Dynamical effects of the neutrino gravitational clustering at Planck angular scales

Abstract

We study the cosmic microwave background (CMB) anisotropy induced by the nonlinear perturbations in the massive neutrino density associated with the nonlinear gravitational clustering process. By using N-body simulations, we compute the imprint left by gravitational clustering on the CMB anisotropy power spectrum for all nonlinear scales, taking into account the time evolution of all nonlinear density perturbations, for a flat, cold, hot dark matter model with cosmological constant (ACHDM) consistent with large-scale structure data and the latest CMB measurements with different neutrino fractions fcorresponding to a neutrino total mass in the range allowed by the neutrino oscillation and double beta decay experiments. We find that the nonlinear time-varying potential induced by the gravitational clustering process generates metric perturba- tions, leading to a decrease in the CMB anisotropy power spectrum of amplitude DT=T � 10 � 6 for angular resolutions between � 4 0 and 20 0 , depending on the cluster mass scale and the neutrino fraction f� . We find a better consistency between the CMB angular power spectrum derived from BOOMERANG data and that derived from MAXIMA-1 and DASI and a slight reduction of the errors on most of the cosmological param- eters when the nonlinear effects induced by the gravitational clustering are taken into account. Our results show that, for a neutrino fraction in agreement with that indicated by astroparticle and nuclear physics experiments, and a cosmological accreting mass comparable with the mass of known clusters, the angular res- olution and sensitivity of the CMB anisotropy measurements from the Planck satellite will allow the detec- tion of the dynamical effects of gravitational clustering. In addition, including the nonlinear aspects of the neutrino gravitational clustering allows reduction in the errors on ns and � . This work has been performed within the framework of the Planck LFI activities. Subject headings: cosmic microwave background — dark matter — elementary particles — large-scale structure of universe