Twisted cotangent sheaves and a Kobayashi-Ochiai theorem for foliations

Abstract

Let X be a normal projective variety, and let A be an ample Cartier divisor on X. We prove that the twisted cotangent sheaf $\Omega_X \otimes A$ is generically nef with respect to the polarisation A unless X is a projective space. As an application we prove a Kobayashi-Ochiai theorem for foliations: if $F \subsetneq T_X$ is a foliation of rank r such that $det F \equiv i_F A$, then we have $i_F \leq r$.