The Chow ring of $\mathcal{S}_5^-$ is tautological

Abstract

The moduli spaces $\mathcal{S}_g^-$ parametrise odd spin curves of genus $g$. These are pairs $[C, \eta]$ where $C$ is a smooth genus $g$ curve of and $\eta$ is a line bundle on $C$ such that $\eta^{\otimes 2} = \omega_C$ and $h^0(C, \eta)$ is odd. The main result of this work is the tautology of the Chow ring of $\mathcal{S}_5^-$. Our method of proof revolves around an analysis of the geometry of canonical genus 5 curves and totally tangent hyperplanes. In the course of establishing our main result, we also prove the rationality of the closely related differential stratum in $\mathcal{M}_{5, 4}$ dominating $\mathcal{S}_5^-$.