Equivariant Parabolic connections and stack of roots

TL;DR

This paper constructs and studies $G$-equivariant structures on stacks of roots of line bundles over varieties with group actions, establishing an equivalence between equivariant logarithmic and parabolic connections.

Contribution

It introduces $G$-equivariant structures on stacks of roots and proves an equivalence between categories of $G$-equivariant logarithmic and parabolic connections.

Findings

Lift of $G$-action to stacks of roots under certain conditions

Existence of $G$-linearization of the tautological sheaf

Equivalence between $G$-equivariant logarithmic and parabolic connections

Abstract

Let $X$ be a smooth complex projective variety equipped with an action of a linear algebraic group $G$ over $\mathbb{C}$. Let $D$ be a reduced effective divisor on $X$ that is invariant under the $G$--action on $X$. Let $s_D$ be the canonical section of $\mathcal{O}_X(D)$ vanishing along $D$. Given a positive integer $r$, consider the stack $\mathfrak{X} := \mathfrak{X}_{(\mathcal{O}_X(D),\, s_D,\, r)}$ of $r$-th roots of $(\mathcal{O}_X, s_D)$ together with the natural morphism $\pi : \mathfrak{X} \to X$. Under the assumption that $G$ has no non-trivial characters, we show that the $G$--action on $X$ naturally lifts to a $G$--action on $\mathfrak{X}$ such that $\pi$ become $G$--equivariant, and the tautological invertible sheaf $\mathscr{M}$ on $\mathfrak{X}$ admits a linearization of this $G$--action. Finally, we define the notions of $G$--equivariant logarithmic connections on $\mathfrak{X}$ and $G$--equivariant parabolic connections on $X$ with rational parabolic weights along $D$, and establish an equivalence between the category of $G$--equivariant logarithmic connections on $\mathfrak{X}$ and the category of $G$--equivariant parabolic connections on $X$ with rational parabolic weights along $D$.