Neutrino and Dark Radiation properties in light of latest CMB observations

TL;DR

This study analyzes recent CMB data to constrain neutrino and dark radiation properties, revealing discrepancies between measurements and highlighting the impact of different data combinations on cosmological parameter estimates.

Contribution

The paper provides new bounds on neutrino and dark radiation properties by combining multiple cosmological datasets, addressing inconsistencies between high multipole CMB measurements.

Findings

High multipole probes yield similar results without BAO and HST data in the three neutrino case.

Agreement improves when BAO and HST data are included in the standard neutrino models.

SPT data exclude standard dark radiation viscosity at 2 sigma when considering dark radiation with unknown clustering.

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 (WMAP9), 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 Neff 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 Neff massive neutrino case the two high multipole probes give very different results regardless of the external data sets used in the combined analyses. 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 cvis=1/3 at the 2 sigma CL, finding evidence for massive neutrinos only when combining SPT data with BAO measurements.