Partially Thermalized eV-Scale Sterile Neutrinos in Dynamical Dark Energy and Non-Flat Cosmologies
Abstract
We investigate cosmological constraints on a (3+1) neutrino framework containing an additional partially thermalized, eV-scale sterile neutrino alongside the three active species. Rather than assuming full thermalization, we allow the sterile abundance to vary independently through its physical mass ms and contribution ΔNeff to the effective number of relativistic species. The sterile state is modeled as a thermally distributed non-cold relic with a temperature below that of the active-neutrino background. We consider flat and non-flat ΛCDM and w0waCDM cosmologies, all including the same (3+1)ν sector. The models are constrained using Planck 2018 CMB data, DESI DR2 BAO, Pantheon+ Type Ia supernovae, a conservative compilation of fσ8 measurements, and the recent H0DN. Oscillation-informed priors are imposed on the active-neutrino mass splittings, while the eV scale sterile-mass range is motivated by short-baseline oscillation searches and global (3+1) analyses. We find that allowing additional freedom in the late-time cosmological background substantially changes the inferred sterile-neutrino sector. The effective sterile mass increases from ms,eff∼0.11±0.05 eV in flat ΛCDM+(3+1)ν to ∼0.35±0.12 eV in the non-flat w0waCDM+(3+1)ν model. The corresponding sterile abundance shifts from ΔNeff≲0.1 to ΔNeff≃0.35±0.15, while remaining well below the fully thermalized limit, ΔNeff≃1. The non-flat w0waCDM models also show ∼ 2.8σ preference for open spatial geometry, Ωk≃0.0045±0.0016, and yield H0≃70.9±0.7 km s−1 Mpc−1 and S8≃0.785±0.015. These models improve the minimum χ2 by approximately $21−25$ relative to flat ΛCDM+(3+1)ν.
Related
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- Probing eV-scale sterile neutrinos with neutrinoless double-beta decay and beta decay
- Sensitivities of Long and Medium Baseline Experiments to Sterile Neutrinos and Non-Standard Interactions
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BibTeX
@misc{kashyap2026partially,
title = {{Partially Thermalized eV-Scale Sterile Neutrinos in Dynamical Dark Energy and Non-Flat Cosmologies}},
author = {Gopal Kashyap and Kanhaiya Lal Pandey},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.10585},
eprint = {2610.10585},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.10585},
note = {CC BY-NC-SA 4.0},
}
RIS
TY - UNPB
TI - Partially Thermalized eV-Scale Sterile Neutrinos in Dynamical Dark Energy and Non-Flat Cosmologies
AU - Gopal Kashyap
AU - Kanhaiya Lal Pandey
PY - 2026
DA - 2026/10/06
PB - arXiv
DO - 10.48550/arxiv.2610.10585
UR - https://arxiv.org/abs/2610.10585
AB - We investigate cosmological constraints on a (3+1) neutrino framework containing an additional partially thermalized, eV-scale sterile neutrino alongside the three active species. Rather than assuming full thermalization, we allow the sterile abundance to vary independently through its physical mass m_s and contribution ΔN_eff to the effective number of relativistic species. The sterile state is modeled as a thermally distributed non-cold relic with a temperature below that of the active-neutrino background. We consider flat and non-flat ΛCDM and w_0w_aCDM cosmologies, all including the same (3+1)ν sector. The models are constrained using Planck 2018 CMB data, DESI DR2 BAO, Pantheon+ Type Ia supernovae, a conservative compilation of fσ_8 measurements, and the recent H0DN. Oscillation-informed priors are imposed on the active-neutrino mass splittings, while the eV scale sterile-mass range is motivated by short-baseline oscillation searches and global (3+1) analyses. We find that allowing additional freedom in the late-time cosmological background substantially changes the inferred sterile-neutrino sector. The effective sterile mass increases from m_s,eff∼0.11±0.05 eV in flat ΛCDM+(3+1)ν to ∼0.35±0.12 eV in the non-flat w_0w_aCDM+(3+1)ν model. The corresponding sterile abundance shifts from ΔN_eff≲0.1 to ΔN_eff≃0.35±0.15, while remaining well below the fully thermalized limit, ΔN_eff≃1. The non-flat w_0w_aCDM models also show ∼ 2.8σ preference for open spatial geometry, Ω_k≃0.0045±0.0016, and yield H_0≃70.9±0.7 km s^−1 Mpc^−1 and S_8≃0.785±0.015. These models improve the minimum χ^2 by approximately $21−25$ relative to flat ΛCDM+(3+1)ν.
ER -