Twisted partial group algebra and related topological partial dynamical system

TL;DR

This paper constructs a topological partial dynamical system from a group and a factor set, representing the twisted partial group algebra as a crossed product, and analyzes conditions for topological freeness affecting the algebra's structure.

Contribution

It introduces a new realization of twisted partial group algebras as crossed products with a topological partial dynamical system, extending previous results to more general settings.

Findings

Realization of twisted partial group algebra as a crossed product.

Conditions for topological freeness of the spectral partial action.

Decomposition of algebra into matrix algebras over twisted subgroup algebras when discrete.

Abstract

Given a group \( G \), a field \( \kappa \), and a factor set \( \sigma \) arising from a partial projective \( \kappa \)-representation of \( G \). This leads to the construction of a topological partial dynamical system \( (\Omega_\sigma, G, \hat{\theta}) \), where \( \Omega_\sigma \) is a compact, totally disconnected Hausdorff space, and \( \sigma \) acts as a twist for \( \hat{\theta} \). We show that the twisted partial group algebra \( \kappa_{par}^{\sigma} G \) can be realized as a crossed product \( {\mathscr L}(\Omega_\sigma) \rtimes_{(\hat{\theta}, \sigma)} G \), with \( {\mathscr L}(\Omega_\sigma) \) denoting the \( \kappa \)-algebra of locally constant functions \( \Omega_\sigma \to \kappa \). The space \( \Omega_\sigma \) corresponds to the spectrum of a unital commutative subalgebra in \( \kappa_{par}^{\sigma} G \), generated by idempotents. By describing \( \Omega_\sigma \) as a subspace of the Bernoulli space \( 2^G \), we examine conditions under which the spectral partial action \( \hat{\theta} \) is topologically free, impacting the ideal structure of \( \kappa_{par}^{\sigma} G \). We further explore generating idempotent factor sets of \( G \) and present conditions on them to ensure the topological freeness of \( \hat{\theta} \). Inspired by Exel's semigroup \( \mathcal{S}(G) \), which governs partial actions and representations of \( G \) and relates to \( \kappa_{par}G \), we characterize the twisted partial group algebra \( \kappa_{par}^{\sigma}G \) as generated by a \( \kappa \)-cancellative inverse semigroup constructed from elements of \( \Omega_\sigma \). When \( \Omega_\sigma \) is discrete, we demonstrate that \( \kappa_{par}^{\sigma} G \) decomposes into a product of matrix algebras over twisted subgroup algebras, generalizing known results for finite \( G \).