| Summary: | Large black holes in anti-de Sitter space have positive specific heat and do
not evaporate. In order to mimic the behavior of evaporating black holes, one
may couple the system to an external bath. In this paper we explore a rich
family of such models, namely ones obtained by coupling two holographic CFTs
along a shared interface (ICFTs). We focus on the limit where the bulk solution
is characterized by a thin brane separating the two individual duals. These
systems may be interpreted in a double holographic way, where one integrates
out the bath and ends up with a lower-dimensional gravitational braneworld dual
to the interface degrees of freedom. Our setup has the advantage that all
observables can be defined and calculated by only relying on standard rules of
AdS/CFT. We exploit this to establish a number of general results, relying on a
detailed analysis of the geodesics in the bulk. Firstly, we prove that the
entropy of Hawking radiation in the braneworld is obtained by extremizing the
generalized entropy, and moreover that at late times a so-called `island
saddle' gives the dominant contribution. We also derive Takayanagi's
prescription for calculating entanglement entropies in BCFTs as a limit of our
ICFT results.
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