Talk

We define a general class of "crystallographic" sphere packings, and study the subclass of "superintegral" such. We prove an "arithmeticity" theorem, connecting these to the theory of hyperbolic arithmetic reflection lattices. As a consequence, superintegral packings only exist in finitely many dimensions, and in fact in finitely many commensurability classes, in principle allowing for a complete classification.

We show that the dynamics of endomorphisms of abelian varieties (e.g., elliptic curves) over field of characteristic $p>0$ is sharply divided according to two possible scenario’s, reflected in properties of the Artin-Mazur zeta function (transcendental/rational) and orbit growth, somewhat similar to the mixing/non-mixing dichotomy in measurable dynamics. The two scenario’s are distinguished by the action on the $p$-torsion subgroup scheme.

A Teichmuller curve is a totally geodesic curve in the moduli space of Riemann surfaces. These curves are defined by polynomials with integer coefficients which are irreducible over $\mathbb C$. We will show that these polynomials have surprising factorizations mod $p$.  This is joint work with Keerthi Madapusi Pera.