|DATE||October 22 (Mon), 2018|
|TITLE||Discrete gauge anomalies revisited|
Cancellation of gauge anomalies is a fundamental constraint on a consistent quantum field theory. While anomalies of continuous symmetries such as U(1) are well understood, the cases of discrete symmetries have been studied much less. In this talk, we revisit discrete gauge anomalies in chiral fermion theories in 3 + 1 dimensions --- from a more modern perspective based on the concept of symmetry protected topological (SPT) phases. We focus on the simplest case that the discrete internal symmetries are cyclic groups. A reformulation of the "discrete anomaly cancellation" conditions, first proposed by Ib??ez and Ross in 1991 , is given. Also, the role of symmetry extensions in discrete anomalies is clarified in a formal fashion. Therefore, our work provides a fundamental and complete understanding of discrete symmetry anomalies, respecting the viewpoint in the work of Banks and Dine .