Neutrino constraints: what large-scale structure and CMB data are telling us?

TL;DR

This paper interrogates the reliability of cosmological neutrino-mass constraints by performing a full likelihood analysis across CMB data (WMAP9 or Planck) and multiple low-redshift probes (BAO, CFHTLenS, Ly-$\alpha$, and cluster counts), while carefully treating halo mass-function calibrations and mass-bias systematics. It finds that low-redshift probes alone do not reveal neutrino masses, but combinations with CMB+BAO yield detections at the $>2\sigma$ level, with stronger indications in sterile-neutrino scenarios. In active neutrino models, joint analyses with Planck+BAO+Ly-$\alpha$ tighten upper bounds to $\sim 0.14$ eV, whereas in sterile-neutrino models, Planck+BAO+Cluster suggests $m_\text{s}^{\rm eff}$ around several tenths of an eV and $\Delta N_{\rm eff}$ of order unity, though Ly-$\alpha$ data pull masses down. The full data combination indicates a mild preference for nonzero sterile neutrino mass, $m_\text{s}^{\rm eff} \approx 0.26^{+0.22}_{-0.24}$ eV with $\Delta N_{\rm eff} \approx 0.82\pm0.55$, while active-neutrino masses remain upper-limited; the results are sensitive to systematics in cluster mass calibration and intrinsic alignments, underscoring the need for improved modeling and future surveys to robustly constrain neutrino properties.

Abstract

(Abridged) We discuss the reliability of neutrino mass constraints, either active or sterile, from the combination of WMAP 9-year or Planck CMB data with BAO measurements from BOSS DR11, galaxy shear measurements from CFHTLenS, SDSS Ly-$α$ forest constraints and galaxy cluster mass function from Chandra observations. To avoid model dependence of the constraints we perform a full likelihood analysis for all the datasets employed. As for the cluster data analysis we rely on to the most recent calibration of massive neutrino effects in the halo mass function and we explore the impact of the uncertainty in the mass bias and re-calibration of the halo mass function due to baryonic feedback processes on cosmological parameters. We find that none of the low redshift probes alone provide evidence for massive neutrinos in combination with CMB measurements, while a larger than $2σ$ detection of non zero neutrino mass, either active or sterile, is achieved combining cluster or shear data with CMB and BAO measurements. The preference for massive neutrino is larger in the sterile neutrino scenario, and for the combination of Planck, BAO, shear and cluster datasets we find that the vanilla $Λ$CDM model is rejected at more than $3σ$ and a sterile neutrino mass as motivated by accelerator anomaly is within the $2σ$ errors. Finally, results from the full data combination reflect the tension between the $σ_8$ constraints obtained from cluster and shear data and that inferred from Ly-$α$ forest measurements; in the active neutrino scenario for both CMB datasets employed, the full data combination yields only an upper limits on $\sum m_ν$, while assuming an extra sterile neutrino we still get preference for non-vanishing mass, $m_s^{\rm eff}=0.26^{+0.22}_{-0.24}$ eV, and dark contribution to the radiation content, $ΔN_{\rm eff}=0.82\pm0.55$.

Figures (7)

• Figure 1: Summary of the $1\sigma$ and $2\sigma$ errors on $\sum m_\nu$ obtained from the dataset combinations discussed in section \ref{['sub:mnu']} within a $\Lambda$CDM+$\sum m_\nu$ model.
• Figure 2: Left -Joint 68% and 95% CL contours in the $\sigma_8 - (\Omega_{\rm m},H_0,\sum m_\nu)$ planes for a $\Lambda$CDM+$\sum m_\nu$ model from the combination of WMAP9 (upper panels) or Planck (lower panels) data with different low redshift Universe probes. Right - Posterior probability distribution for $\sum m_\nu$ from the same data combination.
• Figure 3: Left -Confidence contours at 68% and 95% CL in the $\sigma_8 - (\Omega_{\rm m},H_0,\sum m_\nu)$ planes when combining WMAP9 (upper panels) or Planck (lower panels) with many different probes of the low redshift Universe within a $\Lambda$CDM+$\sum m_\nu$ model. Right - Posterior probability distribution for $\sum m_\nu$ from the same datasets.
• Figure 4: Left-Middle panel - Comparison of the confidence contours at 68% and 95% CL in the $\sigma_8 - \Omega_{\rm m}$ plane within a $\Lambda$CDM+$\sum m_\nu$ model when combining WMAP9 (left panel) or Planck (middle panel) with cluster data using different prescriptions: the standard one (Cluster), the baryon correction (Cluster(BC)) or marginalizing over the bias (Cluster($B_M$)). In the middle panel are also shown the confidence contours for the joint analysis Planck+BAO: only when $B_M$ is allowed to vary the Planck+BAO and Planck+Cluster($B_M$) regions overlap. Right panel - Joint 68% and 95% CL constraints on $\sigma_8 - \Omega_{\rm m}$ for different dataset combined with Planck with the $A_{\rm L}$-lensing signal marginalized out.
• Figure 5: Summary of the $1\sigma$ and $2\sigma$ errors on $m_{\rm s}^{\rm eff}$ and $N_\text{eff}$ obtained from the dataset combinations discussed in section \ref{['sub:meff']} for a $\Lambda$CDM+$m_{\rm s}^{\rm eff}$+$N_\text{eff}$ model with one massive neutrino of mass $m_\nu=0.06$ eV.