49 research outputs found
Dark matter component decaying after recombination: lensing constraints with Planck data
It has been recently suggested~\cite{Berezhiani:2015yta} that emerging
tension between cosmological parameter values derived in high-redshift (CMB
anisotropy) and low-redshift (cluster counts, Hubble constant) measurements can
be reconciled in a model which contains subdominant fraction of dark matter
decaying after recombination. We check the model against the CMB Planck data.
We find that lensing of the CMB anisotropies by the large-scale structure gives
strong extra constraints on this model, limiting the fraction as at
2\, confidence level. However, investigating the combined data set of
CMB and conflicting low- measurements, we obtain that the model with
\% exhibits better fit (by 1.5-3\, depending on the
lensing priors) compared to that of the concordance CDM cosmological
model.Comment: 5 pages, 4 figures; v2: journal version, pages++, figures+
Induced resonance makes light sterile neutrino Dark Matter cool
We describe two new generation mechanisms for Dark Matter composed of sterile
neutrinos with keV mass. The model contains a light scalar field
which coherently oscillates in the early Universe and modulates the Majorana
mass of the sterile neutrino. In a region of model parameter space, the
oscillations between active and sterile neutrinos are resonantly enhanced. This
mechanism allows us to produce sterile neutrino DM with small mixing angle with
active neutrinos, thus evading the X-ray constraints. At the same time the
spectrum of produced DM is much cooler, than in the case of ordinary
oscillations in plasma, opening a window of lower mass DM, which is otherwise
forbidden by structure formation considerations. In other regions of the model
parameter space, where the resonance does not appear, another mechanism can
operate: large field suppresses the active-sterile oscillations, but instead
sterile neutrinos are produced by the oscillating scalar field when the
effective fermion mass crosses zero. In this case DM component is cold, and
even 1 keV neutrino is consistent with the cosmic structure formation.Comment: 6 pages, 4 figures, PRD accepted versio
Cosmology based on f(R) gravity with O(1) eV sterile neutrino
© 2015 IOP Publishing Ltd and Sissa Medialab srl. We address the cosmological role of an additional (1) eV sterile neutrino in modified gravity models. We confront the present cosmological data with predictions of the FLRW cosmological model based on a variant of f(R) modified gravity proposed by one of the authors previously. This viable cosmological model which deviation from general relativity with a cosmological constant Λ decreases as R-2n for large, but not too large values of the Ricci scalar R (while no Λ is introduced by hand at small R) provides an alternative explanation of present dark energy and the accelerated expansion of the Universe (the case n=2 is considered in the paper). Various up-to-date cosmological data sets exploited include measurements of the cosmic microwave background (CMB) anisotropy, the CMB lensing potential, the baryon acoustic oscillations (BAO), the cluster mass function and the Hubble constant. We find that the CMB+BAO constraints strongly restrict the sum of neutrino masses from above. This excludes values of the model parameter λ∼ 1 for which distinctive cosmological features of the model are mostly pronounced as compared to the ΛCDM model, since then free streaming damping of perturbations due to neutrino rest masses is not sufficient to compensate their extra growth occurring in f(R) modified gravity. Thus, in the gravity sector we obtain λ>8.2 (2σ) with the account of systematic uncertainties in galaxy cluster mass function measurements and λ>9.4 (2σ) without them. At the same time in the latter case we find for the sterile neutrino mass 0.47 eV ν, sterile ν, sterile ν, sterile ≈ 1.5 eV motivated by various anomalies in neutrino oscillation experiments would favor cosmology based on f(R) gravity rather than the ΛCDM model