of rational curves with unordered markings. I will also discuss several interesting conjectural properties of these representations. This talk is based on joint work with Jinwon Choi and Young-Hoon Kiem.
Representations on the cohomology of the moduli space of pointed rational curvesread_more
HG G 43
29 October 2025
13:30-15:00 		Aitor Iribar López
ETH Zürich
Details

Algebraic Geometry and Moduli Seminar

Title Cohomology of the Satake compactification II
Speaker, Affiliation Aitor Iribar López, ETH Zürich
Date, Time 29 October 2025, 13:30-15:00
Location HG G 43
Cohomology of the Satake compactification II
HG G 43
31 October 2025
16:00-17:30 		Dr. Weite Pi
MPI Bonn
Details

Algebraic Geometry and Moduli Seminar

Title Perverse = Chern and χ-independence phenomena for moduli of 1-dimensional sheaves
Speaker, Affiliation Dr. Weite Pi, MPI Bonn
Date, Time 31 October 2025, 16:00-17:30
Location HG G 43
Abstract The goal of this talk is to discuss the geometry and intersection theory of Le Potier’s moduli space of 1-dimensional sheaves on the projective plane. We focus on two aspects: first, the "P=C" conjecture relating two filtrations of highly different nature on cohomology, which can be viewed as a del Pezzo analog of the celebrated P=W conjecture; second, the so-called χ-independence phenomenon, which stems from enumerative geometry and predicts surprising consequences on the cohomology of the moduli space. After surveying known results, I will explain how these two aspects are linked via an “associated graded” χ-independence conjecture (work in progress). This talk is primarily based on joint work with Yakov Kononov, Woonam Lim, and Miguel Moreira.
Perverse = Chern and χ-independence phenomena for moduli of 1-dimensional sheavesread_more
HG G 43
5 November 2025
13:30-15:00 		Jeremy Feusi
ETH Zürich
Details

Algebraic Geometry and Moduli Seminar

Title Cohomology of the Satake compactification III
Speaker, Affiliation Jeremy Feusi, ETH Zürich
Date, Time 5 November 2025, 13:30-15:00
Location HG G 43
Cohomology of the Satake compactification III
HG G 43
7 November 2025
16:00-17:30 		Dr. Sam Canning
ETH Zürich
Details

Algebraic Geometry and Moduli Seminar

Title Tree contributions
Speaker, Affiliation Dr. Sam Canning, ETH Zürich
Date, Time 7 November 2025, 16:00-17:30
Location HG G 43
Abstract I will talk about how to compute the contributions from each strata in the fiber product for the Torelli pullback of the product loci calculations. I will explain some examples, the algorithm in general, and then we can have a discussion about implementation strategies.
Tree contributionsread_more
HG G 43
12 November 2025
13:30-15:00 		Aitor Iribar López
ETH Zürich
Details

Algebraic Geometry and Moduli Seminar

Title Cohomology of the Satake compactification IV
Speaker, Affiliation Aitor Iribar López, ETH Zürich
Date, Time 12 November 2025, 13:30-15:00
Location HG G 43
Cohomology of the Satake compactification IV
HG G 43
14 November 2025
16:00-17:00 		Dr. Max Schimpf
MPI Bonn
Details

Algebraic Geometry and Moduli Seminar

Title Grothendieck topologies with log modifications
Speaker, Affiliation Dr. Max Schimpf, MPI Bonn
Date, Time 14 November 2025, 16:00-17:00
Location HG G 43
Abstract Many notions in log geometry are invariant under log modification. To formalize this, we introduce the so-called m-type morphisms and their associated topologies and discuss their properties. In particular, this lead us to discover a mistake in the definition of the full log étale site introduced by Kazuya Kato and Fujiwara 30 years ago. Moreover, I will also present a fix for this problem. Time permitting, I will talk about applications of our topologies. All the above results are joint with Xianyu Hu.
Grothendieck topologies with log modificationsread_more
HG G 43
14 November 2025
17:15-18:15 		Sofia Wood
Columbia University
Details

Algebraic Geometry and Moduli Seminar

Title Hodge numbers of universal compactified Jacobians
Speaker, Affiliation Sofia Wood, Columbia University
Date, Time 14 November 2025, 17:15-18:15
Location HG G 43
Abstract We study the universal compactified Jacobians of degree d, as constructed by Kass and Pagani over the moduli space of stable curves. These spaces compactify the universal degree-d Jacobian over the moduli of smooth curves, and depend on a choice of universal stability condition. I will discuss the proof of how the Hodge numbers of these compactified Jacobians are independent of both the degree d and the choice of stability condition. This is joint work with Rahul Pandharipande, Dan Petersen, and Johannes Schmitt.
Hodge numbers of universal compactified Jacobiansread_more
HG G 43
21 November 2025
16:00-17:30 		Prof. Dr. Georg Oberdieck
Universität Heidelberg
Details

Algebraic Geometry and Moduli Seminar

Title On the multiple cover formulas for K3 and abelian surfaces
Speaker, Affiliation Prof. Dr. Georg Oberdieck, Universität Heidelberg
Date, Time 21 November 2025, 16:00-17:30
Location HG G 43
Abstract It has been conjectured that the Gromov-Witten invariants of a K3 or abelian surface for arbitrary curve classes are determined by those for primitive curve classes by a very simple multiple cover rule. The primitive invariants in turn are known, so the conjecture would determine the entire Gromov-Witten theory of K3 and abelian surfaces. In this talk I will report on joint work in progress with Rahul Pandharipande in which we aim to prove this conjecture.
On the multiple cover formulas for K3 and abelian surfacesread_more
HG G 43
28 November 2025
16:00-17:30 		Dr. Alessandro Giacchetto
ETH Zürich
Details

Algebraic Geometry and Moduli Seminar

Title Refining Witten–Kontsevich
Speaker, Affiliation Dr. Alessandro Giacchetto, ETH Zürich
Date, Time 28 November 2025, 16:00-17:30
Location HG G 43
Abstract The combinatorial description of the moduli space of curves in terms of ribbon graphs was one of the crucial ingredients in Kontsevich’s proof of Witten’s conjecture. The same model was used by Harer–Zagier and by Norbury to compute the Euler characteristic and the number of lattice points, respectively. In this talk, we will introduce the analogous combinatorial model for the moduli space of real curves: the moduli of metric Möbius graphs. Each such graph is equipped with a measure of non-orientability, a quantity interpolating between the complex and the real worlds. We then provide recursive formulas for the volumes and the lattice point counts of this moduli space, refining the results of Kontsevich and Norbury. Finally, we compute the refined Euler characteristic, thereby answering a question posed by Goulden, Harer, and Jackson 25 years ago.
Refining Witten–Kontsevichread_more
HG G 43
3 December 2025
13:30-15:00 		Prof. Dr. Dan Petersen
Stockholm University
Details

Algebraic Geometry and Moduli Seminar

Title Moments in families of L-functions over function fields via homological stability of moduli spaces
Speaker, Affiliation Prof. Dr. Dan Petersen, Stockholm University
Date, Time 3 December 2025, 13:30-15:00
Location HG G 43
Abstract This is a report of joint work with Bergström-Diaconu-Westerland and Miller-Patzt-Randal-Williams. There is a "recipe" due to Conrey-Farmer-Keating-Rubinstein-Snaith which allows for precise predictions for the asymptotics of moments of many different families of L-functions. Our work concerns the CFKRS predictions in the case of the quadratic family over function fields, i.e. the family of all L-functions attached to hyperelliptic curves over some fixed finite field. One can relate this problem to understanding the homology of the moduli space of hyperelliptic curves with symplectic coefficients. With Bergström-Diaconu-Westerland we compute the stable homology groups of the moduli space of hyperelliptic curves with these coefficients, together with their structure as Galois representations. We moreover show that the answer matches the number-theoretic predictions. With Miller-Patzt-Randal-Williams we prove a uniform range for homological stability with these coefficients. Together, these results imply the CFKRS predictions for all moments in the function field case, for all sufficiently large (but fixed) q.
Moments in families of L-functions over function fields via homological stability of moduli spacesread_more
HG G 43
5 December 2025
16:00-17:30 		Dr. Denis Nesterov
ETH Zürich
Details

Algebraic Geometry and Moduli Seminar

Title Unramified maps to abelian varieties
Speaker, Affiliation Dr. Denis Nesterov, ETH Zürich
Date, Time 5 December 2025, 16:00-17:30
Location HG G 43
Abstract Spaces of unramified maps are a higher-dimensional generalization of spaces of admissible covers, introduced by Kim, Kresch, and Oh. I will discuss unramified maps to abelian varieties and how they can be used to compute cycles associated with spaces of stable maps. Joint work with Jeremy Feusi and Aitor Iribar López.
Unramified maps to abelian varietiesread_more
HG G 43
10 December 2025
13:30-15:00 		Dr. Olivier de Gaay Fortman
University of Utrecht
Details

Algebraic Geometry and Moduli Seminar

Title Matroids, the integral Hodge conjecture for abelian varieties, and optimal algebraic multiples of the minimal class
Speaker, Affiliation Dr. Olivier de Gaay Fortman, University of Utrecht
Date, Time 10 December 2025, 13:30-15:00
Location HG G 43
Abstract I will discuss joint work with Philip Engel and Stefan Schreieder, in which we prove that the cohomology class of any curve on a very general principally polarized abelian variety of dimension at least 4 is an even multiple of the minimal class, and that the same holds for the intermediate Jacobian of a very general cubic threefold. This disproves the integral Hodge conjecture for abelian varieties and shows that very general cubic threefolds are not stably rational. I will also discuss our most recent result, which shows that on a very general principally polarized abelian 6-fold, the smallest multiple of the minimal curve class which can be represented by an algebraic cycle is exactly 6.
Matroids, the integral Hodge conjecture for abelian varieties, and optimal algebraic multiples of the minimal classread_more
HG G 43
12 December 2025
16:00-17:30 		Daniel Holmes
IST Austria
Details

Algebraic Geometry and Moduli Seminar

Title Interactions between Gromov-Witten theory and GKM theory
Speaker, Affiliation Daniel Holmes, IST Austria
Date, Time 12 December 2025, 16:00-17:30
Location HG G 43
Abstract GKM spaces are important examples in algebraic and symplectic geometry, including smooth toric varieties, homogeneous spaces, smooth Schubert varieties, and non-algebraic examples like the twisted flag manifold. I will quickly introduce the main concepts of GKM theory and explain how the GKM graph completely determines the Gromov-Witten invariants and hence quantum cohomology of its space. This opens up a two-way interaction between the two theories: while GKM theory provides computability, GW theory provides necessary conditions for the Hamiltonian GKM realization problem. I will sketch some first results in both directions and introduce our new software package "GKMtools", which supports explicit computations at this intersection. Joint work with Giosuè Muratore.
Interactions between Gromov-Witten theory and GKM theoryread_more
HG G 43
17 December 2025
13:30-15:00 		Lycka Drakengren
ETH Zürich
Details

Algebraic Geometry and Moduli Seminar

Title Title T.B.A.
Speaker, Affiliation Lycka Drakengren, ETH Zürich
Date, Time 17 December 2025, 13:30-15:00
Location HG G 43
Title T.B.A.
HG G 43
16 January 2026
16:00-17:00 		Dr. Francesca Carocci
Roma Tor Vergata
Details

Algebraic Geometry and Moduli Seminar

Title Title T.B.A.
Speaker, Affiliation Dr. Francesca Carocci, Roma Tor Vergata
Date, Time 16 January 2026, 16:00-17:00
Location HG G 43
Title T.B.A.
HG G 43
16 January 2026
17:15-18:15 		Dr. Thomas Blomme
Universite de Neuchatel
Details

Algebraic Geometry and Moduli Seminar

Title Title T.B.A.
Speaker, Affiliation Dr. Thomas Blomme, Universite de Neuchatel
Date, Time 16 January 2026, 17:15-18:15
Location HG G 43
Title T.B.A.
HG G 43

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