Lefschetz filtration and Perverse filtration on the compactified Jacobian

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 $H^{\ast }(J)$. 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 $\mathcal{C}\to B$ so that $J$ can be embedded into a family $f:\mathcal{J}\to B$, and we let $B,\mathcal{C},\mathcal{J}$ be smooth. Then $R{f}_{\ast }({\mathbb{Q}}_{\mathcal{J}})$ decomposes into a direct sum of its (shifted) perverse cohomologies. Restricting this decomposition to fibers, we get a filtration on $H^{\ast }(J)$ called the perverse filtration. We show in this paper that these two filtrations are opposite to each other as conjectured by Maulik-Yun.