| Enrico Arbarello (Rome) | Gerard van der Geer (Amsterdam) | |
| Daniel Huybrechts (Bonn) | Joshua Lam (HU Berlin) | |
| Rahul Pandharipande (ETH Zürich) | Stefan Schreieder (Hannover) | |
| Domenico Valloni (Hannover) | Claire Voisin (Paris) |
| Gavril Farkas | Bruno Klingler |
NoGAGS
The Northern German Algebraic Geometry Seminar is a regular joint seminar of the algebraic geometry groups in Berlin, Bielefeld, Hamburg, Hannover, Leipzig and Oldenburg. Information on the previous meetings can be found here.
Prize Winners
Two prizes will be awarded on this ocassion. They are:
Schedule
Abstractsclick to show or hideEnrico Arbarello Brill-Noether-Petri curves and K3 curves The talk describes results, by various authors, connected to the circle of ideas studied jointly with Edoardo Sernesi and Andrea Bruno in two articles, which appeared in “Algebraic Geometry" in 2014 and 2017.Gerard van der Geer Modular forms, moduli of curves and invariant theory We use effective divisors on projectivized Hodge bundles over moduli spaces of curves to construct modular forms. We show that invariant theory enables us to construct all vector valued Siegel modular forms of degree two and three from from such basic modular forms. This is joint work with Fabien Cléry, Carel Faber and Alexis Kouvidakis.Daniel Huybrechts The K3 category of a cubic fourfold — an update In this talk I will provide an update about what is known and what is not about the K3 category naturally associated with a smooth cubic fourfold.Joshua Lam Motivic local systems on curves By a local system on a complex curve, we mean simply a representation of its fundamental group. It is easy to write down examples of such, and in most cases they come in positive dimensional families. There are certain very special local systems, known as "motivic" or of "geometric origin", which have several favourable properties: these are the local systems which arise in the cohomologies of families of algebraic varieties. For example, such local systems have coefficients in a number field, and are isolated in moduli space. I will discuss some new results in this subject, such as examples where one can prove that motivic local systems are scarce using Hodge theory, as well as an example where one can construct infinitely many rank two local systems on a fixed curve. Some of this is joint work in progress with Daniel Litt.Rahul Pandharipande Cycles on the moduli space of abelian varieties I will present a new set of results and conjectures from the perspective of Noether-Lefschetz theory about cycles on the moduli space \(A_g\) of PPAVs. Joint work with S. Canning and D. Oprea.Stefan Schreieder A moving lemma for cohomology with support We prove a moving lemma for cohomology classes with support on smooth quasi-projective varieties with a smooth projective compactification. This generalizes the effacement theorem of Quillen, Bloch-Ogus, and Gabber. As an application we obtain a new proof of the Gersten conjecture in this case. In fact, our proof yields a stronger version of the Gersten conjecture, which answers in particular questions of Colliot-Thélène—Hoobler—Kahn. We will also discuss applications that go beyond the original framework of the Gersten conjecture.Domenico Valloni Reduction mod \(p\) of the Noether problem Let \(k\) be any field and let \(V\) be a linear and faithful representation of a finite group \(G\). The Noether problem asks whether \(V/G\) is a (stably) rational variety over k. It is known that if \(p = char(k) > 0\) and \(G\) is a \(p\)-group, then \(V/G\) is always rational. On the other hand, Saltman and later Bogomolov constructed many examples of \(p\)-groups \(G\) such that \(V/G\) is not stably rational over the complex numbers. In this talk we study what happens over dvr of mixed characteristic \((0,p)\). We show that for all the examples found by Saltaman and Bogomologov, there cannot exist a smooth projective scheme over \(R\) whose special and generic fibre are stably birational to \(V/G\). In particular, this proves that \(P^n_R/G\) never admits a relative resolution of singularities over \(R\). The proof combines integral \(p\)-adic Hodge theory with the study of indefinitely closed differential forms in positive characteristic.Claire Voisin Cycle classes on abelian varieties and the geometry of the Abel-Jacobi map We discuss two properties of an abelian variety, namely, being a direct summand in a product of Jacobians and the weaker property of being "split". We relate the first property to the integral Hodge conjecture for curve classes on abelian varieties. We also relate both properties to the existence problem for universal zero-cycles on Brauer-Severi varieties over abelian varieties. A similar relation is established for the existence problem of a universal codimension 2 cycle on a cubic threefold.Location
Buildings: Erwin Schrödinger-Zentrum and the Johann von Neumann-Haus (where the math institute locates). See the schedule above for the individual rooms. AcknowledgementThe event is generously supported by: 
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