198 research outputs found
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
Production Rate of Second KK Gauge Bosons in UED Models at LHC
We calculate the production rates of the second Kaluza-Klein (KK) photon
and Z boson at the LHC including all significant
processes in the minimal universal extra dimension (MUED) model. For
discrimination of the MUED model from other TeV scale models in hadron collider
experiments, and play a crucial role. In order to
discuss the discrimination and calculate their production rates, we derive
effective Lagrangian containing KK number violating operators. We show that KK
number violating processes are extremely important for the compactification
scale larger than 800 GeV. We find that, with an integrated luminosity of 100
fb, and are produced 10 - 10 for the
compactification scale between 400 GeV and 2000 GeV.Comment: To appear in the proceedings of Particle Physics, Astrophysics and
Quantum Field Theory: 75 Years since Solvay, Nanyang Executive Center,
Singapore, 27-29 Nov 200
Relic abundance of dark matter in universal extra dimension models with right-handed neutrinos
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 has. The first KK particle of the right-handed neutrino
is a candidate for dark matter in this framework, and its relic abundance is
determined by three processes, (1) the decay of the KK photon into the first KK
right-handed neutrino in the late universe, (2) production of the first KK
right-handed neutrino from the thermal bath in the early universe, and (3) the
decay of higher KK right-handed neutrinos into the first KK right-handed
neutrino in the late universe. When ordinary neutrino masses are large enough
such as the degenerate mass spectrum case, the last process contribute to the
abundance significantly, even if the reheating temperature is low. 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: added references, changed figure 3 and figure
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