Formal Brauer groups and the moduli of abelian surfaces

Abstract

In this paper we consider the stratification on the moduli space of principally polarized abelian surfaces in characteristic $p>0$ defined by the height of the formal group associated to $H^2(X,O_X)$. We compute the cycle classes of the strata and compare these with those of the $p$-rank stratification.

Latex, 27 pages, minor correction in section 9