Reflections of Symmetry: Defects, Anomalies, and Unusual Scattering

Abstract

Defects and boundaries play an important role in a wide range of physical contexts, from particle physics to critical phenomena. In this talk, I will discuss how bulk symmetries can be realized in subtle ways in the presence of such impurities, introducing the concepts of symmetry reflecting defects and defect anomalies. I will focus on two main applications. First, I will demonstrate how these symmetry considerations can impose strong constraints on the long-distance dynamics. Second, I will show how they provide a natural explanation for scattering processes whose outgoing states appear to carry unusual quantum numbers. These phenomena can be understood and systematically predicted from topological considerations, in a variety of examples including massive theories.