Cosmological Consequences of a Highly Decoupled Right-handed Neutrino
Abstract
In the minimal type-I seesaw, one right-handed neutrino (RHN) can decouple from neutrino mass generation. Such a state is usually neglected, yet its feeble couplings make it long-lived, and it can dominate the energy density of the Universe before decaying. We study this in a minimal U(1)B−L model, where the RHNs are produced through B−L gauge interactions, for the cases of a decoupled lightest RHN N1 and a decoupled heaviest RHN N3. The resulting early matter-dominated era dilutes the baryon asymmetry, and for decoupled N3 it also delays the equilibration of the charged-lepton Yukawa interactions, allowing a lighter N1 to generate the asymmetry in the unflavoured regime. Breaking U(1)B−L forms cosmic strings whose gravitational-wave background acquires a spectral break from the early matter-dominated era, with a frequency set by the decoupled RHN mass and the lightest neutrino mass, within reach of future detectors such as SKA, THEIA, LISA, μARES, DECIGO and ET.
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BibTeX
@misc{king2026cosmological,
title = {{Cosmological Consequences of a Highly Decoupled Right-handed Neutrino}},
author = {Stephen F. King and Rishav Roshan and Sudipta Show},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.18334},
eprint = {2610.18334},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.18334},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Cosmological Consequences of a Highly Decoupled Right-handed Neutrino
AU - Stephen F. King
AU - Rishav Roshan
AU - Sudipta Show
PY - 2026
DA - 2026/10/13
PB - arXiv
DO - 10.48550/arxiv.2610.18334
UR - https://arxiv.org/abs/2610.18334
AB - In the minimal type-I seesaw, one right-handed neutrino (RHN) can decouple from neutrino mass generation. Such a state is usually neglected, yet its feeble couplings make it long-lived, and it can dominate the energy density of the Universe before decaying. We study this in a minimal U(1)_B−L model, where the RHNs are produced through B−L gauge interactions, for the cases of a decoupled lightest RHN N_1 and a decoupled heaviest RHN N_3. The resulting early matter-dominated era dilutes the baryon asymmetry, and for decoupled N_3 it also delays the equilibration of the charged-lepton Yukawa interactions, allowing a lighter N_1 to generate the asymmetry in the unflavoured regime. Breaking U(1)_B−L forms cosmic strings whose gravitational-wave background acquires a spectral break from the early matter-dominated era, with a frequency set by the decoupled RHN mass and the lightest neutrino mass, within reach of future detectors such as SKA, THEIA, LISA, μARES, DECIGO and ET.
ER -