On the Seshadri constants of equivariant bundles over Bott-Samelson varieties and wonderful compactifications

Abstract

We study torus-equivariant vector bundles $E$ on a complex projective variety $X$ which is either a Bott-Samelson-Demazure-Hansen variety or a wonderful compactification of a complex symmetric variety of minimal rank. We show that $E$ is nef (respectively, ample) if and only if its restriction to every torus--invariant curve in $X$ is nef (respectively, ample). We also compute the Seshadri constants $\epsilon (E,x)$, where $x\in X$ is any point fixed by the action of a maximal torus.

arXiv comment15 pages; final version; to appear in manuscripta mathematica