1,536 research outputs found
Nonperturbative corrections to moments of the decay B -> X_s l^+ l^-
We study nonperturbative corrections to the inclusive rare decay B -> X_s l^+
l^- by performing an operator product expansion (OPE) to O(1/m_b^3). The values
of the matrix elements entering at this order are unknown and introduce
uncertainties into physical quantities. We study uncertainties introduced into
the partially integrated rate, moments of the hadronic spectrum, as well as the
forward-backward asymmetry. We find that for large dilepton invariant mass q^2
> M_{\psi'}^2 these uncertainties are large. We also assess the possibility of
extracting the HQET parameters \lambda_1 and \bar{\Lambda} using data from this
process.Comment: 24 pages, revtex, 4 figures, added an appendix with details, results
unchange
Two-Phased Intra-Cluster Medium in the Centaurus Cluster of Galaxies
ASCA and ROSAT data of the Centaurus cluster were analyzed. A central excess
in the radial brightness profile is found in the hard energy band up to 10keV.
This requires a deeper central potential than a King-type one. A double-beta
brightness distribution gives a good account of the data. A deprojected energy
spectrum within a spherical region of radius 30 kpc at the cluster center
indicates that the ICM cannot be isothermal there. Simultaneous fitting of the
three (PSPC, GIS, and SIS) energy spectra extracted from the central 3' region
showed that a two-temperature model that has temperatures of 1.4keV and 4.4keV
and a common metallicity of 1.0 solar with the Galactic absorption gives the
best description to the spectra. A cooling-flow spectral model did not give
satisfactory fit. A 3-dimensional cluster model incorporating the two-phase
picture, the double-beta brightness distribution, and the central metallicity
increase reproduced the overall ASCA and ROSAT data successfully. The derived
spatial distribution of the dark matter deviates from a King-type profile
exhibiting a central excess, which is consistent with the Navvaro-Frenk-White
model. The iron is revealed to be more widely spread than stars, which may have
been caused by energetic supernovae and the motion of the cD galaxy. Since the
derived characteristics of the cool phase including the temperature, angular
extent, gas mass, and metallicity, are on a smooth extension of those of
inter-stellar medium (ISM) of elliptical galaxies, the cool phase can be
regarded as the ISM associated with the cD galaxy. The cool-phase X-ray
emission is presumably sustained by energies dissipated by infalling mass to
the cD galaxy in the course of cluster evolution.Comment: accepted for publication in Ap
Prospects for future very high-energy gamma-ray sky survey: impact of secondary gamma rays
Very high-energy gamma-ray measurements of distant blazars can be well
explained by secondary gamma rays emitted by cascades induced by
ultra-high-energy cosmic rays. The secondary gamma rays will enable one to
detect a large number of blazars with future ground based gamma-ray telescopes
such as Cherenkov Telescope Array (CTA). We show that the secondary emission
process will allow CTA to detect 100, 130, 150, 87, and 8 blazars above 30 GeV,
100 GeV, 300 GeV, 1 TeV, and 10 TeV, respectively, up to assuming the
intergalactic magnetic field (IGMF) strength G and an unbiased all
sky survey with 0.5 hr exposure at each Field of View, where total observing
time is hr. These numbers will be 79, 96, 110, 63, and 6 up to
in the case of G. This large statistics of sources will
be a clear evidence of the secondary gamma-ray scenarios and a new key to
studying the IGMF statistically. We also find that a wider and shallower survey
is favored to detect more and higher redshift sources even if we take into
account secondary gamma rays.Comment: 8 pages, 3 figures, accepted for publication in Astroparticle Physic
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