The Chow ring of the moduli space of genus 6 curves

Ravi Vakil, November 12th, 2013

We determine the Chow ring (with rational coefficients) of the moduli space of curves of
genus 6 by showing that all Chow classes are tautological. In particular, all algebraic
cohomology is tautological, and the natural map from Chow to cohomology is injective.
We rely on results of many others, notably Faber, Vistoli, and Mukai. To show the efficacy
of these methods, we give quick derivations of the Chow groups of moduli spaces of
curves of lower genus as well. What makes the genus 6 argument tractable (and even
short) is the particularly beautiful Brill-Noether theory in this case. This is joint work with
Nikola Penev.