Neutrino and dark radiation properties in light of recent CMB observations

Abstract

Recent cosmic microwave background measurements at high multipoles from the South Pole Telescope and from the Atacama Cosmology Telescope seem to disagree in their conclusions for the neutrino and dark radiation properties. In this paper we set new bounds on the dark radiation and neutrino properties in different cosmological scenarios combining the ACT and SPT data with the nine-year data release of the Wilkinson Microwave Anisotropy Probe (WMAP-9), baryon acoustic oscillation data, Hubble Telescope measurements of the Hubble constant, and supernovae Ia luminosity distance data. In the standard three massive neutrino case, the two high multipole probes give similar results if baryon acoustic oscillation data are removed from the analyses and Hubble Telescope measurements are also exploited. A similar result is obtained within a standard cosmology with N eff massless neutrinos, although in this case the agreement between these two measurements is also improved when considering simultaneously baryon acoustic oscillation data and Hubble Space Telescope measurements. In the N eff massive neutrino case the two high multipole probes give very different results regardless of the external data sets used in the combined analyses. When considering extended cosmological scenarios with a dark energy equation of state or with a running of the scalar spectral index, the evidence for neutrino masses found for the South Pole Telescope in the three neutrino scenario disappears for all the data combinations explored here. Again, adding Hubble Telescope data seems to improve the agreement between the two high multipole cosmic microwave background measurements considered here. In the case in which a dark radiation background with unknown clustering properties is also considered, SPT data seem to exclude the standard value for the dark radiation viscosity c 2 vis ¼ 1=3 at the 2 C.L., finding evidence for massive neutrinos only when combining SPT data with baryon acoustic oscillation measurements.

Dark radiation constraints on minicharged particles in models with a hidden photon

“…The obtained values tended to be larger than 3, raising the excitement of a possible hint of new physics, see e.g. [71][72][73]. The latest CMB results of WMAP, SPT [74] and ACT [75] combined with BAO and HST gave N eff = 3.84 ± 0.40 at 68% C.L.…”

Constraints on dark matter annihilation from CMB observations before Planck

“…In this work, we compute the constraints from these recent CMB measurements on annihilating DM particles with masses ranging from 1 MeV to 1 TeV, in combination with Baryon Acoustic Oscillation (BAO) data and Hubble Space Telescope (HST) measurements of the Hubble constant. Since ACT and SPT high multipole CMB measurements seem to disagree on the value of several cosmological parameters such as the effective number of relativistic species, the lensing potential, the neutrino masses and the properties of the dark radiation background [35][36][37], we analyze these two data sets separately.…”

Robustness of cosmic neutrino background detection in the cosmic microwave background

“…The strategy of several recent papers [20][21][22][23][24] was to introduce 2 two phenomenological parameters, c eff and c vis . The effect of the parameter c 2 eff is to generalize the linear relation between isotropic pressure perturbations and density perturbations, while c 2 vis directly modifies the anisotropic stress equation for neutrinos.…”