# Algebraic Geometry

Organizer: Ravi Vakil

## Past Events

In my talk, I will start by reviewing how various properties of characteristic zero singularities can be understood topologically by ways of the Riemann-Hilbert correspondence. After that, I will explain how similar ideas can be applied in the study of mixed characteristic singularities.…

The moduli spaces of one-dimensional sheaves on the projective plane have been studied through their connections to enumerative geometry and representation theory. In this talk, I will explain a systematic approach to study their cohomology rings, using notably tautological relations of…

We give a new proof, along with some generalizations, of a folklore theorem - attributed to Laurent Lafforgue - that a rigid matroid (i.e., a matroid whose base polytope is indecomposable) has only finitely many projective equivalence classes of representations over any given field. A key…

I will talk about a new algebra of operations on polynomials which has the property

$T_iT_j=T_jT_{i+1}$ for $i>j$ and a family of polynomials dual to them called forest polynomials. This family of operations plays the exact role for quasisymmetric polynomials and forest polynomials as…

We survey some extensions of the classical notions of Du Bois and rational singularities, known as the k-Du Bois and k-rational singularities. By now, these notions are well-understood for local complete intersections (lci). We explain the difficulties beyond the lci case, and propose new…

Given a nondegenerate smooth variety X in P^n, let S(X) (resp. T(X)) be the subvariety of the Grassmannian Gr(2, n+1) consisting of secant (resp. tangent) lines to X. I will give closed-form formulae for the classes of S(X) and T(X) in the Chow ring of Gr(2,n+1) in terms of the “higher…

Given a nondegenerate smooth variety X in P^n, let S(X) (resp. T(X)) be the subvariety of the Grassmannian Gr(2, n+1) consisting of secant (resp. tangent) lines to X. I will give closed-form formulae for the classes of S(X) and T(X) in the Chow ring of Gr(2,n+1) in terms of the “higher…

The classical question of determining which varieties are rational has led to a huge amount of interest and activity. On the other hand, one can consider a complementary perspective - given a smooth projective variety whose nonrationality is known, how "irrational" is it? I will survey…

I will describe some connections between arithmetic geometry of abelian varieties, non-archimedean/tropical geometry, and combinatorics. For a principally polarized abelian variety, we show an identity relating the Faltings height and the Néron--Tate height (of a symmetric effective divisor…

Given a compact Riemann surface, nonabelian Hodge theory relates topological and algebro-geometric objects associated to it. Specifically, complex representations of the fundamental group are in correspondence with algebraic vector bundles, equipped with an extra structure called a Higgs field.…