Coverings of skew-products and crossed products by coactions

Abstract

Consider a projective limit G of finite groups G_n. Fix a compatible family \delta^n of coactions of the G_n on a C*-algebra A. From this data we obtain a coaction \delta of G on A. We show that the coaction crossed product of A by \delta is isomorphic to a direct limit of the coaction crossed products of A by the \delta^n. If A = C*(\Lambda) for some k-graph \Lambda, and if the coactions \delta^n correspond to skew-products of \Lambda, then we can say more. We prove that the coaction crossed-product of C*(\Lambda) by \delta may be realised as a full corner of the C*-algebra of a (k+1)-graph. We then explore connections with Yeend's topological higher-rank graphs and their C*-algebras.Comment: 19 pages, laTeX. v2: Minor modifications to version 1. This version to appear in the Journal of the Australian Mathematical Society v3: some potentially confusing typos corrected in the proof of Theorem~3.1, as well as a few others. References update