Webinars

In 2020 the VBAC group launched a series of Webinars due to the pandemic situation. Due to the success of the series it was decided to continue it with 4-5 webinars each academic year, starting in late September.

The first VBAC webinar was A tribute to C. S. Seshadri organised in September 2020. Information on previous webinars can be found here.

Upcoming VBAC Webinars

All times are in UTC (GMT). Advance registration is required; follow this link to register.

(Click on the title of the talks for abstracts.)

The upcoming webinars in the 2024-25 academic year are planned for September, November, January, March and May.

Special subvarieties of the moduli space of abelian varieties — 16 September 2024

(Click on the title of the talks for abstract and video.)

14:00 - 14:45 Paola Frediani (Università di Pavia) : Asymptotic directions in the moduli space of curves

Abstract: I will report on a joint work with E. Colombo and G.P. Pirola, where we study asymptotic directions in the tangent bundle of the moduli space of curves of genus g, namely those tangent directions that are annihilated by the second fundamental form of the Torelli map. I will give examples of asymptotic directions for any g at least 4. I will show that if the rank d of a tangent direction at [C] (with respect to the infinitesimal deformation map) is less than the Clifford index of the curve C, then the tangent direction is not asymptotic. If the rank of a tangent direction v is equal to the Clifford index of the curve, I will give sufficient conditions ensuring that the infinitesimal deformation v is not asymptotic. Finally I will determine all asymptotic directions of rank 1 and give an almost complete description of asymptotic directions of rank 2.

15:00 - 15:45 Olivier de Gaay Fortman (University of Utrecht): Powers of an abelian variety isogenous to a Jacobian

Abstract: The Coleman—Oort conjecture concerns positive dimensional special subvarieties in the moduli space A_g of principally polarized abelian varieties of dimension g over the complex numbers. It predicts that the generic point of such a subvariety is not contained in the Torelli locus, provided that g is sufficiently large. I will prove this conjecture for those special subvarieties of A_g for which the generic abelian variety is isogenous to a power of a lower-dimensional abelian variety. More precisely: for a very general ppav of dimension at least four, no power is isogenous to a product of Jacobians of smooth projective curves. This is joint work with Stefan Schreieder.