Commutants in crossed product algebras for piecewise constant functions on the real line

TL;DR

This paper investigates the structure of commutants in crossed product algebras formed by piecewise constant functions on the real line under integer group actions, focusing on how changes in partitions affect these commutants.

Contribution

It provides a detailed analysis of the commutants in crossed product algebras for piecewise constant functions, especially regarding how modifications in partitions influence the algebraic structure.

Findings

Characterization of commutants for algebras with fixed jump points

Analysis of how adding or removing jump points alters the commutants

Complete description of the difference between commutants for refined partitions

Abstract

In this paper we consider commutants in crossed product algebras, for algebras of piece-wise constant functions on the real line acted on by the group of integers $\mathbb{Z}$. The algebra of piece-wise constant functions does not separate points of the real line, and interplay of the action with separation properties of the points or subsets of the real line by the function algebra become essential for many properties of the crossed product algebras and their subalgebras. In this article, we deepen investigation of properties of this class of crossed product algebras and interplay with dynamics of the actions. We describe the commutants and changes in the commutants in the crossed products for the canonical generating commutative function subalgebras of the algebra of piece-wise constant functions with common jump points when arbitrary number of jump points are added or removed in general positions, that is when corresponding constant value sets partitions of the real line change, and we give complete characterization of the set difference between commutants for the increasing sequence of subalgebras in crossed product algebras for algebras of functions that are constant on sets of a partition when partition is refined.