193 research outputs found
The Cosmological Energy Density of Neutrinos from Oscillation Measurements
The emerging structure of the neutrino mass matrix, when combined with the
primordial element abundances, places the most stringent constraint on the
flavor asymmetries in the cosmological neutrino background and therefore its
energy density. I review the mechanism of synchronized neutrino oscillations in
the an early universe with degenerate (asymmetric) neutrino and antineutrino
densities and the implications of refined measurements of neutrino parameters.Comment: 4 pages, Proceedings of NuFact 03, 5th International Workshop on
Neutrino Factories & Superbeams, 5-11 June 2003, Columbia University, New
Yor
Resonantly-Produced 7 keV Sterile Neutrino Dark Matter Models and the Properties of Milky Way Satellites
Sterile neutrinos produced through a resonant Shi-Fuller mechanism are
arguably the simplest model for a dark matter interpretation origin of the
recent unidentified X-ray line seen toward a number of objects harboring dark
matter. Here, I calculate the exact parameters required in this mechanism to
produce the signal. The suppression of small scale structure predicted by these
models is consistent with Local Group and high- galaxy count constraints.
Very significantly, the parameters necessary in these models to produce the
full dark matter density fulfill previously determined requirements to
successfully match the Milky Way Galaxy's total satellite abundance, the
satellites' radial distribution and their mass density profile, or "too big to
fail problem." I also discuss how further precision determinations of the
detailed properties of the candidate sterile neutrino dark matter can probe the
nature of the quark-hadron transition, which takes place during the dark matter
production.Comment: 5 pages, 3 figures. v3: discussion added, matches version accepted to
Phys. Rev. Let
Sterile neutrinos in cosmology
Sterile neutrinos are natural extensions to the standard model of particle
physics in neutrino mass generation mechanisms. If they are relatively light,
less than approximately 10 keV, they can alter cosmology significantly, from
the early Universe to the matter and radiation energy density today. Here, we
review the cosmological role such light sterile neutrinos can play from the
early Universe, including production of keV-scale sterile neutrinos as dark
matter candidates, and dynamics of light eV-scale sterile neutrinos during the
weakly-coupled active neutrino era. We review proposed signatures of light
sterile neutrinos in cosmic microwave background and large scale structure
data. We also discuss keV-scale sterile neutrino dark matter decay signatures
in X-ray observations, including recent candidate 3.5 keV X-ray line
detections consistent with the decay of a 7 keV sterile neutrino dark
matter particle.Comment: Accepted version of an invited review for Physics Reports. 33 pages,
7 figures, approximately 16,000 words; v3: expanded discussion of low
reheating temperature universe models with a new figure, large scale
structure effects, scalar decay model
Comment on "Joint Anisotropy and Source Count Constraints on the Contribution of Blazars to the Diffuse Gamma-Ray Background"
We show the conclusions claimed in the manuscript arXiv:1202.5309v1 by Cuoco,
Komatsu and Siegal-Gaskins (CKS) are not generally valid. The results in CKS
are based on a number of simplifying assumptions regarding the source
population below the detection threshold and the threshold flux itself, and do
not apply to many physical models of the blazar population. Physical blazar
population models that match the measured source counts above the observational
threshold can account for 60% of the diffuse gamma-ray background intensity
between 1-10 GeV, while the assumptions in CKS limit the intensity to <30%. The
shortcomings of the model considered in CKS arise from an over-simplified
blazar source model. A number of the simplifying assumptions are unjustified,
including: first, the adoption of an assumed power-law source-count
distribution, dN/dS, to arbitrary low source fluxes, which is not exhibited in
physical models of the blazar population; and, second, the lack of blazar
spectral information in calculating the anisotropy of unresolved gamma-ray
blazar emission. We also show that the calculation of the unresolved blazars'
anisotropy is very sensitive to the spectral distribution of the unresolved
blazars through the adopted source resolution threshold value, and must be
taken into account in an accurate anisotropy calculation.Comment: 4 pages, 1 figure, comment on arXiv:1202.5309v
Bulk QCD Thermodynamics and Sterile Neutrino Dark Matter
We point out that the relic densities of singlet (sterile) neutrinos of
interest in viable warm and cold dark matter scenarios, depend on the
characteristics of the QCD transition in the early universe. In the most
promising of these dark matter scenarios the production of the singlets occurs
at or near the QCD transition. Since production of the singlets, their
dilution, and the disappearance of weak scatterers occur simultaneously, we
calculate these processes contemporaneously to obtain accurate predictions of
relic sterile neutrino mass density. Therefore, a determination of the mass and
superweak mixing of the singlet neutrino through, for example, its radiative
decay, along with a determination of its contribution to the critical density,
can provide insight into the finite-temperature QCD transition.Comment: 7 pages, 4 figures, to match version in Phys. Rev.
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