38,746 research outputs found
Polarization amplitudes in decay beyond the standard model
We use a recent formalism of the weak hadronic reactions to study the helicity amplitudes in decay. This recent formalism maps the transition matrix elements at the
quark level into hadronic matrix elements, and finally writes the weak matrix
elements in terms of easy analytical formulas evaluated by means of an
elaborate angular momentum algebra. The formalism provides directly the
amplitudes for the different spin third components of the vector mesons
involved. We extend the formalism to a general case, with the operator
, that can account for different models
beyond the standard model and study in detail the reaction for the different helicities of the . The results are
shown in terms of the parameter that differs for each model. We find
that is very different for
the different components and in particular the magnitude is very sensitive to the parameter,
which makes the investigation of this magnitude a most welcome initiative to
test different models beyond the standard model.Comment: 20 pages, 6 figures, add some discussion
Helicity amplitudes in decay
We use a recent formalism of the weak hadronic reactions that maps the
transition matrix elements at the quark level into hadronic matrix elements,
evaluated with an elaborate angular momentum algebra that allows finally to
write the weak matrix elements in terms of easy analytical formulas. In
particular they appear explicitly for the different spin third components of
the vector mesons involved. We extend the formalism to a general case, with the
operator , that can accommodate
different models beyond the standard model and study in detail the reaction for the different helicities of the . The results
are shown for each amplitude in terms of the parameter that is
different for each model. We show that is very different for the different components and in
particular the magnitude is very sensitive to the
parameter, which suggest to use this magnitude to test different
models beyond the standard model. We also compare our results with the standard
model and find very similar results, and practically identical at the end point
of .Comment: 25 pages, 10 figure
Two photon couplings of the lightest isoscalars from BELLE data
Amplitude Analysis of two photon production of and ,
using S-matrix constraints and fitting all available data, including the latest
precision results from Belle, yields a single partial wave solution up to 1.4
GeV. The two photon couplings of the , and
are determined from the residues of the resonance poles.Comment: 11 pages, 3 figures, extended for detail
Convergence of Gradient Descent for Low-Rank Matrix Approximation
This paper provides a proof of global convergence of gradient search for low-rank matrix approximation. Such approximations have recently been of interest for large-scale problems, as well as for dictionary learning for sparse signal representations and matrix completion. The proof is based on the interpretation of the problem as an optimization on the Grassmann manifold and Fubiny-Study distance on this space
Spectrum and Duration of Delayed MeV-GeV Emission of Gamma-Ray Bursts in Cosmic Background Radiation Fields
We generally analyze prompt high-energy emission above a few hundreds of GeV
due to synchrotron self-Compton scattering in internal shocks. However, such
photons cannot be detected because they may collide with cosmic infrared
background photons, leading to electron/positron pair production.
Inverse-Compton scattering of the resulting electron/positron pairs off cosmic
microwave background photons will produce delayed MeV-GeV emission, which may
be much stronger than a typical high-energy afterglow in the external shock
model. We expand on the Cheng & Cheng model by deriving the emission spectrum
and duration in the standard fireball shock model. A typical duration of the
emission is ~ 10^3 seconds, and the time-integrated scattered photon spectrum
is nu^{-(p+6)/4}, where p is the index of the electron energy distribution
behind internal shocks. This is slightly harder than the synchrotron photon
spectrum, nu^{-(p+2)/2}. The lower energy property of the scattered photon
spectrum is dependent on the spectral energy distribution of the cosmic
infrared background radiation. Therefore, future observations on such delayed
MeV-GeV emission and the higher-energy spectral cutoff by the Gamma-Ray Large
Area Space Telescope (GLAST) would provide a probe of the cosmic infrared
background radiation.Comment: 5 pages, accepted for publication in Ap
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