Stochastic gravitational-wave background in quantum gravity

TL;DR

This paper evaluates various quantum gravity models for their potential to produce a detectable stochastic gravitational-wave background, finding that only some blue-tilted models could be observed by future detectors like DECIGO.

Contribution

It systematically compares five quantum gravity-inspired scenarios for their gravitational-wave signatures and assesses their detectability with current and future interferometers.

Findings

Non-local quantum gravity is undetectable.

Most models can reach DECIGO sensitivity.

Models with red-tilted spectra are non-detectable.

Abstract

Among all cosmological quantum-gravity or quantum-gravity-inspired scenarios, only very few predict a blue-tilted primordial tensor spectrum. We explore five of them and check whether they can generate a stochastic gravitational-wave background detectable by present and future interferometers: non-local quantum gravity, string-gas cosmology, new ekpyrotic scenario, Brandenberger-Ho non-commutative inflation and multi-fractional spacetimes. We show that non-local quantum gravity is unobservable, while all the other models can reach the strain sensitivity of DECIGO but not that of LIGO-Virgo-KAGRA, LISA or Einstein Telescope. Other quantum-gravity models with red-tilted spectra (most loop quantum cosmologies) or with exceptionally tiny quantum corrections (Wheeler-DeWitt quantum cosmology) are found to be non-detectable.