Suppression of Gravitational-Wave Echoes in Diffeomorphism-Invariant Nonlocal Quantum Gravity

TL;DR

This paper explains why gravitational-wave echoes are suppressed in a specific nonlocal quantum gravity theory, showing that the suppression results from a covariant smearing effect that prevents the formation of echo cavities.

Contribution

It demonstrates that the absence of gravitational-wave echoes is due to a covariant nonlocal regulator smoothing out sharp structures, not from damping of frequencies.

Findings

Echo suppression is caused by a nonlocal regulator smoothing inner structures.

The mechanism applies to both black holes and horizonless objects.

Echo suppression is a structural consequence of nonlocality, not frequency damping.

Abstract

Searches for gravitational-wave echoes have been widely interpreted as probes of near-horizon structure and quantum modifications of black holes. We revisit the mechanism by which echoes are suppressed in a diffeomorphism-invariant, analytic entire-function ultraviolet completion of quantum gravity. We show that the absence of observable echoes is not due to a suppression of quasinormal-mode frequencies or a filtering of the gravitational-wave spectrum. The extreme blueshift of the proper local frequency in the near-horizon region activates the diffeomorphism-invariant entire-function regulator, which smooths out sharp reflecting inner structures and drives the reflection coefficient to zero. The nonlocal regulator acts as a covariant smearing operator on effective stress--energy and curvature, replacing sharp, partially reflective surfaces by smooth transition regions. As a result, the would-be echo cavity required for repeated reflections fails to form, and the associated phase-coherent back scattering is eliminated. This mechanism applies both to regular black holes with horizons and to horizonless compact objects generated by nonlocal smearing, and is independent of the detailed value of the nonlocal scale provided it lies at or above the Planck scale. Our results clarify the physical origin of echo suppression in nonlocal quantum gravity and demonstrate that the absence of echoes is a structural consequence of analytic nonlocality rather than a dynamical damping of gravitational-wave frequencies.