Subalgebras of etale algebras and fusion subcategories

Abstract

In \cite[Rem. 3.4]{DNO} the authors asked the question if any étale subalgebra of an étale algebra in a braided fusion category is also étale. We give a positive answer to this question if the braided fusion category $\cc$ is pseudo-unitary and non-degenerate. In the case of a pseudo-unitary fusion category we also give a new description of the lattice correspondence from \cite[Theorem 4.10]{DMNO}. This new description enables us to describe the two binary operations on the lattice of fusion subcategories.

arXiv comment35 pages. Comments are welcome! Subsection 4.5 has been added. Corrected typos