Fusing Binary Interface Defects in Topological Phases: The $\mathrm{Vec}(\mathbb{Z}\mathrm{/}p\mathbb{Z})$ 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 $\mathbb{Z}\mathrm{/}p\mathbb{Z}$ 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 $\mathbb{Z}\mathrm{/}p\mathbb{Z}$ model. These physical interpretations provide a new graphical calculus which can be used to compute defect fusion.