$\otimes$-Frobenius functors and exact module categories (2501.16978v1)

Abstract: We call a tensor functor $F:\mathcal{C}\rightarrow\mathcal{D}$ between finite tensor categories $\otimes$-Frobenius if the left and right adjoints of $F$ are isomorphic as $\mathcal{C}$-bimodule functors. We provide various characterizations of $\otimes$-Frobenius functors such as the unimodularity of the centralizer $\mathcal{Z}({}_F\mathcal{D}_F)$. We analyze the procedure of pulling back actions of tensor categories on module categories along tensor functors, and show that properties like pivotality and unimodularity are preserved if and only if $F$ if $\otimes$-Frobenius. These results allow the transport of Frobenius algebras under certain conditions. We apply the results to internal natural transformations and examples coming from Hopf algebras.