Possible indication for non-zero neutrino mass and additional neutrino species from cosmological observations

TL;DR

Cosmological observations suggest the possibility of non-zero neutrino mass and additional neutrino species, which can resolve discrepancies in standard cosmological model parameters and improve data fit.

Contribution

This paper provides evidence that including extra neutrino species and neutrino mass in the LCDM model significantly improves fit to cosmological data.

Findings

Extra neutrino species (N_eff ≈ 4) improve data fit.

Non-zero neutrino mass (~0.5 eV) is favored by galaxy cluster data.

Discrepancies in Hubble constant and fluctuation amplitude are alleviated.

Abstract

The constraints on total neutrino mass and effective number of neutrino species based on CMB anisotropy power spectrum, Hubble constant, baryon acoustic oscillations and galaxy cluster mass function data are presented. It is shown that the discrepancies between various cosmological data in Hubble constant and density fluctuation amplitude, measured in standard LCDM cosmological model, can be eliminated if more than standard effective number of neutrino species and non-zero total neutrino mass are considered. This extension of LCDM model appears to be \approx 3 \sigma\ significant when all cosmological data are used. The model with approximately one additional neutrino type, N_eff \approx 4, and with non-zero total neutrino mass, \approx 0.5 eV, provide the best fit to the data. In the model with only one massive neutrino the upper limits on neutrino mass are slightly relaxed. It is shown that these deviations from LCDM model appear mainly due to the usage of recent data on the observations of baryon acoustic oscillations. Larger than standard number of neutrino species is measured mainly due to the comparison of the BAO data with direct measurements of Hubble constant, which was already noticed earlier. As it is shown below, the data on galaxy cluster mass function in this case give the measurement of non-zero neutrino mass.