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

TL;DR

Extending the standard cosmological model with a hot dark matter component, possibly a sterile neutrino, reconciles various observational discrepancies and suggests a 3 sigma hint for such a component.

Contribution

This paper demonstrates that adding a hot dark matter component, interpreted as a sterile neutrino, resolves inconsistencies among cosmological data sets.

Findings

Hints for hot dark matter at 3 sigma significance

Delta N_eff = 0.61 ± 0.30, m_s^eff = 0.41 ± 0.13 eV

Sterile neutrino models from reactor and gallium anomalies are disfavored

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.