1,415 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
Measurements of Antenna Surface for Millimeter-Wave Space Radio Telescope
In the construction of a space radio telescope, it is essential to use
materials with a low noise factor and high mechanical robustness for the
antenna surface. We present the results of measurements of the reflection
performance of two candidates for antenna surface materials for use in a radio
telescope installed in a new millimeter-wave astronomical satellite, ASTRO-G.
To estimate the amount of degradation caused by fluctuations in the thermal
environment in the projected orbit of the satellite, a thermal cycle test was
carried out for two candidates, namely, copper foil carbon fiber reinforced
plastic (CFRP) and aluminum-coated CFRP. At certain points during the thermal
cycle test, the reflection loss of the surfaces was measured precisely by using
a radiometer in the 41-45 GHz band. In both candidates, cracks appeared on the
surface after the thermal cycle test, where the number density of the cracks
increased as the thermal cycle progressed. The reflection loss also increased
in proportion to the number density of the cracks. Nevertheless, the loss of
the copper foil surface met the requirements of ASTRO-G at the end of the
equivalent life, whereas that of the aluminum-coated surface exceeded the
maximal value in the requirement even before the end of the cycle.Comment: 11 pages, 6 figures, accepted for publication in PAS
Recent progress in silica aerogel Cherenkov radiator
In this paper, we present recent progress in the development of hydrophobic
silica aerogel as a Cherenkov radiator. In addition to the conventional method,
the recently developed pin-drying method for producing high-refractive-index
aerogels with high transparency was studied in detail. Optical qualities and
large tile handling for crack-free aerogels were investigated. Sufficient
photons were detected from high-performance aerogels in a beam test.Comment: Proceedings of 2nd International Conference on Technology and
Instrumentation in Particle Physics (TIPP 2011), to be published in Physics
Procedia, 8 pages, 7 figure
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