Gravitational Black Hole Hair from Event Horizon Supertranslations

TL;DR

The paper identifies a horizon-specific quotient of BMS symmetries, A ≡ BMS^H/BMS^-, whose generators induce intrinsic, gapless Bogoliubov modes on the Schwarzschild horizon. These A-modes function as black hole hair at the classical level, remaining ADM-mass invariant, while quantum effects lift their degeneracy to a finite set of N modes, yielding entropy that scales with N consistent with Bekenstein bounds. The authors connect these horizon Goldstone/Bogoliubov modes to quantum criticality, arguing that entropy counting emerges from a finite, N-dependent number of information carriers rather than a naive Planck-area pixel picture. They further relate the horizon-based hair to Minkowski vacua and gravitational scattering via IR structure and soft theorems, offering a unified geometric-quantum picture of black hole microstates and information flow. The framework is presented as extensible to arbitrary space-times with horizons, providing a concrete route to resolve the information puzzle through horizon symmetries and quantum criticality.

Abstract

We discuss BMS supertranslations both at null-infinity and on the horizon for the case of the Schwarzschild black hole. We show that both kinds of supertranslations lead to infinetly many gapless physical excitations. On this basis we construct a quotient algebra using suited superpositions of both kinds of transformations which cannot be compensated by an ordinary BMS-supertranslation and therefore are intrinsically due to the presence of an event horizon. We show that these quotient transformations are physical and generate gapless excitations on the horizon that can account for the gravitational hair as well as for the black hole entropy. We identify the physics of these modes as associated with Bogolioubov-Goldstone modes due to quantum criticality. Classically the number of these gapless modes is infinite. However, we show that due to quantum criticality the actual amount of information-carriers becomes finite and consistent with Bekenstein entropy. Although we only consider the case of Schwarzschild geometry, the arguments are extendable to arbitrary space-times containing event horizons.