On March 24, 2023, the next meeting of the BelgianDutch Algebraic Geometry seminar will be held at Radboud University Nijmegen. Location: room HG00.303 (ground floor) in the Huygens Building, Heyendaalseweg 135, Nijmegen.
Note: participation is free (including an informal dinner after the talks); but for practical reasons we ask that you register, no later than March 17, via this link. Thank you!
Programme (click a title to show/hide the abstract) 

13:1514:15  Alexander Petrov (Harvard and MPI Bonn)  Decomposability of the de Rham complex in positive characteristic
Abstract: Deligne and Illusie proved that if a smooth variety over F_{p} admits a lift over Z/p^{2} then the truncation of its de Rham complex in degrees < p is quasiisomorphic to the direct sum of its cohomology sheaves. As a consequence, the Hodgetode Rham spectral sequence of a smooth proper liftable variety degenerates, provided that the dimension of the variety is ≤ p.
It turns out that further truncations of the de Rham complex of a liftable variety need not be decomposable. I will describe the obstruction to decomposing the truncation of the de Rham complex in degrees ≤ p in terms of other invariants of the variety, and will use this to give an example of a smooth projective variety over F_{p} that lifts to Z_{p} but whose Hodgetode Rham spectral sequence does not degenerate at the first page. The proof proceeds by first understanding the obstruction to the formality of the de Rham complex as a commutative algebra (in the appropriate derived sense) using an analog of Steenrod operations from algebraic topology. 
14:4515:45  Sabrina Pauli (DuisburgEssen)  Counting curves over an arbitrary field using tropical geometry
Abstract: A tropical curve is a graph embedded in R^2 satisfying a number of conditions.
Mikhalkin's celebrated correspondence theorem establishes a correspondence between algebraic curves and tropical curves.
This translates the difficult question of counting plane rational curves of degree d through 3d1 points to the question of counting tropical curves with a given notion of multiplicity through 3d1 points which can be solved using combinatorics. There are two versions of this correspondence, one for the count of complex curves and one for the real count.
In the talk, I will present work in progress joint with Andrés Jaramillo Puentes in which we provide a version Mikhalkin's correspondence theorem over an arbitrary base field k.
I will also give a short introduction to counting curves over different fields and tropical geometry.

16:1517:15  Emanuele Macrì (Orsay)  HyperKähler manifolds and Lagrangian fibrations
Abstract: A hyperKähler manifold is a complex Kähler manifold that is simply connected, compact, and has a unique holomorphic symplectic form, up to constants. This important class of manifolds has been studied in the past in many contexts, from an arithmetic, algebraic, geometric point of view, and in applications to physics and dynamics. The theory in dimension two, namely K3 surfaces, is well understood.
The aim of the seminar is to give an introduction to the theory of hyperKähler manifolds in higher dimension, from a point of view of their classification; in particular, about existence of Lagrangian fibrations.
We will present some results in dimension four, obtained recently in collaboration with Olivier Debarre, Daniel Huybrechts and Claire Voisin.

December 9, 2022, at the University of Amsterdam 

Piotr Achinger (IMPAN)  The RiemannHilbert correspondence for rigid spaces  
Laura Pertusi (Milan)  Moduli spaces of stable objects in Enriques categories  
Dustin Clausen (Copenhagen)  Algebraic geometry from the solid perspective  
September 30, 2022, at the KU Leuven 

Javier de Bobadilla (BCAM)  Monodromy at radius zero and equimultiplicity of families with constant Milnor number  
Valentijn Karemaker (Utrecht)  The Gauss problem for central leaves  
Gebhard Martin (Bonn)  On the nondegeneracy of Enriques surfaces  
November 8, 2019, at the University of Antwerp 

Lie Fu (Lyon and Nijmegen)  Orbifold products on motivic cohomology and hyperKaehler resolution conjectures  
Špela Špenko (UL Bruxelles)  Perverse schobers in geometric invariant theory  
Stefan Kebekus (Freiburg)  Extension Theorems for differential forms and applications  
June 21, 2019, at the University of Amsterdam 

Diletta Martinelli (Edinburgh)  On the geometry of contractions of the Moduli Space of sheaves of a K3 surface  
Zsolt Patakfalvi (EPFL)  On the BeauvilleBogomolov decomposition in positive characteristic  
Yichao Tian (Strasbourg)  Geometry of unitary Shimura varieties at nonquasisplit primes and arithmetic applications  
February 1, 2019, at Utrecht University 

Dan Petersen (Stockholm University)  Tautological classes with twisted coefficients  
Donatella Iacono (Università di Bari)  DGLie algebras and deformation of pairs  
Georg Oberdieck (University of Bonn)  Quantum cohomology of the Hilbert scheme of pairs  
September 20 and 21, 2018 at Radboud University Nijmegen 

ChingLi Chai (UPenn)  Sustained pdivisible groups and the foliation on moduli spaces of abelian varieties  
Jörg Wildeshaus (Paris 13)  Weights and conservativity  
Kestutis Cesnavicius (CNRS/ParisSud)  Purity for the Brauer group  
Claire Voisin (Collège de France)  Gonality and zerocycles of abelian varieties  
Victoria Hoskins (FU Berlin)  On the motive of the stack of vector bundles on a curve  
Richard Thomas (Imperial College)  Refined VafaWitten invariants for projective surfaces  
Piotr Achinger (IMPAN, Warsaw)  SerreTate theory for CalabiYau varieties  
June 8, 2018 at the KU Leuven 

Arend Bayer (Edinburgh)  Families of Hyperkaehler varieties via families of stability conditions  
Christian Liedtke (Technische Universität München)  A NéronOggShafarevich criterion for K3 Surfaces  
José Burgos Gil (ICMAT, Madrid)  Grothendieck's period conjecture and zeta values  
March 23, 2018 at Leiden University 

Videos of the lectures are available via youtube.  
Florian Ivorra (FRIAS, Freiburg)  Quasiunipotent motives  
Peter Jossen (ETH Zürich)  Galois groups and Motivic Fundamental groups  
Lionel Darondeau (KU Leuven)  Jet differentials and hyperbolicity  
December 15, 2017 at Radboud University Nijmegen 

Johannes Nicaise (Imperial College and Leuven)  Specialization of (stable) rationality in families with mild singularities  
Javier Fresán (École Polytechnique)  Exponential motives  
Michael Groechenig (FU Berlin)  padic integration for the Hitchin system  
December 9, 2016 at the University of Amsterdam 

June Huh (Princeton)  Enumeration of points, lines, planes, etc.  
Dieter Kotschick (München) and Stefan Schreieder (Bonn)  The Hodge ring of Kähler manifolds  
Bhargav Bhatt (Ann Arbor)  Derived splinters in mixed characteristic  
April 22, 2016 at KU Leuven 

Sho Tanimoto (Copenhagen)  Towards a refinement of Manin's conjecture  
John Christian Ottem (Oslo)  Effective cones of cycles on blowups of projective space  
Bruno Chiarellotto (Padova)  Monodromy action and special fiber for semistable schemes over a DVR  
December 11, 2015 at Leiden University 

David Holmes (Leiden)  Models of degenerating jacobians  
Clément Dupont (MPIM Bonn)  Motives of biarrangements  
Misha Verbitsky (ULB, Bruxelles)  Transcendental Hodge algebra  
June 11 and 12, 2015 in Nijmegen, joint with NoGAGS 

Daniel Greb (DuisburgEssen)  Movable curves and semistable sheaves  
Klaus Künnemann (Regensburg)  A tropical approach to nonarchimedean Arakelov geometry  
Kevin Buzzard (Imperial College)  Preadic spaces and adic spaces  
Tim Dokchitser (Bristol)  Local arithmetic of hyperelliptic curves  
David Rydh (KTH Stockholm)  The local structure of Artin stacks  
Lars Kindler (FU Berlin)  Ramification theory for Dmodules in positive characteristic  
Christian Lehn (Hannover)  Rational curves on singular cubic fourfolds  
Ulf Kühn (Hamburg)  A geometric approach to constructing elements of K_{2} of curves  
November 14, 2014 at the University of Amsterdam 

Minhyong Kim (Oxford)  Nonabelian reciprocity laws and Diophantine geometry  
Mingmin Shen (UvA)  Multiplicative ChowKünneth decompositions  
Jakob Stix (Frankfurt)  Gorenstein orders and abelian varieties over finite fields  
May 16, 2014 in Leuven 

Olivier Benoist (Strasbourg)  Complete families of smooth space curves  
FrankOlaf Schreyer (Saarbrücken)  Matrix factorizations and families of curves of genus 15  
Carel Faber (Utrecht)  On the cohomology of the moduli spaces of pointed curves of genus three  
November 22, 2013 in Nijmegen 

Nero Budur (Leuven)  Cohomology jump loci  
Stefan Schröer (Düsseldorf)  Wild quotient surface singularities  
René Schoof (Rome)  Finite group schemes and abelian varieties with good reduction outside one prime  
June 14, 2013 in Leiden 

Walter Gubler (Regensburg)  Normal toric varieties over valuation rings of rank 1  
Gaël Rémond (Bordeaux)  Isogenies and polarizations  
JeanBenoît Bost (Orsay)  Pluripotential theory, heights, and algebraization on arithmetic threefolds  
José Ignacio Burgos Gil (ICMAT Madrid)  The singularities of the invariant metric of the sheaf of Jacobi forms on the universal elliptic curve  
April 19, 2013 in Leuven 

Alejandro Soto (Regensburg)  Toric Varieties over a Valuation Ring  
Sébastien Boucksom (Jussieu)  A uniform version of Izumi's theorem  
Ariyan Javanpeykar (Leiden)  Bounds for Arakelov invariants  algorithmic and Diophantine applications  
December 7, 2012 at the UvA 

Andrei Caldararu (Wisconsin)  Derived intersections  
Eduard Looijenga (Utrecht)  Cohomological dimension of moduli spaces of curves  
Daniel Huybrechts (Bonn)  Cycles on K3 surfaces  
June 15, 2012 in Leuven 

Ted Chinburg (UPenn)  Small generators for Sarithmetic groups  
Matthieu Romagny (Jussieu)  Models of groups schemes of roots of unity  
Mircea Mustaţă (Michigan)  Adjoint line bundles in positive characteristic 