3 papers
math.AG2026
Tautological modular forms of level two and degree two
Fabien Cléry, Gerard van der Geer
We show how to use divisors on the projectivized Hodge bundle to construct special vector-valued modular forms and then apply invariant theory to construct all vector-valued Siegel…
math.AG2024
On the number of real forms of a complex variety
Gerard van der Geer, Xun Yu
We give a bound on the number of weighted real forms of a complex variety with finite automorphism group, where the weight is the inverse of the number of automorphisms of the real…
math.AG2023
The cycle class of the supersingular locus of principally polarized abelian varieties
Gerard van der Geer, Shushi Harashita
We prove a formula for the cycle class of the supersingular locus in the Chow ring with rational coefficients of the moduli space of principally polarized abelian varieties in char…