Echoes from beyond: Detecting gravitational-wave quantum imprints with LISA

TL;DR

This paper explores the potential for LISA to detect gravitational wave echoes caused by quantum effects at black hole horizons, offering a novel way to probe quantum gravity and black hole entropy.

Contribution

It introduces a new phenomenological model for black hole reflectivity based on Bekenstein's quantization, and assesses the detectability of echoes with LISA.

Findings

LISA can potentially detect quantum gravitational echoes.

Detection of echoes can directly probe Bekenstein-Hawking entropy.

LISA data can constrain various quantum gravity theories.

Abstract

We assess the prospects for detecting gravitational wave echoes arising due to the quantum nature of black hole horizons with LISA. In a recent proposal, Bekenstein's black hole area quantization is connected to a discrete absorption spectrum for black holes in the context of gravitational radiation. Consequently, for incoming radiation at the black hole horizon, not all frequencies are absorbed, raising the possibility that the unabsorbed radiation is reflected, producing an echo-like signal closely following the binary coalescence waveform. In this work, we further develop this proposal by introducing a robust, phenomenologically motivated model for black hole reflectivity. Using this model, we calculate the resulting echoes for an ensemble of Numerical Relativity waveforms and examine their detectability with the LISA space-based interferometer. Our analysis demonstrates promising detection prospects and shows that, upon detection, LISA provides a direct probe of the Bekenstein-Hawking entropy. In addition, we find that the information extractable from LISA data offers valuable constraints on a wide range of quantum gravity theories.