Reactor sterile neutrinos, dark energy and the age of the universe

TL;DR

The paper investigates whether two light sterile neutrinos, motivated by reactor oscillation data, can be accommodated in cosmology and what this implies for dark energy. It uses CosmoMC to compare LambdaCDM and wCDM+k with 0/1/2 sterile species, adopting fully thermalized masses from reactor fits ($m_{nu_s}=1.33$ eV for 1 nu_s and $m_{nu_s}^{(1)}=0.68$ eV, $m_{nu_s}^{(2)}=0.94$ eV for 2 nu_s). The results show that two sterile neutrinos reduce the inferred age to about 12.6–12.8 Gyr and lower the dark-energy density, with LambdaCDM fitting worse than the sterile-free case, while allowing curvature and a varying equation of state yields $w$ values below -1 and mitigates the chi-square penalty. This indicates a potential tension between a cosmological constant and sterile-neutrino scenarios, highlighting the need for flexible dark energy models should the oscillation hints be confirmed.

Abstract

There are indications that the neutrino oscillation data from reactor experiments and the LSND and MiniBooNE experiments show a preference for two sterile neutrino species, both with masses in the eV region. We show that this result has a significant impact on some important cosmological parameters. Specifically, we use a combination of CMB, LSS and SN1A data and show that the existence of two light, sterile neutrinos would rule out the cosmological constant as dark energy at 95% confidence level, and lower the expansion age of the universe to 12.58 \pm 0.26 Gyr.

Figures (3)

• Figure 1: Marginalized parameter distributions for $\Lambda$CDM with and without additional sterile neutrinos. Solid, red lines: No sterile neutrinos. Dashed, blue lines: 1 sterile neutrino. Dotted, black lines: 2 sterile neutrinos. Thin lines show results from using WMAP7 data only. Results from WMAP7++ are shown with thick lines.
• Figure 2: Marginalized parameter distributions for wCDM+k with and without additional sterile neutrinos. Labels are the same as in Figure \ref{['fig:1D_LCDM']}. Since these models are very poorly constrained when using WMAP7 data only, we only show the results from WMAP7++.
• Figure 3: Marginalized 2D parameter distributions for wCDM+k with and without additional sterile neutrinos. Labels are the same as in Figure \ref{['fig:1D_LCDM']}. Since these models are very poorly constrained when using WMAP7 data only, we only show the results from WMAP7++.