Superhorizon enhancement of the hydrodynamic GW tail in Standard Model embedded warm inflation
Abstract
Hydrodynamic fluctuations in the primordial plasma generate a gravitational-wave (GW) background that grows like f3scriptscriptstyle 0 in terms of the current frequency. However, within the (10−4 ... 104 )Hz band of upcoming interferometers, the modes likely re-entered the Hubble horizon when the hydrodynamic noise was no longer at its maximal value. To address this situation, we define a model-independent transfer function for GWs generated by hydrodynamic (or other white-noise) fluctuations at any time. Employing appropriate variables, we show how this transfer function, together with the simpler vacuum one, can be determined numerically for a general expansion history. The results are illustrated for Standard Model embedded warm inflation scenarios, including both the vacuum and hydrodynamic parts. Following previous estimates, we find that a pre-exit-generated hydrodynamic tail becomes almost flat below (105 ... 107 )Hz. Its small-f scriptscriptstyle 0 intercept remains finite, and can then moderately influence observational constraints through the tensor-to-scalar ratio (r).
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BibTeX
@misc{biondini2026superhorizon,
title = {{Superhorizon enhancement of the hydrodynamic GW tail in Standard Model embedded warm inflation}},
author = {Simone Biondini and M. Laine},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.19500},
eprint = {2610.19500},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.19500},
}
RIS
TY - UNPB
TI - Superhorizon enhancement of the hydrodynamic GW tail in Standard Model embedded warm inflation
AU - Simone Biondini
AU - M. Laine
PY - 2026
DA - 2026/10/14
PB - arXiv
DO - 10.48550/arxiv.2610.19500
UR - https://arxiv.org/abs/2610.19500
AB - Hydrodynamic fluctuations in the primordial plasma generate a gravitational-wave (GW) background that grows like f^3_scriptscriptstyle 0 in terms of the current frequency. However, within the (10^−4_ ... 10^4_ )Hz band of upcoming interferometers, the modes likely re-entered the Hubble horizon when the hydrodynamic noise was no longer at its maximal value. To address this situation, we define a model-independent transfer function for GWs generated by hydrodynamic (or other white-noise) fluctuations at any time. Employing appropriate variables, we show how this transfer function, together with the simpler vacuum one, can be determined numerically for a general expansion history. The results are illustrated for Standard Model embedded warm inflation scenarios, including both the vacuum and hydrodynamic parts. Following previous estimates, we find that a pre-exit-generated hydrodynamic tail becomes almost flat below (10^5_ ... 10^7_ )Hz. Its small-f^ _scriptscriptstyle 0 intercept remains finite, and can then moderately influence observational constraints through the tensor-to-scalar ratio (r).
ER -