Constraints on the neutrino mass and mass hierarchy from cosmological observations

TL;DR

This paper tackles the cosmological constraints on neutrino properties by incorporating the mass splitting among the three active neutrinos into an updated analysis of anisotropic BAO measurements from BOSS DR12 CMASS and LOWZ, complemented by Planck 2015 CMB data. Using a $\nu\Lambda$CDM framework and CosmoMC, the authors assess NH, IH, and DH mass hierarchies and derive tight upper bounds on $\sum m_\nu$, while also constraining the effective number of relativistic species $N_{\textrm{eff}}$ and the presence of sterile neutrinos via $m_{\nu,\textrm{sterile}}^{\textrm{eff}}$. Their results show 95% C.L. bounds of $\sum m_\nu<0.18$ eV (NH), $<0.20$ eV (IH), and $<0.15$ eV (DH) for Planck TT,TE,EE+lowP+BAO, and looser bounds for Planck TT+lowP+lensing+BAO, with a slight preference for NH ($\Delta\chi^2\approx-3.4$). They find no evidence for extra $N_{\textrm{eff}}$ or fully thermalized sterile neutrinos, reinforcing the standard cosmological model's neutrino sector, and demonstrate that DR12 provides meaningful, albeit still inconclusive, sensitivity to neutrino mass hierarchy. The work highlights the potential for future data to decisively determine the hierarchy and the role of sterile species in cosmology.

Abstract

Considering the mass splitting between three active neutrinos, we represent the new constraints on the sum of neutrino mass $\sum m_ν$ by updating the anisotropic analysis of Baryon Acoustic Oscillation (BAO) scale in the CMASS and LOWZ galaxy samples from Data Release 12 of the SDSS-III Baryon Oscillation Spectroscopic Survey (BOSS DR12). Combining the BAO data of 6dFGS, MGS, LOWZ and CMASS with $\textit{Planck}$~2015 data of temperature anisotropy and polarizations of Cosmic Microwave Background (CMB), we find that the $95\%$ C.L. upper bounds on $\sum m_ν$ refer to $\sum m_{ν,\rm NH}<0.18$ eV for normal hierarchy (NH), $\sum m_{ν,\rm IH}<0.20$ eV for inverted hierarchy (IH) and $\sum m_{ν,\rm DH}<0.15$ eV for degenerate hierarchy (DH) respectively, and the normal hierarchy is slightly preferred than the inverted one ($Δχ^2\equiv χ^2_{\rm NH}-χ^2_{\rm IH} \simeq -3.4$). In addition, the additional relativistic degrees of freedom and massive sterile neutrinos are neither favored at present.

Figures (1)

• Figure 1: The likelihood distributions of $m_{\nu,\textrm{min}}$ and $\sum m_\nu$ for the NH, IH and DH of neutrinos in the $\nu\Lambda$CDM models from two data combinations of $\textit{Planck}$ TT,TE,EE+lowP+BAO and $\textit{Planck}$ TT+lowP+lensing+BAO, respectively.