4,124 research outputs found
Cosmic e^\pm, \bar p, \gamma and neutrino rays in leptocentric dark matter models
Dark matter annihilation is one of the leading explanations for the recently
observed excesses in cosmic rays by PAMELA, ATIC, FERMI-LAT and HESS.
Any dark matter annihilation model proposed to explain these data must also
explain the fact that PAMELA data show excesses only in spectrum but
not in anti-proton. It is interesting to ask whether the annihilation mode into
anti-proton is completely disallowed or only suppressed at low energies. Most
models proposed have negligible anti-protons in all energy ranges. We show that
the leptocentric dark matter model can explain the
excesses with suppressed anti-proton mode at low energies, but at higher
energies there are sizable anti-proton excesses. Near future data from PAMELA
and AMS can provide crucial test for this type of models. Cosmic ray
data can further rule out some of the models. We also show that this model has
interesting cosmic neutrino signatures.Comment: Latex 20 pages and five figures. References adde
Quasi-two-body decays in the perturbative QCD approach
In this paper, we calculated the branching ratios of the quasi-two-body
decays
by employing the perturbative QCD (PQCD) approach. The contributions from the
-wave resonances , and were taken into
account. The two-pion distribution amplitude is
parameterized by the vector current time-like form factor to study
the considered decay modes. We found that (a) the PQCD predictions for the
branching ratios of the considered quasi-two-body decays are in the order of
, while the two-body decay rates are extracted from those for the
corresponding quasi-two-body decays; (b) the whole pattern of the pion form
factor-squared measured by the BABAR Collaboration could be
understood based on our theoretical results; (c) the general expectation based
on the similarity between and
decays are confirmed: is consistent with the measured
within errors; and (d) new ratios
and among the branching ratios of the
considered decay modes are defined and could be tested by future experiments.Comment: 10 pages, 3 figure
Quasi-two-body decays in the perturbative QCD approach
We study the quasi-two-body decays by employing
the perturbative QCD approach. The two-meson distribution amplitudes
\Phi_{K\pi}^{\text{P-wave}} are adopted to describe the final state
interactions of the kaon-pion pair in the resonance region. The resonance line
shape for the -wave component in the time-like form factor
is parameterized by the relativistic Breit-Wigner function. For
most considered decay modes, the theoretical predictions for their branching
ratios are consistent with currently available experimental measurements within
errors. We also disscuss some ratios of the branching fractions of the
concerned decay processes. More precise data from LHCb and Belle-II are
expected to test our predictions.Comment: 10 pages, 3 figures and 2 tables.To be published in EPJ
Pyrogen reaction and conversion of sustained ventricular tachycardia to sinus rhythm: two case reports
INTRODUCTION: Pyrogen reaction is a side effect of intravenous infusion of solution on body; sustained ventricular tachycardia is a serious arrhythmia, no relationship between them has been reported before. CASE PRESENTATION: Two patients with sustained ventricular tachycardia refractory to lidocaine happened to have pyrogen reaction. The sustained ventricular tachycardia was converted to sinus rhythm after the pyrogen reaction. CONCLUSION: The conversion of sustained ventricular tachycardia might be related to pyrogen reaction. The effects of pyrogen reaction on sustained ventricular tachycardia need further research
Superposition coded modulation with peak-power limitation
We apply clipping to superposition coded modulation (SCM) systems to reduce the peak-to-average power ratio (PAPR) of the transmitted signal. The impact on performance is investigated by evaluating the mutual information driven by the induced peak-power-limited input signals. It is shown that the rate loss is marginal for moderate clipping thresholds if optimal encoding/decoding is used. This fact is confirmed in examples where capacityapproaching component codes are used together with the maximum a posteriori probability (MAP) detection. In order to reduce the detection complexity of SCM with a large number of layers, we develop a suboptimal soft compensation (SC) method that is combined with soft-input soft-output (SISO) decoding algorithms in an iterative manner. A variety of simulation results for additive white Gaussian noise (AWGN) and fading channels are presented. It is shown that with the proposed method, the effect of clipping can be efficiently compensated and a good tradeoff between PAPR and bit-error rate (BER) can be achieved. Comparisons with other coded modulation schemes demonstrate that SCM offers significant advantages for high-rate transmissions over fading channels
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