Endomorphisms of Fano 3-folds and log Bott vanishing

Abstract

Kawakami and the author showed that a projective variety with an int-amplified endomorphism of degree invertible in the base field satisfies Bott vanishing. That was a new way to analyze which varieties have nontrivial endomorphisms. In this paper, we extend that result to a logarithmic version of Bott vanishing for an endomorphism with a totally invariant divisor. We apply this to Fano 3-folds. Meng-Zhang-Zhong showed that the only smooth complex Fano 3-folds that admit an int-amplified endomorphism are the toric ones. Also, Achinger-Witaszek-Zdanowicz showed that the only smooth complex Fano 3-folds that are images of toric varieties are the toric ones. Using log Bott vanishing, we reprove both results and extend them to characteristic p, for morphisms of degree prime to p.