Robust neutrino constraints by combining low redshift observations with the CMB

We illustrate how recently improved low-redshift cosmological measurements can tighten constraints on neutrino properties. In particular we examine the impact of the assumed cosmological model on the constraints. We first consider the new HST H 0 = 74.2±3.6 measurement by Riess et al. (2009) and the σ 8 (Ω m /0.25) 0.41 = 0.832±0.033 constraint from Rozo et al. (2009) derived from the SDSS maxBCG Cluster Catalog. In a ΛCDM model and when combined with WMAP5 constraints, these low-redshift measurements constrain ∑ m ν < 0.4 eV at the 95% confidence level. This bound does not relax when allowing for the running of the spectral index or for primordial tensor perturbations. When adding also Supernovae and BAO constraints, we obtain a 95% upper limit of ∑ m ν < 0.3eV. We test the sensitivity of the neutrino mass constraint to the assumed expansion history by both allowing a dark energy equation of state parameter w ≠−1 and by studying a model with coupling between dark energy and dark matter, which allows for variation in w , Ω k , and dark coupling strength ξ. When combining CMB, H 0 and the SDSS LRG halo power spectrum from Reid et al. 2009, we find that in this very general model, ∑ m ν < 0.51 eV with 95% confidence. If we allow the number of relativistic species N rel to vary in a ΛCDM model with ∑ m ν = 0, we find N rel = 3.76 +0.63 −0.68 ( +1.38 −1.21 ) for the 68% and 95% confidence intervals. We also report prior-independent constraints, which are in excellent agreement with the Bayesian constraints.