Generic vanishing on homogeneous spaces in arbitrary characteristic

Abstract

Let $X$ be a proper homogeneous space for a connected algebraic group $G$ over an algebraically closed field. For locally closed smooth affine subvarieties $W,Z\subset X$, we show that \[ (-1)^{\dim X-\dim W+\dim Z}χ(gW\cap Z)\geq 0 \] for generic $g\in G$. This extends the characteristic-zero theorem of Schürmann--Simpson--Wang. Over finite fields, our methods give a trace-function identity on a dense open subset of $G$ and a Lang--Weil estimate for the non-generic locus.

18 pages. v2: new section on arithmetic corollaries and modified title