In this paper, we study the collapse of a massive shell in 2+1 and 3+1 dimensional gravity with anti-de Sitter asymptotics. Using the Gauss-Codazzi method, we derive gravitational equations of motion of the shell. We then use the functional Schrödinger formalism to calculate the spectrum of particles produced during the collapse. At the late time, radiation agrees very well with the standard Hawking results. In 3+1 dimensions, we reproduce the Hawking-Page transition. We then construct the density matrix of this collapsing system and analyze the information content in the emitted radiation. We find that the off-diagonal elements of the density matrix are very important in preserving the unitarity of the system.
Saini, A., & Stojkovic, D. (2018). Gravitational collapse and Hawking-like radiation of a shell in AdS spacetime. Physical Review D, 97(2). https://doi.org/10.1103/PhysRevD.97.025020