Cosmology seeking friendship with sterile neutrinos

Abstract

Precision cosmology and big-bang nucleosynthesis mildly favor extra radiation in the universe beyond photons and ordinary neutrinos, lending support to the existence of low-mass sterile neutrinos. We use the WMAP 7-year data, small-scale CMB observations from ACBAR, BICEP and QuAD, the SDSS 7th data release, and measurement of the Hubble parameter from HST observations to derive credible regions for the assumed common mass scale m_s and effective number N_s of thermally excited sterile neutrino states. Our results are compatible with the existence of one or perhaps two sterile neutrinos, as suggested by LSND and MiniBooNE, if m_s is in the sub-eV range.

Figures (1)

• Figure 1: 2D marginalized 68%, 95% and 99% credible regions for the neutrino mass and thermally excited number of degrees of freedom $N_{\rm s}$. Top: The $3+N_{\rm s}$ scheme, in which ordinary neutrinos have $m_\nu=0$, while sterile states have a common mass scale $m_{\rm s}$. Bottom: The $N_{\rm s}+3$ scheme, where the sterile states are taken to be massless $m_{\rm s}=0$, and 3.046 species of ordinary neutrinos have a common mass $m_\nu$.