Neutrino and Dark Radiation properties in light of latest CMB observations
Maria Archidiacono, Elena Giusarma, Alessandro Melchiorri, Olga Mena
TL;DR
The paper assesses neutrino masses and dark radiation properties using recent high-$ l$ CMB data from SPT and ACT, complemented by WMAP9, BAO, HST, and SNLS3. By exploring standard $ m \Lambda CDM$ with three massive neutrinos, $N_{ extrm{eff}}$ scenarios, and dark radiation with clustering parameters $c^2_{ extrm{eff}}$ and $c^2_{ extrm{vis}}$, it finds that SPT and ACT yield divergent implications for $amily{ ext{sum}} u$ and $N_{ extrm{eff}}$, with BAO and HST data mitigating but not eliminating the tension. In extended models, the degeneracy with $w$ or $n_{ extrm{run}}$ weakens neutrino mass bounds and pushes $N_{ extrm{eff}}$ higher in some cases, while SPT disfavors $c^2_{ extrm{vis}}=1/3$ for a dark radiation component; ACT results remain more consistent with standard clustering. The results underscore persistent inconsistencies that Planck-era data are expected to resolve, informing future Majorana neutrino searches and our understanding of relativistic degrees of freedom in the early universe.
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.