Superradiant Axionic Black-Hole Clouds as Seeds for Graviton Squeezing
Abstract
It is shown that both, standard general relativity (GR) and Chern-Simons (CS) gravity, the latter containing chiral gravitational anomaly terms, seed the production of pairs of entangled gravitons in a multi-mode squeezed state. This involves the interaction of gravitons with the axionic cloud surrounding a superradiant Kerr (rotating) black hole background. The order of magnitude of the squeezing effect, specifically the number of graviton excitations in the squeezed vacuum, is estimated in the non-relativistic limit, relevant for the superradiance process. It is found analytically that the squeezing from the GR process of annihilation of two axions into two gravitons, dominates, by many orders of magnitude, that coming from the axion decay into two gravitons, induced by the higher-derivative CS term. It is also shown that significant squeezing effects are produced in the case of long-lived axionic clouds, whose lifetimes are much longer than the timescale for which superradiance is effective. A brief discussion on current exclusion (for the first time) of very-long axion-cloud lifetimes, through comparison of our results with current LIGO data, as well as potential detection of such effects in future interferometers is also given
Cite
@article{arxiv.2507.01689,
title = {Superradiant Axionic Black-Hole Clouds as Seeds for Graviton Squeezing},
author = {Panagiotis Dorlis and Nick E. Mavromatos and Sarben Sarkar and Sotirios-Neilos Vlachos},
journal= {arXiv preprint arXiv:2507.01689},
year = {2025}
}
Comments
8 pages revtex, four pdf figures incorporated. Discussion and references on observational prospects added. Version matches that published in Physical Review Letters