Quantum production of gravitational waves after inflation
Abstract
A variety of mechanisms in the early Universe lead to the generation of gravitational waves (GWs). We introduce here a novel source of GWs generated by vacuum fluctuations after inflation. Given that gravitons are minimally coupled particles, their quantum creation takes place during inflation, but is absent in an unperturbed Universe during the radiation-dominated epoch, since they behave as conformally coupled particles. However, the presence of inhomogeneities breaks the conformal flatness of the metric, allowing scalar metric perturbations to induce the quantum production of gravitons. We compute the resulting GW spectrum from this mechanism for different models of the primordial scalar power spectrum. We find that this GW signal peaks around the GHz frequency range, distinguishing it from other astrophysical and cosmological backgrounds and underscoring the need for detectors sensitive to these high frequencies.
Cite
@article{arxiv.2507.08737,
title = {Quantum production of gravitational waves after inflation},
author = {Alina Mierna and Gabriele Perna and Sabino Matarrese and Nicola Bartolo and Angelo Ricciardone},
journal= {arXiv preprint arXiv:2507.08737},
year = {2026}
}
Comments
8 pages + 1 figure