Homomorphisms and rigid isomorphisms of twisted group doubles

Abstract

We prove several results concerning quasi-bialgebra morphisms $\mathcal{D}^\omega(G)\to\mathcal{D}^\eta(H)$ of twisted group doubles. We take a particular focus on the isomorphisms which are simultaneously isomorphisms $\mathcal{D}(G)\to\mathcal{D}(H)$. All such isomorphisms are shown to be morphisms of quasi-Hopf algebras, and a classification of all such isomorphisms is determined. Whenever $\omega\in Z^3(G/Z(G),U(1))$ this suffices to completely describe $\operatorname{Aut}(\mathcal{D}^\omega(G))$, the group of quasi-Hopf algebra isomorphisms of $\mathcal{D}^\omega(G)$, and so generalizes existing descriptions for the case where $\omega$ is trivial.