Neutrinos Help Reconcile Planck Measurements with the Local Universe

Abstract

Current measurements of the low and high redshift Universe are in tension if we restrict ourselves to the standard six-parameter model of flat ΛCDM. This tension has two parts. First, the Planck satellite data suggest a higher normalization of matter perturbations than local measurements of galaxy clusters. Second, the expansion rate of the Universe today, H0, 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 better concordance as well. For our fiducial data set combination, with statistical errors for clusters, a model with a massive sterile neutrino shows 3.5σ evidence for a nonzero 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--of interest for short baseline and reactor anomalies--is well within the allowed range. We caution that (i) unknown astrophysical systematic errors in any of the data sets could weaken this conclusion, but they would need to be several times the known errors to eliminate the tensions entirely; (ii) the results we find are at some variance with analyses that do not include cluster measurements; and (iii) some tension remains among the data sets even when new neutrino physics is included.

Light sterile neutrinos in cosmology and short-baseline oscillation experiments

“…Hence, the inclusion of LGC data in the cosmological fits favors the existence of a sterile neutrino with a mass of the order of that required by SBL data, which is at least partially thermalized in the early Universe [12]. The results of our CMB+H 0 +BAO+LGC fit given in 0.0 0.5 1.0 1.5 2.0 2.5 3.0…”

“…As discussed in Ref. [12], the measured amount of clustering of galaxies [62,63] is smaller than that obtained by evolving the primordial 7 Possible ways of solving this tension have been discussed recently, but before the Planck data release, in Refs. [65][66][67].…”

“…As discussed in Ref. [12], the value of σ 8 and the amount of clustering of galaxies can be lowered by adding to the ΛCDM cosmological model hot dark matter in the form of sterile neutrinos with eVscale masses 8 . The free-streaming of these sterile neutrinos suppresses the growth of structures which are smaller than the free-streaming length, leading to a suppression of σ 8 with respect to the ΛCDM approximate relation σ 8 ∝ Ω 0.563 m .…”

“…The recent results of the Planck experiment [1,2] generated lively discussions [3][4][5][6][7][8][9][10][11][12][13][14] on the value of the effective number of relativistic degrees of freedom N eff before photon decoupling (see [15][16][17]), which gives the energy density of radiation ρ R through the relation ρ R = 1 + 7 8 4 11…”

Dark matter indirect detection signals and the nature of neutrinos in the supersymmetricU(1)B−Lextension of the standard model

“…The present observational bound on ∆N eff (≡ N eff − N eff,SM ) from Planck+WMAP9+ACT+SPT+BAO+HST at 2σ is ∆N eff = 0.48 +0.48 −0.45 [37], which implies that ∆N eff = 0.96 at 2σ.The value of N eff depends on Hubble constant where the Planck data and HST measurements differ [38]. The reconciliation can occur using a non-zero ∆N eff [39]. The tension in the CMB tensor polarization measurement between the recent BICEP2 [40] and Planck data can also be reconciled with ∆N eff =0.81±0.25 at more than 3σ confidence level in a joint analysis [41], strongly disfavoring ∆N eff = 0.…”