On the Mori theory of Bott-Samelson varieties

Georg Merz, David Schmitz, Henrik Seppänen

Published 2017-09-28Version 1

We prove that on a Bott-Samelson variety X every movable divisor is nef. This enables us to consider Zariski decompositions of effective divisors, which in turn yield a description of the Mori chamber decomposition of the effective cone. This amounts to information on all possible birational morphisms from X. We illustrate our findings by two concrete examples.