Neutrino Physics in the Light of WMAP

Abstract

We investigate the implications of recent cosmic microwave background radiation (CMB) and large scale structure (LSS) results the neutrino background and mass. We use the recent WMAP data, together with previous CBI data and 2dF matter power spectrum, to constrain the effective number of neutrino species N eff and the neutrino mass in a general Cosmology. We find that N eff=4.08 with a 95 per cent C.L. 1.9≤N eff≤6.62. The curvature we derive is still consistent with flat, but assuming a flat Universe from the beginning implies a bias toward lower N eff, as well as artificially smaller error bars. We analyze and discuss the degeneracies with other parameters, and point out that probes of the matter power spectrum on smaller scales, accurate independent σ8 measurements, together with better independent measurement of H 0 would help in breaking the degeneracies. As for the neutrino mass, we show that CMB and matter power spectrum at the present time are unable to constrain the neutrino mass below 0.4 eV, unless a strong assumption on the bias parameter is assumed. Adding constraints on σ8 significantly reduces the uncertainty on the neutrino mass.