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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.
Bernardis et al. (Tue,) studied this question.