Title: Severi varieties and the moduli space of curves
Description: We study Severi varieties parameterizing genus g curves in a fixed divisor class on a rational surface. Corresponding to every such variety, there is a one-parameter family of genus g stable curves whose numerical invariants we compute. Building on the work of Caporaso and Harris, as well as Vakil, we derive a recursive formula for the degrees of the Hodge bundle on the families in question. In the case when a surface is isomorphic to [Special characters omitted.] , we produce moving curves in the moduli space M g of Deligne-Mumford stable curves. We use these to derive lower bounds on the slopes of effective divisors on M g . Another application of our results is to various enumerative problems for planar curves.