A Mehta-Ramanathan theorem for linear systems with basepoints

Abstract

Let $(X, H)$ be a normal complex projective polarized variety and $\mathscr E$ an $H$-semistable sheaf on $X$. We prove that the restriction $\mathscr E\big|_C$ to a sufficiently positive general complete intersection curve $C \subset X$ passing through a prescribed finite set of points $S \subset X$ remains semistable, provided that at each $p \in S$, the variety $X$ is smooth and the factors of a Jordan-H\"older filtration of $\mathscr E$ are locally free. As an application, we obtain a generalization of Miyaoka's generic semipositivity theorem.