Defects extremal surfaces and interface CFTs
arXiv:2607.15083
The paper extends the defect extremal surface prescription to holographic interface CFTs, showing it matches lower-dimensional island formula results for entanglement entropy and computes Page curves for radiation coupled to 2D black holes.
Abstract
We propose a generalization of the defect extremal surface (DES) prescription to holographic interface conformal field theories (ICFTs), extending its applicability beyond the AdS/BCFT framework. We consider a holographic ICFT comprising two CFTs coupled across an interface, dual to two asymptotically AdS geometries joined by a codimension-one end-of-the-world (EOW) brane. In the corresponding effective lower-dimensional description obtained via partial dimensional reduction on the brane-boundary combination, the theory on the brane is coupled to gravity, thereby enabling the computation of fine-grained entanglement entropy via the island formula. We demonstrate that the generalized DES prescription exactly reproduces the effective lower-dimensional results for finite subsystems in time-independent scenarios in the large brane tension limit, corresponding to weak gravitational coupling on the EOW brane. We further compute the entanglement entropy of semi-infinite bipartite pure states in radiation subsystems coupled to eternal black holes, and obtain the corresponding Page curves.
30 pages, 10 figures