On the $K$-theory of the $p$-adic unit disk

Abstract

In this note, we study the $p$-complete topological cyclic homology of the affine line relative to a ring $A$ which is smooth over a perfectoid ring $R$. Denoting by $NTC(A;{\mathbb{Z}}_p)$ the spectrum which measures the failure of ${\mathbb{A}}^1$-invariance on $A$, we observe a kind of Quillen-Lichtenbaum phenomena for $NTC(A;{\mathbb{Z}}_p)$ -- that it is isomorphic to its own $K(1)$-localization in a specified range of degrees which depends on the relative dimension of $A$. Somewhat surprisingly, this range is better than considerations following from a theorem of Bhatt-Mathew and étale-to-syntomic comparisons. Via the Dundas-Goodwillie-McCarthy theorem, we obtain a description of the algebraic $K$-theory of $p$-completed affine line over such rings.

13 pages, comments welcome