Topological defect lines provide a powerful framework for characterizing symmetries and dualities in two-dimensional conformal field theories. In fermionic CFTs, however, the conventional notion of symmetry as a group action is no longer sufficient. In this talk, I will explain how topological defect lines in fermionic CFTs naturally lead to a generalized notion of symmetry, encoded not by an fusion category in a bosonic theory but by a superfusion category.

Fengjun Xu is currently an Assistant Professor at the Beijing Institute of Mathematical Sciences and Applications (BIMSA). His research interests lie in string theory and related problems. He obtained his Ph.D. from Heidelberg University in 2019. After that, He remained as a research fellow in ITP, Heidelberg University until 2021. Then he moved to YMSC, Tsinghua University and BIMSA as a postdoc Researcher.