Testing 3+1 and 3+2 neutrino mass models with cosmology and short baseline experiments

TL;DR

The study tests the viability of 3+1 and 3+2 sterile-neutrino models by combining short-baseline oscillation data with cosmological observations. It performs SBL fits (χ^2 and Bayesian) to map $Δm^2_{41}$, $Δm^2_{51}$ and mixing, and analyzes cosmology with fixed $N_eff$ using CosmoMC on CMB and large-scale structure data to bound $m_4$ and $m_5$. A joint Bayesian combination of the marginal posteriors shows that a single sterile around ~1 eV is marginally compatible with both datasets when galaxy clustering is not included, while including such data induces tension and tightens the allowed region. The results imply that, while one massive sterile neutrino near 1 eV remains plausible, introducing a second sterile at higher mass is disfavored by cosmology, highlighting persistent tension between SBL hints and cosmological bounds for multi-sterile scenarios.

Abstract

Recent results from short--baseline neutrino oscillation experiments and Cosmic Microwave Background anisotropy measurements suggest the presence of additional sterile neutrinos. In this paper we properly combine these data sets to derive bounds on the sterile neutrino masses in the 3+1 and 3+2 frameworks, finding a potentially good agreement between the two datasets. However, when galaxy clustering is included in the analysis a tension between the oscillation and cosmological data is clearly present.

Figures (6)

• Figure 1: Allowed regions in the $\sin^{2}2\vartheta_{e\mu}$--$\Delta{m}^2_{41}$, $\sin^{2}2\vartheta_{ee}$--$\Delta{m}^2_{41}$ and $\sin^{2}2\vartheta_{\mu\mu}$--$\Delta{m}^2_{41}$ planes obtained from the global fit of short--baseline neutrino oscillation data in the 3+1 scheme using the standard $\chi^2$ method. The best-fit point is indicated by a cross (see Table. \ref{['tab:sbl']}).
• Figure 2: Allowed regions in the $\Delta m_{41}^2$-$\Delta m_{51}^2$ plane and corresponding marginal $\Delta\chi^2$'s obtained from the global fit of short--baseline neutrino oscillation data in 3+2 schemes using the standard $\chi^2$ method. The best-fit point is indicated by a cross (see Table. \ref{['tab:sbl']}).
• Figure 3: Marginal posterior probabilities obtained with a Bayesian analysis for $\Delta m_{41}^2$ in the 3+1 scheme. The thick [green] solid line exhibiting several sharp peaks (the same in the two panels) refers to the analysis of the short--baseline oscillation data alone. The blue line exhibiting a broad peak stands for the analysis of the cosmological data alone: CMB-only data for the left panel, CMB data implemented with SDSS and HST information for the right panel. In all cases, the shaded regions refer to the 95% coverage of the probability distribution.
• Figure 4: Allowed regions in the $\Delta m_{41}^2$-$\Delta m_{51}^2$ plane obtained with a Bayesian analysis. The "boxy" regions (the same in the two panels) refer to the global analysis of the short--baseline oscillation data and are relative to the following confidence levels (from the innermost to the outermost region): 68.27% (red), 90.00% (light blue), 95.45% (green), 99.00% (brown) and 99.73% (dark blue). The arc--shaped solid lines refer to the analysis of the cosmological data: the left panel stands for the CMB--only dataset, while the right panel refers to the inclusion of the SDSS information and HST prior to the CMB data. The different lines refer to the following confidence levels (from the lower curve to the upper curve, in each panel): 68.27% , 90.00%, 95.45%, 99.00% and 99.73% .
• Figure 5: Marginal posterior probabilities obtained with a Bayesian analysis for $\Delta m_{41}^2$ in the 3+1 scheme, for the joint analysis of cosmological and short--baseline data. Left panel: the cosmological analysis employs CMB--only data. Right panel: the cosmological analysis adds SDSS and HST information to the CMB data. The horizontal dashed lines identify (from the lower curve to the upper curve, in each panel) the credible intervals at 68.27%, 90.00%, 95.45%, 99.00% and 99.73% C.L.