Seesaw Cosmology
Abstract
We study perturbative reheating in which the inflaton transfers its energy to the Standard Model through right-handed neutrinos (RHNs) responsible for light-neutrino masses via the type-I seesaw mechanism. We refer to the resulting nonstandard thermal history as seesaw $cosmology$. When produced relativistically and sufficiently long lived, the RHNs generate a characteristic sequence of inflaton, relativistic-RHN, nonrelativistic-RHN, and Standard Model radiation domination. We solve the Boltzmann system while retaining the production-time dependence of the nonthermal RHN distribution and its relativistic-to-nonrelativistic transition. The Standard Model temperature rapidly approaches a plateau during inflaton domination and subsequently scales as a−1/4 and a−3/8 during relativistic- and nonrelativistic-RHN domination, respectively. We investigate the implications of seesaw cosmology for dark-matter production. Direct production through inflaton decays can be enhanced relative to conventional reheating by a factor of order mϕ/(2mN), while ultraviolet freeze-in exhibits the critical temperature powers p = 12 and $20$, leading to potentially large contributions before the final radiation-dominated era. Seesaw cosmology therefore connects neutrino-mass generation, the pre-BBN thermal history and phenomena such as dark-matter production and baryogenesis.
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BibTeX
@misc{bernal2026seesaw,
title = {{Seesaw Cosmology}},
author = {Nicolás Bernal and Chee Sheng Fong and Óscar Zapata},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2607.27325},
eprint = {2607.27325},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2607.27325},
}
RIS
TY - UNPB
TI - Seesaw Cosmology
AU - Nicolás Bernal
AU - Chee Sheng Fong
AU - Óscar Zapata
PY - 2026
DA - 2026/10/21
PB - arXiv
DO - 10.48550/arxiv.2607.27325
UR - https://arxiv.org/abs/2607.27325
AB - We study perturbative reheating in which the inflaton transfers its energy to the Standard Model through right-handed neutrinos (RHNs) responsible for light-neutrino masses via the type-I seesaw mechanism. We refer to the resulting nonstandard thermal history as seesaw $cosmology$. When produced relativistically and sufficiently long lived, the RHNs generate a characteristic sequence of inflaton, relativistic-RHN, nonrelativistic-RHN, and Standard Model radiation domination. We solve the Boltzmann system while retaining the production-time dependence of the nonthermal RHN distribution and its relativistic-to-nonrelativistic transition. The Standard Model temperature rapidly approaches a plateau during inflaton domination and subsequently scales as a^−1/4 and a^−3/8 during relativistic- and nonrelativistic-RHN domination, respectively. We investigate the implications of seesaw cosmology for dark-matter production. Direct production through inflaton decays can be enhanced relative to conventional reheating by a factor of order m_ϕ/(2m_N), while ultraviolet freeze-in exhibits the critical temperature powers p = 12 and $20$, leading to potentially large contributions before the final radiation-dominated era. Seesaw cosmology therefore connects neutrino-mass generation, the pre-BBN thermal history and phenomena such as dark-matter production and baryogenesis.
ER -