Uniformity and isotypic smallness for quantum-group representations

Abstract

Compact-group representations on Banach spaces are known to be norm-continuous precisely when they have finite spectra. For a quantum group with continuous-function algebra $\mathcal{C}(\mathbb{G})$ norm continuity can be cast analogously as the bounded weak${}^{\ast }$-norm continuity of the representation's attached maps $\mathcal{C}(\mathbb{G}{)}^{\ast }\to \mathrm{End}(E)$ and its mirror counterpart $E_{\le 1}\times E_{\le 1}^{\ast }\to \mathcal{C}(\mathbb{G})$. While the uniformity/isotypic finiteness equivalence no longer holds generally, it does (for the latter map) for compact quantum groups either coamenable or having dimension-bounded irreducible representations. This generalizes the aforementioned classical variant, providing two independent quantum-specific mechanisms of recovering it.

v2 reorganizes and reworks much of the material after feedback; 8 pages + references