691 research outputs found
Relic abundance of dark matter in the minimal universal extra dimension model
We investigate the relic abundance of dark matter in the minimal universal
extra dimension model including resonance processes by second Kaluza-Klein (KK)
particles in all coannihilation processes. After including second KK resonance
processes, the relic abundance of dark matter is reduced by about 30%. Thus,
the compactification scale 1/R of the extra dimension consistent with the WMAP
observation is increased by a few hundred GeV. As a result, the cosmologically
allowed compactification scale is 600 GeV < 1/R < 1400 GeV for Lambda R = 20.Comment: 24 pages, 7 figure
Solving cosmological problem in universal extra dimension models by introducing Dirac neutrino
Universal extra dimension (UED) models with right-handed neutrinos are
studied. The introduction of the neutrinos makes us possible not only to
describe Dirac neutrino masses but also to solve the cosmological problem
called the KK graviton problem. This problem is essentially caused by the late
time decay of a KK photon into a KK graviton and a photon, and it distorts the
spectrum of the cosmic microwave background or the diffuse photon. We point out
that, once we introduce right-handed neutrinos to UED models, the KK photon
decays dominantly into neutrinos and does not emit a photon. We also discuss
sub-dominant modes with a photon in the decay quantitatively, and show that
their branching ratios are so small that the spectra are not distorted.Comment: Some discussions are added
The neutrino masses and the change of allowed parameter region in universal extra dimension models
Relic abundance of dark matter is investigated in the framework of universal
extra dimension models with right-handed neutrinos. These models are free from
the serious Kaluza-Klein (KK) graviton problem that the original universal
extra dimension model possesses. The first KK particle of the right-handed
neutrino is a candidate for dark matter in this framework. When ordinary
neutrino masses are large enough such as the degenerate mass spectrum case, the
dark matter relic abundance can change significantly. The scale of the extra
dimension consistent with cosmological observations can be 500 GeV in the
minimal setup of universal extra dimension models with right-handed neutrinos.Comment: 3 pages, to appear in the conference proceedings of TAUP 200
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