Warped entanglement entropy

We study the applicability of the covariant holographic entanglement entropy proposal to asymptotically warped AdS(3) spacetimes with an SL(2, R) x U(1) isometry. We begin by applying the proposal to locally AdS(3) backgrounds which are written as an R-1 fibration over AdS(2). We then perturb away from this geometry by considering a warping parameter a = 1 + delta to get an asymptotically warped AdS(3) spacetime and compute the dual entanglement entropy perturbatively in delta. We find that for large separation in the fiber coordinate, the entanglement entropy can be computed to all orders in delta and takes the universal form appropriate for two-dimensional CFTs. The warping-dependent central charge thus identified exactly agrees with previous calculations in the literature. Performing the same perturbative calculations for the warped BTZ black hole again gives universal two-dimensional CFT answers, with the left-moving and right-moving temperatures appearing appropriately in the result.