Module categories, internal bimodules and Tambara modules

Abstract

We use the theory of Tambara modules to extend and generalize the reconstruction theorem for module categories over a rigid monoidal category to the non-rigid case. We show a biequivalence between the $2$-category of cyclic module categories over a monoidal category $\mathscr{C}$ and the bicategory of algebra and bimodule objects in the category of Tambara modules on $\mathscr{C}$. Using it, we prove that a cyclic module category can be reconstructed as the category of certain free module objects in the category of Tambara modules on $\mathscr{C}$, and give a sufficient condition for its reconstructability as module objects in $\mathscr{C}$. To that end, we extend the definition of the Cayley functor to the non-closed case, and show that Tambara modules give a proarrow equipment for $\mathscr{C}$-module categories, in which $\mathscr{C}$-module functors are characterized as $1$-morphisms admitting a right adjoint. Finally, we show that the $2$-category of all $\mathscr{C}$-module categories embeds into the $2$-category of categories enriched in Tambara modules on $\mathscr{C}$, giving an ''action via enrichment'' result.