The zero section of the universal semiabelian variety, and cycles on the moduli space of marked curves

The moduli space of abelian varieties admits a natural partial compactification, due to Mumford,
by semi-abelic varieties of torus rank one. We calculate the class of the zero section of the partial
compactification in the Chow ring. We also discuss the Abel-Jacobi map from the moduli space
of marked curves to the moduli space of abelian varieties, and induced relations in the
tautological ring of curves. Joint work with Samuel Grushevsky.