  We search for the presence of cosmological neutrino background (CNB)
anisotropies in recent WMAP 5-year data using their signature imprinted on
modifications to cosmic microwave background (CMB) anisotropy power spectrum.
By parametrizing the neutrino background anisotropies with the speed viscosity
parameter $c_\vis$, we find that the WMAP 5-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, 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 ansiotropies and other cosmological para meters such as the number
of effective neutrinos species and the dark energy equation of state.
