Abstract

We study the cohomology of the moduli space of genus three curves with level two structure and some related spaces. In particular, we determine the cohomology groups of the moduli space of plane quartics with level two structure as representations of the symplectic group on a six dimensional vector space over the field of two elements. We also make the analogous computations for some related spaces such as moduli spaces of genus three curves with a marked point and strata of the moduli space of Abelian differentials of genus three.

Highlights

  • The purpose of this note is to compute the de Rham cohomology of various moduli spaces of curves of genus 3 with level 2 structure

  • The cohomology groups become Sp(6, F2)-representations and our goal is to describe these cohomology groups as representations together with their mixed Hodge structure

  • We have the moduli space Hol 3[2] of genus 3 curves with level 2 structure marked with a holomorphic (i.e. Abelian) differential and some related spaces, e.g. the moduli space of genus 3 curves marked with a canonical divisor

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Summary

Introduction

The purpose of this note is to compute the de Rham cohomology of various moduli spaces of curves of genus 3 with level 2 structure. The group Sp(6, F2) acts on the set of level 2 structures of a curve This action induces actions on the various moduli spaces under consideration which in turn yields actions on the cohomology groups. We have the moduli space M3[2] of genus 3 curves with level 2 structure and some natural loci therein. This will be our main object of study. There are many constructions, some classical and some new, relating the various spaces and which will provide essential information for our cohomological computations

Outline
Notations and conventions
Background
Level structures
Curves of genus three
Point configurations in the projective plane
Genus three curves with marked points
Del Pezzo surfaces of degree two with marked points
The irreducible nodal case
The other cases
Cohomological computations
Moduli of canonical divisors
Cohomology of moduli spaces of Abelian differentials
The weighted Euler characteristic
Full Text
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