Wednesday, July 31, 2013

1307.7715 (Mark Wyman et al.)

nu-LCDM: Neutrinos reconcile Planck with the Local Universe    [PDF]

Mark Wyman, Douglas H. Rudd, R. Ali Vanderveld, Wayne Hu
Current measurements of the low and high redshift Universe are in tension if we restrict ourselves to the standard six parameter model of flat LCDM. This tension has two parts. First, the Planck satellite suggests a higher normalization of matter perturbations than local measurements of galaxy clusters. Second, the expansion rate of the Universe today, H_0, derived from local distance-redshift measurements is significantly higher than that inferred using the acoustic scale in galaxy surveys and the Planck data as a standard ruler. The addition of a sterile neutrino species changes the acoustic scale and brings the two into agreement; meanwhile, adding mass to the active neutrinos or to a sterile neutrino can suppress the growth of structure, bringing the cluster data into concordance as well. For our fiducial dataset combination, with statistical errors for clusters, a model with a massive sterile neutrino shows 3.5 sigma evidence for a non-zero mass and an even stronger rejection of the minimal model. A model with massive active neutrinos and a massless sterile neutrino is similarly preferred. An eV-scale sterile neutrino mass -- suggested by short baseline and reactor anomalies -- is well within the allowed range.
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