Construction of algebraic covers

TL;DR

This paper investigates the local algebraic properties of sheaves that define algebraic covers of varieties, with a focus on Gorenstein covers of degree 6 related to deformations of S3-Galois branch covers.

Contribution

It introduces a framework for analyzing sheaves of ideals defining algebraic covers and studies Gorenstein degree 6 covers with specific decompositions, extending prior work on triple covers.

Findings

Characterization of sheaves defining algebraic covers.

Analysis of Gorenstein degree 6 covers with orthogonal decompositions.

Connection to deformations of S3-Galois branch covers.

Abstract

Let $Y$ be an algebraic variety, $\mathcal{F}$ a locally free sheaf of $\mathcal{O}_Y$-modules, and $\mathcal{R}(\mathcal{F})$ the $\mathcal{O}_Y$-algebra $\operatorname{Sym}^\bullet \mathcal{F}$. In this paper we study local properties of sheaves of $\mathcal{O}_{\mathcal{R}(\mathcal{F})}$-ideals $\mathcal{I}$ such that $\mathcal{R}(\mathcal{F}))/\mathcal{I}$ is an algebraic cover of $Y$. Following the work of Miranda for triple covers, for $\mathcal{Q}$ a direct summand of $\mathcal{R}(\mathcal{F})$, we say that a morphism $\Phi\colon \mathcal{Q}\rightarrow\mathcal{R}(\mathcal{F})/\langle\mathcal{Q}\rangle$ is a covering homomorphism if it induces such an ideal. As an application we study in detail the case of Gorenstein covering maps of degree $6$ for which the direct image of $\varphi_*\mathcal{O}_X$ admits an orthogonal decomposition. These are deformation of $S_3$-Galois branch covers.