3,302 research outputs found
Observation of Electrons above 100 GeV with the BETS Detector Using Long-Duration Balloon in Antarctica
Enhancement of the annihilation of dark matter in a radiative seesaw model
The radiative seesaw model with an inert doublet has been shown to be
attractive from a viewpoint of both neutrino masses and cold dark matter.
However, if we apply this model to the explanation of the positron excess in
the cosmic ray observed by PAMELA, a huge boost factor is required although it
can be automatically explained that no anti-proton excess has been observed
there. We consider an extension of the model to enhance the thermally averaged
annihilation cross section without changing the features of the model favored
by both the neutrino oscillation and the relic abundance of dark matter. It is
shown that the data of PAMELA and Fermi-LAT can be well explained in this
extended model. Constraints from gamma ray observations are also discussed.Comment: 28 pages, 5 figures, final version for publicatio
Thermal-Fluid Flow Transport Phenomenon over Slot-Perforated Flat Plates Placed in Narrow Channel
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76151/1/AIAA-25872-119.pd
Observation of an energetic radiation burst from mountain-top thunderclouds
During thunderstorms on 2008 September 20, a simultaneous detection of gamma
rays and electrons was made at a mountain observatory in Japan located 2770 m
above sea level. Both emissions, lasting 90 seconds, were associated with
thunderclouds rather than lightning. The photon spectrum, extending to 10 MeV,
can be interpreted as consisting of bremsstrahlung gamma rays arriving from a
source which is 60 - 130 m in distance at 90% confidence level. The observed
electrons are likely to be dominated by a primary population escaping from an
acceleration region in the clouds.Comment: 12 pages, 3 figures, accepted for publication in Physical Review
Letter
Perturbations of global monopoles as a black hole's hair
We study the stability of a spherically symmetric black hole with a global
monopole hair. Asymptotically the spacetime is flat but has a deficit solid
angle which depends on the vacuum expectation value of the scalar field. When
the vacuum expectation value is larger than a certain critical value, this
spacetime has a cosmological event horizon. We investigate the stability of
these solutions against the spherical and polar perturbations and confirm that
the global monopole hair is stable in both cases. Although we consider some
particular modes in the polar case, our analysis suggests the conservation of
the "topological charge" in the presence of the event horizons and violation of
black hole no-hair conjecture in asymptotically non-flat spacetime.Comment: 11 pages, 2 figures, some descriptions were improve
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