Lifting iterated Frobenius over $W_n(k)$

TL;DR

This paper develops a modified theory for lifting the (n-1)th iterated Frobenius morphism of smooth schemes over perfect fields, extending previous work on infinitesimal Frobenius liftings and their obstructions.

Contribution

It introduces a new approach to lift the (n-1)th iterated Frobenius directly over Witt rings, refining the understanding of Frobenius liftings and their obstructions.

Findings

Provides a modified framework for Frobenius lifting theory.

Identifies new obstruction classes for iterated Frobenius liftings.

Extends previous results to higher iterates of Frobenius.

Abstract

Let $X$ be a smooth scheme over a perfect field $k$ of positive characteristic. M.V.~Nori and V.~Srinivas studied infinitesimal liftings of Frobenius morphism $F:X\to X$. Namely, given a Frobenius lifting $F_Y: Y\to Y$ over $W_{n-1}(k)$ the obstruction of lifting $F_Y$ over $W_n(k)$ is a class in $H^1(X, T_X\tensor B_1\Omega^1_{X/k})$. We give a modified version of their theory and applications, in which we consider lifting $(n-1)$th iterated Frobenius $F^{n-1}:X\to X$ directly over $W_n(k)$.