On the growth of even $K$-groups of rings of integers in $p$-adic Lie extensions

TL;DR

This paper investigates the growth of even K-groups' Sylow p-subgroups in p-adic Lie extensions of rings of integers, extending previous cyclotomic results using Iwasawa cohomology and the Quillen-Lichtenbaum Conjecture.

Contribution

It introduces a new approach via Iwasawa cohomology to study K-group growth in general p-adic Lie extensions, beyond cyclotomic cases.

Findings

Generalizes previous results to broader p-adic Lie extensions

Establishes conditions for torsionness of Iwasawa cohomology groups

Provides examples with nontrivial μ-invariants in second Iwasawa cohomology

Abstract

Let $p$ be an odd prime number. In this paper, we study the growth of the Sylow $p$-subgroups of the even $K$-groups of rings of integers in a $p$-adic Lie extension. Our results generalize previous results of Coates and Ji-Qin, where they considered the situation of a cyclotomic $\mathbb{Z}_p$-extension. Our method of proof differs from these previous work. Their proof relies on an explicit description of certain Galois group via Kummer theory afforded by the context of a cyclotomic $\mathbb{Z}_p$-extension, whereas our approach is via considering the Iwasawa cohomology groups with coefficients in $\mathbb{Z}_p(i)$ for $i\geq 2$. We should mention that this latter approach is possible thanks to the Quillen-Lichtenbaum Conjecture which is now known to be valid by the works of Rost-Voevodsky. We also note that the approach allows us to work with more general $p$-adic Lie extensions that do not necessarily contain the cyclotomic $\mathbb{Z}_p$-extension, where the Kummer theoretical approach does not apply. Along the way, we study the torsionness of the second Iwasawa cohomology groups with coefficients in $\mathbb{Z}_p(i)$ for $i\geq 2$. Finally, we give examples of $p$-adic Lie extensions, where the second Iwasawa cohomology groups can have nontrivial $\mu$-invariants.