Braided autoequivalences and quantum commutative bi-Galois objects

Abstract

Let $(H,R)$ be a quasitriangular weak Hopf algebra over a field $k$. We show that there is a braided monoidal equivalence between the Yetter-Drinfeld module category $^H_H\mathscr{YD}$ over $H$ and the category of comodules over some braided Hopf algebra ${}_RH$ in the category $_H\mathscr{M}$. Based on this equivalence, we prove that every braided bi-Galois object $A$ over the braided Hopf algebra ${}_RH$ defines a braided autoequivalence of the category $^H_H\mathscr{YD}$ if and only if $A$ is quantum commutative. In case $H$ is semisimple over an algebraically closed field, i.e. the fusion case, then every braided autoequivalence of $^H_H\mathscr{YD}$ trivializable on $_H\mathscr{M}$ is determined by such a quantum commutative Galois object. The quantum commutative Galois objects in $_H\mathscr{M}$ form a group measuring the Brauer group of $(H,R)$ as studied in [20] in the Hopf algebra case.