On the indecomposability of a remarkable new family of modules appearing in Galois theory

Abstract

A powerful new perspective in the analysis of absolute Galois groups has recently emerged from the study of Galois modules related to classical parameterizing spaces of certain Galois extensions. The recurring trend in these decompositions is their stunning simplicity: almost all summands are free over some quotient ring. The non-free summands which appear are exceptional not only because they are different in form, but because they play the key role in controlling arithmetic conditions that allow the remaining summands to be easily described. In this way, these exceptional summands are the lynchpin for a bevy of new properties of absolute Galois groups that have been gleaned from these surprising decompositions. In one such recent decomposition, a remarkable new exceptional summand was discovered which exhibited interesting properties that have not been seen before. The exceptional summand is drawn from a particular finite family that has not yet been investigated. The main goal of this paper is to introduce this family of modules and verify their indecomposability. We believe this module will be of interest to people working in Galois theory, representation theory, combinatorics, and general algebra. The analysis of these modules includes some interesting new tools, including analogs of $p$-adic expansions.

v1: 36 pages. v2: 38 pages, includes results on necessity of conditions from main theorem. v3: 38 pages, final version as it will appear in Journal of Algebra

References in corpus (5)

• Galois module structure of pth-power classes of cyclic extensions of degree p^n
• Galois module structure of square power classes for biquadratic extensions
• Galois module structure of Milnor K-theory mod p^s in characteristic p
• Cohomology of algebraic groups, finite groups, and Lie algebras: Interactions and Connections
• Detecting pro-p-groups that are not absolute Galois groups

Cited by in corpus (1)

• Arithmetic properties encoded in the Galois module structure of $K^{\times }/K^{\times p^m}$