On the improvement of cosmological neutrino mass bounds

TL;DR

The paper addresses how cosmology constrains the sum of neutrino masses by leveraging Planck CMB data, the full-shape DR9 galaxy power spectrum, BAO, and H0 priors within a ΛCDM+∑mν framework. It uses HaloFit with massive-neutrino corrections and explores different mass spectra (one massive, two massive, degenerate) under various low-redshift priors, employing MCMC to derive robust upper limits. The results show tight 95% CL bounds (e.g., ∑mν<0.183 eV with Planck TT+DR9, tightening to 0.176 eV with Planck pol) and demonstrate that including BAO and strong H0 priors can push limits down to ~0.125 eV for the one-massive case, while disfavouring degenerate spectra and mildly disfavouring inverted hierarchy. These findings underscore the sensitivity of cosmological neutrino mass bounds to low-redshift parameters and mass-scheme choices, and they motivate future joint cosmological-laboratory analyses to better determine the neutrino mass ordering.

Abstract

The most recent measurements of the temperature and low-multipole polarization anisotropies of the Cosmic Microwave Background (CMB) from the Planck satellite, when combined with galaxy clustering data from the Baryon Oscillation Spectroscopic Survey (BOSS) in the form of the full shape of the power spectrum, and with Baryon Acoustic Oscillation measurements, provide a $95\%$ confidence level (CL) upper bound on the sum of the three active neutrinos $\sum m _ν< 0.183$ eV, among the tightest neutrino mass bounds in the literature, to date, when the same datasets are taken into account. This very same data combination is able to set, at $\sim70\%$ CL, an upper limit on $\sum m _ν$ of $0.0968$ eV, a value that approximately corresponds to the minimal mass expected in the inverted neutrino mass hierarchy scenario. If high-multipole polarization data from Planck is also considered, the $95\%$ CL upper bound is tightened to $\sum m _ν< 0.176$ eV. Further improvements are obtained by considering recent measurements of the Hubble parameter. These limits are obtained assuming a specific non-degenerate neutrino mass spectrum; they slightly worsen when considering other degenerate neutrino mass schemes. Current cosmological data, therefore, start to be mildly sensitive to the neutrino mass ordering. Low-redshift quantities, such as the Hubble constant or the reionization optical depth, play a very important role when setting the neutrino mass constraints. We also comment on the eventual shifts in the cosmological bounds on $\sum m_ν$ when possible variations in the former two quantities are addressed.

Figures (3)

• Figure 1: Top: Non-linear matter power spectrum computed using the HaloFit method with the CAMB code Lewis:1999bs (blue line) and the Coyote emulator (green line) of Kwan et al. (2015) Kwan:2013jva at z=0.57 for the $\Lambda$CDM best-fit parameters from Planck TT 2015 data. Data points are the clustering measurements from the BOSS Data Release 9 (DR9) CMASS sample. The error bars are computed from the diagonal elements $C_{ii}$ of the covariance matrix. We also illustrate the data after applying a maximal correction for systematics, i.e. $S=1$; see text for details. Bottom: Residuals with respect to the non linear model with HaloFit. The orange horizontal line indicates the $k$ range used in our analysis.
• Figure 2: One-dimensional posterior probability for $\sum m_\nu$ for the Base combination, which consists of Planck TT and DR9 galaxy clustering measurements, and also combined with other possible data sets. Both the one (solid) and the two (dashed) massive neutrino cases are illustrated.
• Figure 3: As in Fig. \ref{['fig:probfigmnu']} but focusing on the Base combination only. Different curves show the impact of marginalizing over bias, shot noise and systematics; see text for details.