Gadelha, A. L.Marchioro, Dafni Z.Nedel, Daniel L.2014-05-202014-05-202006-08-10Physics Letters B. Amsterdam: Elsevier B.V., v. 639, n. 3-4, p. 383-388, 2006.0370-2693http://hdl.handle.net/11449/23302In this Letter new aspects of string theory propagating in a pp-wave time dependent background with a null singularity are explored. It is shown the appearance of a 2d entanglement entropy dynamically generated by the background. For asymptotically flat observers, the vacuum close to the singularity is unitarily inequivalent to the vacuum at tau = -infinity and it is shown that the 2d entanglement entropy diverges close to this point. As a consequence. The positive time region is inaccessible for observers in tau = -infinity. For a stationary measure, the vacuum at finite time is seen by those observers as a thermal state and the information loss is encoded as a heat bath of string states. (c) 2006 Elsevier B.V. All rights reserved.383-388engArtigo10.1016/j.physletb.2006.06.044WOS:000239676500039Acesso restrito