Thermalization of the Primordial Stochastic Gravitational-Wave Background
Abstract
It is conventionally believed that the Stochastic Gravitational-Wave Background (SGWB) from inflation provides information about the earliest universe. However, in this Letter, we present a different picture. Our analysis starts from the observation that the inflation-predicted spectrum implies gravitons reside in high-occupation states, which significantly enhances their self-interactions and triggers rapid thermalization. We show that approximately 80% of the primordial gravitons participate in this thermalization, forming a Bose--Einstein distribution and thereby erasing the primordial information. Evaluated using typical inflation parameters, this thermalized spectrum yields a present-day peak frequency of f0, peak(th) ∼ 1.4 × 108 Hz in the hundred-megahertz band with a peak amplitude of Ω0, peak(th) ∼ 3.5 × 10−13. Due to the sharp drop-off away from the peak, the resulting spectrum lies beyond the reach of low-frequency observatories like PTAs, LISA, and LIGO, but remains uniquely accessible to high-frequency detectors such as microwave cavity resonators and dielectric haloscopes.
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BibTeX
@misc{zhang2026thermalization,
title = {{Thermalization of the Primordial Stochastic Gravitational-Wave Background}},
author = {Hongguang Zhang and Zhengyang Qiu and Sirui Wang and Jiayi Wei},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.20325},
eprint = {2610.20325},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.20325},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Thermalization of the Primordial Stochastic Gravitational-Wave Background
AU - Hongguang Zhang
AU - Zhengyang Qiu
AU - Sirui Wang
AU - Jiayi Wei
PY - 2026
DA - 2026/10/14
PB - arXiv
DO - 10.48550/arxiv.2610.20325
UR - https://arxiv.org/abs/2610.20325
AB - It is conventionally believed that the Stochastic Gravitational-Wave Background (SGWB) from inflation provides information about the earliest universe. However, in this Letter, we present a different picture. Our analysis starts from the observation that the inflation-predicted spectrum implies gravitons reside in high-occupation states, which significantly enhances their self-interactions and triggers rapid thermalization. We show that approximately 80% of the primordial gravitons participate in this thermalization, forming a Bose--Einstein distribution and thereby erasing the primordial information. Evaluated using typical inflation parameters, this thermalized spectrum yields a present-day peak frequency of f_0, peak^(th) ∼ 1.4 × 10^8 Hz in the hundred-megahertz band with a peak amplitude of Ω_0, peak^(th) ∼ 3.5 × 10^−13. Due to the sharp drop-off away from the peak, the resulting spectrum lies beyond the reach of low-frequency observatories like PTAs, LISA, and LIGO, but remains uniquely accessible to high-frequency detectors such as microwave cavity resonators and dielectric haloscopes.
ER -