Cosmological search for sterile neutrinos after DESI 2024

TL;DR

This study tests cosmological constraints on massive sterile neutrinos across three dark-energy models (ΛCDM+Sterile, wCDM+Sterile, w0w_a+Sterile) using DESI BAO, DESY5 SN, DESY1/DESY3 weak-lensing data, and Planck/ACT CMB measurements. The analysis employs Bayesian model comparison and a high-dimensional evidence estimator to assess the existence of sterile neutrinos, finding no evidence in ΛCDM+Sterile or wCDM+Sterile, but a ~2σ hint of nonzero sterile mass in the time-varying dark-energy model with CBS+DESY3, namely $m_{ u,\rm sterile}^{\rm eff}=0.50^{+0.33}_{-0.27}$ eV and $N_{ m eff}=3.076^{+0.011}_{-0.017}$ with $\Delta N_{ m eff}>0$. The results also show that DESY3 weak-lensing data lowers $S_8$, which interacts with sterile-neutrino mass constraints, and that including the total active-neutrino mass $\sum m_\nu$ weakens or eliminates the sterile signal, reducing Bayesian evidence for sterile scenarios relative to ΛCDM. Overall, the work highlights the sensitivity of sterile-neutrino constraints to the assumed dark-energy model and the importance of combining CMB with large-scale structure data, while pointing to future surveys as crucial for robust detection or exclusion.

Abstract

The question of whether the massive sterile neutrinos exist remains a crucial unresolved issue in both particle physics and cosmology. We explore the cosmological constraints on the massive sterile neutrinos using the latest observational data, including the baryon acoustic oscillations data from DESI, the cosmic microwave background data from Planck satellite and ACT, and the 5-year Type Ia supernova data and the 3-year weak-lensing data from DES. We search for the massive sterile neutrinos within the $Λ$CDM, $w$CDM, and $w_0w_a$CDM models. Our analysis shows that when considering massive sterile neutrinos within the $w_0w_a\rm CDM$ model, the combined datasets allow us to infer a non-zero sterile neutrino mass at approximately $2σ$ confidence level. Specifically, in the $w_0w_a$CDM+Sterile model, the effective mass of sterile neutrinos and the effective number of relativistic species are constrained to be $m_{ν,\ \mathrm{sterile}}^{\mathrm{eff}} = 0.50^{+0.33}_{-0.27} \, \mathrm{eV}$ and $N_\mathrm{eff} = 3.076^{+0.011}_{-0.017}$, respectively. However, the $Λ$CDM+Sterile and $w$CDM+Sterile models could not provide evidence supporting the existence of massive sterile neutrinos.

Figures (5)

• Figure 1: The 1$\sigma$ and 2$\sigma$ credible-interval contours of $m_{\nu,\ \rm sterile}^{\rm eff}$, $H_0$, $S_8$, and $N_{\rm eff}$ in the $\Lambda$CDM+Sterile model, using the CBS, CBS+DESY1, and CBS+DESY3 data combinations, respectively.
• Figure 2: The 1$\sigma$ and 2$\sigma$ credible-interval contours of $m_{\nu,\ \rm sterile}^{\rm eff}$, $H_0$, $w$, and $N_{\rm eff}$ in the $w$CDM+Sterile model, using the CBS, CBS+DESY1, and CBS+DESY3 data combinations, respectively.
• Figure 3: The triangular plots of the marginalized posterior distributions for cosmological parameters in the $w_0w_a$CDM+Sterile model, using the CBS, CBS+DESY1, and CBS+DESY3 data combinations, respectively.
• Figure 4: The Bayes factors of the $\Lambda$CDM+Sterile, $w$CDM+Sterile, $w_0w_a$CDM+Sterile, and $w_0w_a$CDM+Sterile+$\sum m_\nu$ models, relative to the $\Lambda$CDM model, calculated using the CBS+DESY3 data (marked in magenta, orange, blue, and green respectively). The shades of gray from light to dark represent inconclusive, weak, moderate, and strong evidence based on Jeffreys' scale. The negative values of $\ln \mathcal{B}_{ij}$ indicate that the $\Lambda$CDM model is preferred.
• Figure 5: The 1$\sigma$ and 2$\sigma$ credible-interval contours of $m_{\nu,\ \rm sterile}^{\rm eff}$, $H_0$, $S_8$, $\sum m_\nu$, and $N_{\rm eff}$ in the $w_0w_a$CDM+Sterile+$\sum m_\nu$ model, using the CBS, CBS+DESY1, and CBS+DESY3 datasets, respectively.