English

Seesaw Cosmology

High Energy Physics - Phenomenology 2026-07-29 v1 Cosmology and Nongalactic Astrophysics

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 seesawseesaw cosmologycosmology. 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 a1/4a^{-1/4} and a3/8a^{-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)m_\phi/(2m_N), while ultraviolet freeze-in exhibits the critical temperature powers p=12p = 12 and 2020, 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.

Cite

@article{arxiv.2607.27325,
  title  = {Seesaw Cosmology},
  author = {Nicolás Bernal and Chee Sheng Fong and Óscar Zapata},
  journal= {arXiv preprint arXiv:2607.27325},
  year   = {2026}
}

Comments

16+4 pages, 3 figures