Keel’s base point free theorem and quotients in mixed characteristic

Abstract

We develop techniques of mimicking the Frobenius action in the study of universal homeomorphisms in mixed characteristic. As a consequence, we show a mixed characteristic Keel’s base point free theorem obtaining applications towards the mixed characteristic Minimal Model Program, we generalise Kollár’s theorem on the existence of quotients by finite equivalence relations to mixed characteristic, and we provide a new proof of the existence of quotients by affine group schemes.