Siegel modulator form (mod p) and algebraic modular forms

Abstract

In his letter [Ser96], J.-P. Serre proves that the systems of Hecke eigenvalues given by modular forms (mod p) are the same as the ones given by locally constant functions ... , where B is the endomorphism algebra of a supersingular elliptic curve. After giving a detailed exposition of Serre's result, we prove that the systems of Hecke eigenvalues given by Siegel modular forms (mod p) of genus g are the same as the ones given by algebraic modular forms (mod p) on the group GUg(B), as defined in [Gro99] and [Gro98]. The correspondence is obtained by restricting to the superspecial locus of the moduli space of abelian varieties.