Verschiebung maps among $K$-groups of truncated polynomial algebras

Abstract

Let $p$ be a prime number, and let $A$ be a ring in which $p$ is nilpotent. In this paper, we consider the maps $$K_{q+1}(A[x]/(x^m),(x))\to K_{q+1}(A[x]/(x^{mn}),(x)),$$induced by the ring homomorphism $A[x]/(x^m)\to A[x]/(x^{mn})$, $x\mapsto x^n$. We evaluate these maps, up to extension, for general $A$ in terms of topological Hochschild homology, and for regular ${\mathbb{F}}_p$-algebras $A$, in terms of groups of de Rham-Witt forms. After the evaluation, we give a calculation of the relative $K$-group of ${\mathcal{O}}_K/p{\mathcal{O}}_K$ for certain perfectoid fields $K$.

Corollary 4.7 in the previous version is deleted. Two new corollaries are added