Anisotropies in the cosmic neutrino background after Wilkinson Microwave Anisotropy Probe five-year data

We search for the presence of cosmological neutrino background ( CNB) anisotropies in recent Wilkinson Microwave Anisotropy Probe ( WMAP) five-year data using their signature imprinted on modi. cations to the cosmic microwave background ( CMB) anisotropy power spectrum. By parameterizing the neutrino background anisotropies with the speed viscosity parameter c(vis), we find that the WMAP five-year data alone provide only a weak indication for CNB anisotropies with c(vis)(2) > 0.06 at the 95% confidence level. When we combine CMB anisotropy data with measurements of galaxy clustering, the SN-Ia Hubble diagram, and other cosmological information, the detection increases to c(vis)(2) > 0.16 at the same 95% confidence level. Future data from Planck, combined with a weak lensing survey such as the one expected with DUNE from space, will be able to measure the CNB anisotropy parameter at about 10% accuracy. We discuss the degeneracy between neutrino background anisotropies and other cosmological parameters such as the number of effective neutrinos species and the dark energy equation of state.