Transport across interfaces in symmetric orbifolds

A general classification of conformal interfaces has long been lacking in the literature. One approach is to map interfaces to conformal boundaries, then to use the tools of boundary CFT to extract specific physical data encoded by an associated boundary state. Guided by this, we examine how boundary states encode energy transport coefficients -- i.e. transmission and reflection probabilities -- of the related conformal interfaces in symmetric orbifold theories, which constitute a large class of irrational theories and are closely related to holographic setups. At the orbifold point, we find that the transport coefficients are only informed by untwisted-sector terms in the boundary states and so are averages of coefficients in the underlying seed theory. Following that, we then study the symmetric orbifold of the $\mathbb{T}^4$ sigma model ICFT dual to type IIB supergravity on the 3d Janus solution. The Janus solution can be used to compute transport coefficients of particular interfaces in the strongly coupled regime of the symmetric orbifold theory (far from the orbifold point). We compare these coefficients to that of the free theory, finding that the profile of the transmission coefficient changes functionally and overall increases with the coupling.