36,038 research outputs found
Comparison of techniques to reconstruct VHE gamma-ray showers from multiple stereoscopic Cherenkov images
For air showers observed simultaneously by more than two imaging atmospheric
Cherenkov telescopes, the shower geometry is overconstrained by the images and
image information should be combined taking into account the quality of the
images. Different algorithms are discussed and tested experimentally using data
obtained from observations of Mkn 501 with the HEGRA IACT system. Most of these
algorithms provide an estimate of the accuracy of the reconstruction of shower
geometry on an event-by-event basis, allowing, e.g., to select higher-quality
subsamples for precision measurements.Comment: 14 Pages, 6 figures, Late
Symmetry breaking: A tool to unveil the topology of chaotic scattering with three degrees of freedom
We shall use symmetry breaking as a tool to attack the problem of identifying
the topology of chaotic scatteruing with more then two degrees of freedom.
specifically we discuss the structure of the homoclinic/heteroclinic tangle and
the connection between the chaotic invariant set, the scattering functions and
the singularities in the cross section for a class of scattering systems with
one open and two closed degrees of freedom.Comment: 13 pages and 8 figure
The intrinsic strangeness and charm of the nucleon using improved staggered fermions
We calculate the intrinsic strangeness of the nucleon, - ,
using the MILC library of improved staggered gauge configurations using the
Asqtad and HISQ actions. Additionally, we present a preliminary calculation of
the intrinsic charm of the nucleon using the HISQ action with dynamical charm.
The calculation is done with a method which incorporates features of both
commonly-used methods, the direct evaluation of the three-point function and
the application of the Feynman- Hellman theorem. We present an improvement on
this method that further reduces the statistical error, and check the result
from this hybrid method against the other two methods and find that they are
consistent. The values for and found here, together with
perturbative results for heavy quarks, show that dark matter scattering through
Higgs-like exchange receives roughly equal contributions from all heavy quark
flavors.Comment: 17 pages, 14 figure
Top quark forward-backward asymmetry and charge asymmetry in left-right twin Higgs model
In order to explain the Tevatron anomaly of the top quark forward-backward
asymmetry in the left-right twin Higgs model, we choose to give up
the lightest neutral particle of field as a stable dark matter
candidate. Then a new Yukawa interaction for is allowed, which can be
free from the constraint of same-sign top pair production and contribute
sizably to . Considering the constraints from the production rates of
the top pair (), the top decay rates and invariant mass
distribution, we find that this model with such new Yukawa interaction can
explain measured at the Tevatron while satisfying the charge
asymmetry measured at the LHC.Moreover, this model predicts a
strongly correlation between at the LHC and at the
Tevatron, i.e., increases as increases.Comment: 17 pages, 9 figures; matches the published versio
Black hole particle emission in higher-dimensional spacetimes
In models with extra dimensions, a black hole evaporates both in the bulk and
on the visible brane, where standard model fields live. The exact emissivities
of each particle species are needed to determine how the black hole decay
proceeds. We compute and discuss the absorption cross-sections, the relative
emissivities and the total power output of all known fields in the evaporation
phase. Graviton emissivity is highly enhanced as the spacetime dimensionality
increases. Therefore, a black hole loses a significant fraction of its mass in
the bulk. This result has important consequences for the phenomenology of black
holes in models with extra dimensions and black hole detection in particle
colliders.Comment: 4 pages, RevTeX 4. v3: Misprints in Tables correcte
Spin/Orbital Pattern-Dependent Polaron Absorption in Nd(1-x)Sr(x)MnO3
We investigated optical properties of Nd(1-x)Sr(x)MnO3 (x= 0.40, 0.50, 0.55,
and 0.65) single crystals. In the spin/orbital disordered state, their
conductivity spectra look quite similar, and the strength of the mid-infrared
absorption peak is proportional to x(1-x) consistent with the polaron picture.
As temperature lowers, the Nd(1-x)Sr(x)MnO3 samples enter into various
spin/orbital ordered states, whose optical responses are quite different. These
optical responses can be explained by the spin/orbital ordering
pattern-dependent polaron hopping.Comment: 3 figures (gzipped
Optical Studies of a Layered Manganite La_{1.2}Sr_{1.8}Mn_2O_7 : Polaron Correlation Effect
Optical conductivity spectra of a cleaved ab-plane of a
La_{1.2}Sr_{1.8}Mn_2O_7 single crystal exhibit a small polaron absorption band
in the mid-infrared region at overall temperatures. With decreasing temperature
(T) to Curie temperature (T_C), the center frequency of the small polaron band
moves to a higher frequency, resulting in a gap-like feature, and that it
collapses to a lower frequency below T_C. Interestingly, with decreasing T, the
stretching phonon mode hardens above T_C and softens below T_C. These
concurring changes of lattice and electronic structure indicate that short
range polaron correlation exist above T_C but disappear with a magnetic
ordering.Comment: 4 pages including 5 figures. submitted to Phys. Rev.
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