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Abstract |
We present a cosmological reassessment of light sterile-neutrino scenarios, examining whether current observations exclude sterile neutrinos as a class or primarily constrain the fully thermalized case. We consider three distinct realizations; (i) a fully thermalized sterile (FTS) species, (ii) a different-temperature sterile-neutrino thermal relic (DTS) relative to the active neutrino background and (iii) a Dodelson-Widrow-like (DW) sterile neutrino with reduced phase-space normalization. Constraints are derived within both ACDM and the CPL dynamical dark-energy framework using combinations of Planck-Cosmic Microwave Background data, DESI DR2 BAO measurements, and the PantheonPlus and Union3 Type Ia supernova samples. For baseline data combinations without a local H0 prior, the FTS scenario is strongly disfavored in both cosmological models. Adding the local HDN0 prior allows ACDM & thorn; FTS to accommodate the high local H0 value and become statistically competitive with standard ACDM once SNIa data are included, although the sterile-neutrino mass remains consistent with zero. By contrast, partially populated sterile-neutrino scenarios remain viable: the DW realization is broadly compatible with current observations, while the DTS scenario yields the least cosmological pressure among the cases considered. Overall, cosmological data mainly require a strongly suppressed effective sterile abundance, leading to tight constraints on meff s while allowing substantially weaker bounds on the physical sterile mass. We conclude that current observations do not generically exclude sterile neutrinos, but rather place strong pressure on fully thermalized or highly populated scenarios, highlighting the importance of production history and phase-space distribution when interpreting cosmological constraints. |
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Address |
[Ladeira, Artur; Nunes, Rafael C.] Univ Fed Rio Grande do Sul, Inst Fis, BR-91501970 Porto Alegre, RS, Brazil; [Nunes, Rafael C.] Inst Nacl Pesquisas Espaciais, Div Astrofis, Ave Astronautas 1758, BR-12227010 Sao Jose Dos Campos, SP, Brazil; [Di Valentino, Eleonora] Univ Sheffield, Sch Math & Phys Sci, Hounsfield Rd, Sheffield S3 7RH, England; [Gariazzo, Stefano] Univ Valencia, Inst Fis Corpuscular IFIC, CSIC, Valencia, Spain; [Gariazzo, Stefano] Univ Turin, Phys Dept, Via P Giuria 1, I-10125 Turin, Italy; [Gariazzo, Stefano] INFN, Sez Torino, Via P Giuria 1, I-10125 Turin, Italy, Email: artur.ladeira@ufrgs.br; |
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