Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

Statistical tests of sterile neutrinos using cosmology and short-baseline data

Johannes Bergström, M. C. Gonzalez-Garcia, V. Niro, J. Salvado

TL;DR

The paper addresses whether cosmological observations support sterile neutrinos proposed to explain short-baseline anomalies by performing Bayesian model comparison between 3+1 and 3+0 scenarios across multiple data sets. It computes marginalized cosmological likelihoods in ($m_{ m eff}, N_{ m eff}$) within a ΛCDM+$r$+$ν_s$ framework, and then tests the compatibility of these cosmological results with SBL data using Bayes factors and consistency checks. Without Planck SZ/HST data, cosmology tends to disfavor the 3+1 model unless the sterile contribution to radiation density is suppressed; with cluster data included, there can be a window where 3+1 is moderately favored for intermediate $\Delta N_{ m eff}$, but significant tensions between cosmology and SBL masses remain. Overall, the work indicates that fully thermalized eV-scale sterile neutrinos are difficult to reconcile with current cosmological data, unless new physics reduces their early-Universe radiation density, impacting interpretations of SBL anomalies.

Abstract

In this paper we revisit the question of the information which cosmology provides on the scenarios with sterile neutrinos invoked to describe the SBL anomalies using Bayesian statistical tests. We perform an analysis of the cosmological data in $Λ$CDM$+r+ν_s$ cosmologies for different cosmological data combinations, and obtain the marginalized cosmological likelihood in terms of the two relevant parameters, the sterile neutrino mass $m_s$ and its contribution to the energy density of the early Universe $N_{\rm eff}$. We then present an analysis to quantify at which level a model with one sterile neutrino is (dis)favoured with respect to a model with only three active neutrinos, using results from both short-baseline experiments and cosmology. We study the dependence of the results on the cosmological data considered, in particular on the inclusion of the recent BICEP2 results and the SZ cluster data from the Planck mission. We find that only when the cluster data is included the model with one extra sterile neutrino can become more favoured that the model with only the three active ones provided the sterile neutrino contribution to radiation density is suppressed with respect to the fully thermalized scenario. We have also quantified the level of (in)compatibility between the sterile neutrino masses implied by the cosmological and SBL results.

Statistical tests of sterile neutrinos using cosmology and short-baseline data

TL;DR

The paper addresses whether cosmological observations support sterile neutrinos proposed to explain short-baseline anomalies by performing Bayesian model comparison between 3+1 and 3+0 scenarios across multiple data sets. It computes marginalized cosmological likelihoods in () within a ΛCDM++ framework, and then tests the compatibility of these cosmological results with SBL data using Bayes factors and consistency checks. Without Planck SZ/HST data, cosmology tends to disfavor the 3+1 model unless the sterile contribution to radiation density is suppressed; with cluster data included, there can be a window where 3+1 is moderately favored for intermediate , but significant tensions between cosmology and SBL masses remain. Overall, the work indicates that fully thermalized eV-scale sterile neutrinos are difficult to reconcile with current cosmological data, unless new physics reduces their early-Universe radiation density, impacting interpretations of SBL anomalies.

Abstract

In this paper we revisit the question of the information which cosmology provides on the scenarios with sterile neutrinos invoked to describe the SBL anomalies using Bayesian statistical tests. We perform an analysis of the cosmological data in CDM cosmologies for different cosmological data combinations, and obtain the marginalized cosmological likelihood in terms of the two relevant parameters, the sterile neutrino mass and its contribution to the energy density of the early Universe . We then present an analysis to quantify at which level a model with one sterile neutrino is (dis)favoured with respect to a model with only three active neutrinos, using results from both short-baseline experiments and cosmology. We study the dependence of the results on the cosmological data considered, in particular on the inclusion of the recent BICEP2 results and the SZ cluster data from the Planck mission. We find that only when the cluster data is included the model with one extra sterile neutrino can become more favoured that the model with only the three active ones provided the sterile neutrino contribution to radiation density is suppressed with respect to the fully thermalized scenario. We have also quantified the level of (in)compatibility between the sterile neutrino masses implied by the cosmological and SBL results.

Paper Structure

This paper contains 12 sections, 20 equations, 4 figures, 3 tables.

Table of Contents

  1. Introduction
  2. The statistical framework
  3. Model comparison
  4. Parameters of interest and the marginal likelihood
  5. Cosmological analysis
  6. Data sets
  7. Cosmological model
  8. Marginal cosmological likelihoods
  9. Test on sterile neutrinos models
  10. Sterile neutrinos vs none
  11. Consistency of parameter constraints
  12. Summary

Figures (4)

  • Figure 1: Marginal likelihood of $(m_{\rm eff},\Delta N_{\rm eff})$ (upper right panel) and of $(m_{s},\Delta N_{\rm eff})$ for thermally distributed $\nu_s$ (upper left panel) and for the for DW scenario (lower panel) for the CMB+BAO cosmological data set ( SET 1). Black dashed contours are those of $-2 \log(\mathcal{L}/\mathcal{L}^{\rm max})<C$, which would correspond to nominal 1,2,3 sigma levels. The red line denotes the region for which $m_s =10$ eV for thermal $\nu_s$.
  • Figure 2: Same two upper panels in Fig. \ref{['fig:set1']}, but for CMB+BAO+BICEP2 cosmological data ( SET 2, upper panels), and CMB+BAO+BICEP2+HST+PlaSZ cosmological data ( SET 3, lower panels).
  • Figure 3: Marginal likelihoods as function of $m_{s}$ for fixed $\Delta N_{\rm eff}$ ($\Delta N_{\rm eff}= 0.1, 0.3, 0.6, 1$) and for thermal $\nu_s$ (solid lines) and for the DW scenario (dashed lines). We show the results for the three cosmological data sets used as labeled in the figure. In all panels we also include the marginal likelihood for the SBL analysis in the 3+1 scenario (marginalized with respect to the lighter neutrino masses and all mixings) as given in Fig.1 in Ref. Kristiansen:2013mza. We denote by the red arrow the width and height of the box used to define "box SBL likelihood" (see text for details).
  • Figure 4: Left panels:Logarithm of the Bayes factor $\mathcal{B}_{10}^\text{upd}$ as a function of $\Delta N_{\rm eff}$. Right panels: Consistency of mass constraints. In all panels the results are shown for thermal $\nu_s$ (solid lines) and for the DW scenario (dashed lines) and for the SBL full (black) and Box likelihood (red). We show the results for the three cosmological data sets considered: CMB+BAO (upper row), CMB+BAO+BICEP2 (middle row), CMB+BAO+BICEP2+HST+PlaSZ (lower row).