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A new life for sterile neutrinos: resolving inconsistencies using hot dark matter

Jan Hamann, Jasper Hasenkamp

TL;DR

The paper tackles tensions between Planck CMB results and local probes of $H_0$ and small-scale structure by testing a ΛCDM extension with hot dark matter, modeled as a sterile-neutrino-like component characterized by $ΔN_ ext{eff}$ and $m_s^ ext{eff}$. By combining Planck with WMAP-9 polarization, BAO, the HST $H_0$ measurement, Planck cluster counts, and CFHTLenS lensing within a CosmoMC analysis, they find $ΔN_ ext{eff} = 0.61 \,±\,0.30$ and $m_s^ ext{eff} = 0.41 \,±\,0.13$ eV (1σ). CFHTLenS tensions favor non-zero $ΔN_ ext{eff}$ and mass; the full data set yields a significantly better fit than vanilla ΛCDM ($Δχ^2 = -13.2$) and suggests HDM at ~$3σ$, while some sterile-neutrino scenarios from reactor/gallium data are strongly disfavored or in tension. These results motivate a non-negligible hot dark matter fraction in the early Universe and point to future Planck polarization and large-volume surveys to decisively test the hypothesis.

Abstract

Within the standard LCDM model of cosmology, the recent Planck measurements have shown discrepancies with other observations, e.g., measurements of the current expansion rate H_0, the galaxy shear power spectrum and counts of galaxy clusters. We show that if LCDM is extended by a hot dark matter component, which could be interpreted as a sterile neutrino, the data sets can be combined consistently. A combination of Planck data, WMAP-9 polarisation data, measurements of the BAO scale, the HST measurement of H_0, Planck galaxy cluster counts and galaxy shear data from the CFHTLens survey yields Delta N_eff = 0.61 pm 0.30 and m_s^eff = (0.41 pm 0.13) eV at 1 sigma. The former is driven mainly by the large H_0 of the HST measurement, while the latter is driven by cluster data. CFHTLens galaxy shear data prefer Delta N_eff >0 and a non-zero mass. Taken together, we find hints for the presence of a hot dark matter component at 3 sigma. A sterile neutrino motivated by the reactor and gallium anomalies appears rejected at even higher significance and an accelerator anomaly sterile neutrino is found in tension at 2 sigma.

A new life for sterile neutrinos: resolving inconsistencies using hot dark matter

TL;DR

The paper tackles tensions between Planck CMB results and local probes of and small-scale structure by testing a ΛCDM extension with hot dark matter, modeled as a sterile-neutrino-like component characterized by and . By combining Planck with WMAP-9 polarization, BAO, the HST measurement, Planck cluster counts, and CFHTLenS lensing within a CosmoMC analysis, they find and eV (1σ). CFHTLenS tensions favor non-zero and mass; the full data set yields a significantly better fit than vanilla ΛCDM () and suggests HDM at ~, while some sterile-neutrino scenarios from reactor/gallium data are strongly disfavored or in tension. These results motivate a non-negligible hot dark matter fraction in the early Universe and point to future Planck polarization and large-volume surveys to decisively test the hypothesis.

Abstract

Within the standard LCDM model of cosmology, the recent Planck measurements have shown discrepancies with other observations, e.g., measurements of the current expansion rate H_0, the galaxy shear power spectrum and counts of galaxy clusters. We show that if LCDM is extended by a hot dark matter component, which could be interpreted as a sterile neutrino, the data sets can be combined consistently. A combination of Planck data, WMAP-9 polarisation data, measurements of the BAO scale, the HST measurement of H_0, Planck galaxy cluster counts and galaxy shear data from the CFHTLens survey yields Delta N_eff = 0.61 pm 0.30 and m_s^eff = (0.41 pm 0.13) eV at 1 sigma. The former is driven mainly by the large H_0 of the HST measurement, while the latter is driven by cluster data. CFHTLens galaxy shear data prefer Delta N_eff >0 and a non-zero mass. Taken together, we find hints for the presence of a hot dark matter component at 3 sigma. A sterile neutrino motivated by the reactor and gallium anomalies appears rejected at even higher significance and an accelerator anomaly sterile neutrino is found in tension at 2 sigma.

Paper Structure

This paper contains 6 sections, 2 equations, 3 figures, 3 tables.

Table of Contents

  1. Introduction
  2. Models and Data
  3. Models
  4. Data
  5. Results
  6. Conclusions

Figures (3)

  • Figure 1: Posterior probabilities (normalised to their respective maximum values) for the extra parameters of the sterile model.
  • Figure 2: Joint 68%- and 95%-credible contours of the marginalised posterior for the extra parameters of the sterile model. Red contours correspond to CMB data only, while the blue contours represent the full data combination. The vanilla model is located at the origin. Fully thermalised neutrinos correspond to $\Delta N_\text{eff}=1$ by construction. Parameter values corresponding to a low mass sterile neutrino as motivated by the reactor and gallium anomalies are marked with an asterisk (*). A small region around the point marked by a cross (+) is motivated by the accelerator anomaly.
  • Figure 3: Joint 68%- and 95%-credible contours of the marginalised posterior, illustrating the correlations between the extra parameters of the sterile model and the parameters $\sigma_8$, $H_0$ and $\Omega_\mathrm{m}$. Red contours correspond to CMB data only, blue contours represent the full data combination.