Fusing binary interface defects in topological phases: The Z/pZ case

A binary interface defect is any interface between two (not necessarily invertible) domain walls. We compute all possible binary interface defects in Kitaev's Z/pZ model and all possible fusions between them. Our methods can be applied to any Levin-Wen model. We also give physical interpretations for each of the defects in the Z/pZ model. These physical interpretations provide a new graphical calculus, which can be used to compute defect fusion.