Lefschetz filtration and Perverse filtration on the compactified Jacobian

TL;DR

This paper proves that the Lefschetz and perverse filtrations on the cohomology of the compactified Jacobian of a complex curve with planar singularities are opposite, confirming a conjecture by Maulik-Yun.

Contribution

It establishes the opposition of Lefschetz and perverse filtrations on the cohomology of the compactified Jacobian, confirming a conjecture in the context of singular curves.

Findings

Lefschetz and perverse filtrations are opposite on $H^*(J)$

The result confirms Maulik-Yun's conjecture

Provides a geometric proof for the relationship between the filtrations

Abstract

Let $C$ be a complex integral curve with plannar singularities. Let $J$ be the compactified Jacobian of $C$. There are two filtrations on the cohomology group $H^*(J)$. One is obtained by the nilpotent morphism defined by cupping a certain ample divisor on $J$, which we call the Lefschetz filtration. To obtain the other filtration, we put $C$ into a family of curves $\mathcal{C}\rightarrow B$ so that $J$ can be embedded into a family $f:\mathcal{J}\rightarrow B$, and we let $B, \mathcal{C},\mathcal{J}$ be smooth. Then $Rf_*(\mathbb{Q}_{\mathcal{J}})$ decomposes into a direct sum of its (shifted) perverse cohomologies. Restricting this decomposition to fibers, we get a filtration on $H^*(J)$ called the perverse filtration. We show in this paper that these two filtrations are opposite to each other as conjectured by Maulik-Yun.