Constraints on massive sterile plus active neutrino species in non minimal cosmologies

TL;DR

This work assesses how non-minimal cosmological models alter cosmological bounds on active and sterile neutrinos. Using Bayesian MCMC analyses with CAMB/CosmoMC and diverse datasets, it explores $w$CDM, $w(a)$CDM, $\,Omega_k$CDM, and xiCDM scenarios to constrain $m_ u$, $m_{ u_s}$, and $N_{ u_s}$. The key finding is that $(3+2)$ sterile neutrino configurations with masses around $0.5$ eV remain viable at 95% CL in several non-minimal cosmologies, though BBN constraints can tighten if the sterile states are fully thermalized; degeneracies with dark energy and curvature can partly obscure these limits. These results support the possibility that sterile neutrinos can coexist with cosmology and may help reconcile short-baseline anomalies with cosmological data, especially in light of updated reactor flux predictions.

Abstract

Cosmological measurements are affected by the energy density of both active and sterile massive neutrinos. We extend here a recent analysis of current cosmological data to non minimal cosmologies. Several possible scenarios are examined: a constant w \neq -1 dark energy equation of state, a non flat universe, a time varying dark energy component and coupled dark matter dark energy universes or modified gravity scenarios. When considering cosmological data only, (3+2) massive neutrino models with ~0.5 eV sterile species are allowed at 95% CL. This scenario has been shown to reconcile reactor, LSND and MiniBooNE positive signals with null results from other searches. Big Bang Nucleosynthesis bounds could compromise the viability of (3+2) models if the two sterile species are fully thermalized states at decoupling.

Figures (5)

• Figure 1: The upper panel shows the 68% and 95% CL bounds from "run 1" in the plane $w-m_{\nu}$ (in blue) and $w$-$m_{{\nu}_s}$ (in red), respectively. The masses of the sterile and active neutrinos are both in eV. The lower panel depicts the 68% and 95% CL contours in the plane $w-N_{{\nu}_s}$ for a constant dark energy equation of state.
• Figure 2: 68% and 95% CL contours arising from "run 1" in the plane $w-N_{{\nu}_s}$ for the $w(a)$CDM cosmology.
• Figure 3: The upper panel shows the 68% and 95% CL bounds from "run 1" in the $\Omega_k-N_{{\nu}_s}$ plane. The lower plane shows the analogous in the $\Omega_k-m_{\nu}$ (in blue) and $\Omega_k-m_{{\nu}_s}$ (in red) planes, respectively. The masses of the sterile and active neutrinos are both in eV.
• Figure 4: 68% and 95% CL bounds arising from the "run 1" analysis in the plane $\xi-N_{\nu_s}$ for a universe with an interacting dark matter-dark energy fluid.
• Figure 5: The upper panel shows the 68% and 95% CL bounds from "run 1" in the $m_\nu-N_{{\nu}_s}$ plane. The lower plane shows the analogous in the $N_{{\nu}_s}-m_{{\nu}_s}$ plane. The masses of the sterile and active neutrinos are both in eV. Red, blue, magenta and green contours denote $w$CDM, $w(a)$CDM, $\Omega_k$CDM and $\xi$CDM cosmologies, respectively.