Relic gravitational waves from primordial gravitational collapses
Abstract
A large primordial density perturbation of the Hubble scale will gravitationally collapse, generating an outgoing sound shell, whether or not a primordial black hole (PBH) is formed. In this Letter, we report a hybrid numerical analysis of the stochastic gravitational wave background induced by the collision of sound shells in the early Universe. The peak frequency and amplitude in the GW spectrum depend on the Hubble horizon and the abundance of sound shells. Abundant density perturbations would lead to GW backgrounds potentially detectable for future pulsar timing arrays and ground-based/space-borne detectors. For those perturbations that collapse into PBHs, future null detection of the corresponding high-frequency GW background could put new observational constraints on those PBHs that have already evaporated.
Keywords
Cite
@article{arxiv.2504.11275,
title = {Relic gravitational waves from primordial gravitational collapses},
author = {Xiang-Xi Zeng and Zhuan Ning and Zi-Yan Yuwen and Shao-Jiang Wang and Heling Deng and Rong-Gen Cai},
journal= {arXiv preprint arXiv:2504.11275},
year = {2026}
}
Comments
v3, 5 pages + 7 pages, 3 figures, largely extended supplemental materials with 4 figures, two accompanying papers 2504.12243 (numerical GR simulations for sound waves) and 2512.21151 (improved GR simulations for sound waves + hydrodynamic simulation confirmations for sound-shell collisions) are referred to