No new cosmological concordance with massive sterile neutrinos

TL;DR

The paper investigates whether incorporating massive sterile neutrinos can establish a new cosmological concordance among CMB, LSS, and local $H_0$ measurements. Using CosmoMC to fit an extended $ ext{ΛCDM}$ framework (with active and sterile neutrinos) to a wide array of data (Planck CMB, WMAP polarization, ACT/SPT, Planck lensing, BAO, CFHTLenS, PlaSZ, X-ray clusters, RSD, $H_0$, and clustering data), it evaluates Bayesian evidence against the minimal model. The results show that extended neutrino models are not preferred by the data; robust combinations yield tight limits $\sum m_ u \lesssim 0.3$ eV and $m_{ u,\text{sterile}}^{\text{eff}} \lesssim 0.3$ eV at $95\%$ CL, and the tension between Planck CMB and cluster measurements persists even with the extended parameter space, including tensor modes. The study concludes that there is no evidence for large neutrino masses or additional neutrino species within current cosmological data, and if the tension remains, new physics beyond massive neutrinos or unresolved systematics must be considered. Bayesian evidence consistently disfavors the extended models relative to ΛCDM across data combinations.

Abstract

It has been claimed recently that massive sterile neutrinos could bring about a new concordance between observations of the cosmic microwave background (CMB), the large-scale structure (LSS) of the Universe, and local measurements of the Hubble constant, $H_0$. We demonstrate that this apparent concordance results from combining datasets which are in significant tension, even within this extended model, possibly indicating remaining systematic biases in the measurements. We further show that this tension remains when the cosmological model is further extended to include significant tensor modes, as suggested by the recent BICEP2 results. Using the Bayesian evidence, we show that the minimal $Λ$CDM model is strongly favoured over its neutrino extensions by various combinations of datasets. Robust data combinations yield stringent limits of $\sum m_ν\lesssim0.3$ eV and $m_{ν,{\rm sterile}}^{\rm eff} \lesssim 0.3$ eV at $95\%$ CL for the sum of active and sterile neutrinos, respectively.

Figures (3)

• Figure 1: Constraints on the $\Lambda$CDM+${\rm N}_{\rm eff}+m_{\nu,{\rm sterile}}^{\rm eff}$ model, showing that non-zero sterile neutrino mass is only favoured as a result of a tension between the CMB and cluster data (PlaSZ, X-ray) in the $\sigma_8$--$\Omega_m$ plane, and the degeneracy between $\sigma_8$ and neutrino mass.
• Figure 2: Persistence of the tension as the minimal $\Lambda$CDM model is extended in the neutrino sector, i.e., as ${\rm N}_{\rm eff}$ and massive active or sterile neutrinos are added.
• Figure 3: Constraints on the $\Lambda$CDM$+\ r_{0.002}+{\rm N}_{\rm eff}+m_{\nu,{\rm sterile}}^{\rm eff}$ model, illustrating the persisting tension between X-ray clusters and CMB+BAO in the $\sigma_8$--$\Omega_m$ plane, despite an apparent reconciliation of the BICEP and Planck results on $r_{0.002}$.