  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.
