The classical notion of a dagger structure enters physics for instance in certain formalizations of unitary quantum mechanics or in the description of very simple topological D-branes in orientifolds. More generally, the theory of higher dagger structures is meant to encode some of the rich structure of unitarity and defects in arbitrary (topological) quantum field theories. We aim to keep our account elementary; no prior knowledge of higher category theory will be assumed.
Tim Lüders (Vienna): An Informal Introduction to Higher Dagger Structures
