A minimal single brane holographic model can be used as a dual to 2d conformal interfaces (ICFTs) to calculate the transmission coefficient $$ \mathcal{T} $$ T of energy transported across the defect as well as boundary entropy log g, the additional entanglement entropy for some sub-region that encloses the defect. Both $$ \mathcal{T} $$ T and log g are uniquely determined by the tension characterizing the brane. In contrast, in field theory defects typically the transmission coefficient can be dialed from 0 to 1 independently for each allowed value of log g. To address this discrepancy, we look at a double brane (3-region bulk) holographic model. Merger of two single brane interfaces creates genuinely new interfaces which indeed allow a range of accessible transmission coefficients for a fixed value of log g. In particular, the $$ \mathcal{T} $$ T = 0 limit of two completely decoupled BCFTs can be achieved.

One characteristic feature of many fractonic lattice models, and a defining property of the exotic field theories developed to describe them, are subsystem symmetries including a conservation of not just net electric charge but also electric dipole moments or charges living on submanifolds. So far all such theories were based on internal subsystem symmetries. In this work we generalize the notion of subsystem symmetries to system with subsystem spacetime symmetries with locally conserved energies.

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 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.