Gravitational Memory Effect for Near-Horizon Asymptotic Symmetries

Abstract

Gravitational memory effect has emerged as a new window and opened up several intriguing avenues in the field of gravitational wave astronomy together with its inter-connection to asymptotic symmetries (AS). The recent developments in this direction have drawn considerable attention from theoretical as well as observational perspectives. It has been shown that such effects can also be recovered near the horizon of black holes which might play a crucial role in understanding the information paradox. With this motivation, we have studied the gravitational memory effect near the horizon of black holes analogous to the one obtained at asymptotic null infinity. We first study how the AS emerge near the horizon of black holes and how they can be detected via some ideal detectors as some permanent change of configurations (Memory) once GW passes through the setup. The emergence of AS is studied from two different perspectives. First, how AS emerge as soldering freedoms when two black holes are being glued along a common null surface. Secondly, in the form of AS that preserve the asymptotic form of the near horizon metric of a black hole. We have established an analogous form of the displacement memory near the horizon of non-extreme and extreme black holes for both these perspectives. We also discuss the detection prospects of the supertranslation memory or hair. In this direction, other than the memory effect, we have explored the possibility of detecting a supertranslated black hole through standard tests of General Relativity. We propose a scenario in which such a configuration may be distinguished from ordinary black holes by examining the photon trajectories near the horizon. As we know that the gravitational memory has not been detected yet, in this direction, our study might serve as a useful contribution towards investigation of the signatures of AS in the future.