52 research outputs found
The Low-Energy Theorem of Pion Photoproduction in Soliton Models of the Nucleon
We derive an analytic expression for the Kroll-Ruderman amplitude up to the
order 1/N_C for general Skyrme-type models of the nucleon. Due to the
degeneracy of intermediate N- and Delta-states we find deviations from the
standard low-energy theorem for the photoproduction of neutral pions.Comment: 17 pages, LATEX, SI-93-TP3S
Radiative Tau Decays with One Pseudoscalar Meson
We have calculated the decay . We present
the photon energy spectrum, the meson-photon invariant mass spectrum and the
integrated rate as a function of a photon energy cut or an invariant mass cut.
Both the internal bremsstrahlung and the structure dependent radiation have
been taken into account. To this aim we have parametrized the form factors
and , which determine the structure dependent radiation. Observables
especially suited for the measurement of the structure dependent form factors
are found and implications on the width of the discussed.Comment: p.20, TTP93-1, LaTe
Short and Long Distance Effects in the Decay
We calculate the radiative corrections to the decays and
\pi \to l \nu_\l, where the meson is or and the lepton is
or . We perform a complete calculation, which includes internal
bremsstrahlung and structure dependent radiation in the radiative decays and
point meson, hadronic structure dependent and short distance contributions in
the virtual corrections. Our result for the radiative correction to the ratio
is
\delta R_{\tau/\pi} = \left(0.16_{\T - 0.14}^{\T+0.09}\right) \%. For the
ratio , we
obtain \delta R_{\tau/K } = \left(0.90_{\T - 0.26}^{\T + 0.17}\right) \%. For
completeness we have also calculated the ratio of the electronic and muonic
decay modes of the pion.Comment: 39 pages, Latex [19 figures, not included]: A complete postscript
file, including figures, is available via anonymous ftp at
ttpux2.physik.uni-karlsruhe.de (129.13.102.139) as /pub/ttp94-05/ttp94-05.ps,
Local preprint# TTP94-5. Revised version: In the previous version of this
paper we used a relative sign between internal bremsstrahlung and
the structure dependent radiation. However, as explained in TTP93-1A
(hep-ph/940538), we now believe that is the physical choic
Pion photo- and electroproduction and the partially-conserved axial current
The relevance of the axial current for pion production processes off the
nucleon with real or virtual photons is revisited. Employing the hypothesis of
a partially conserved axial current (PCAC), it is shown that, when all of the
relevant contributions are taken into account, PCAC does not provide any
additional constraint for threshold production processes that goes beyond the
Goldberger-Treiman relation. In particular, it is shown that pion
electroproduction processes at threshold cannot be used to extract any
information regarding the weak axial form factor. The relationships found in
previous investigations are seen to be an accident of the approximations
usually made in this context.Comment: 4 pages, 3 figures; typos corrected; references updated; some
rewording; conclusions unchange
A dispersion theoretical approach to the threshold amplitudes of pion photoproduction
We give predictions for the partial wave amplitudes of pion photoproduction
near threshold by means of dispersion relations at fixed t. The free parameters
of this approach are determined by a fit to experimental data in the energy
range 160 MeV 420 MeV. The observables near threshold are
found to be rather sensitive to the amplitudes in the resonance region, in
particular to the (1232) and (1440). We obtain a good agreement
with the existing threshold data for both charged and neutral pion production.
Our predictions also agree well with the results of chiral perturbation theory,
except for neutral pion production off the neutron.Comment: 16 pages LATEX including 4 postscript figure
About estimations of an one-photon background in neutrino oscillation experiments at low neutrino energies
The possible sources of one-photon radiation as background for quasi-elastic
reaction nu_mu+n to mu^-+p are considered. The ones are relevant in experiments
on determination of oscillation parameters at low neutrino energies (E_nu^lab~1
GeV). The estimation for the cross section of reaction nu_mu+n to mu^-+p+gamma
is given at E_nu^lab=0.7 GeV as 0.65% from the corresponding cross section of
quasi-elastic reaction.Comment: 17 pages, 10 figure
Meson photoproduction at threshold in three flavor soliton models
In Skyrme-type models, the leading term of the low-energy photoproduction
amplitude is identical to the standard expression and independent of the number
of flavors considered, but subleading terms are not.Comment: 8 pages, LaTeX, no figure
Threshold Pion Electroproduction in Chiral Perturbation Theory
Electroproduction of pions on the nucleon near the threshold is analyzed
within the framework of baryon chiral perturbation theory. We give a thorough
discussion of the low--energy theorems related to charged and neutral
electropionproduction. It is shown how the axial radius of the nucleon can be
related to the S--wave multipoles and . The chiral
perturbation theory calculations of the reaction
are found to be in good agreement with the recent near threshold data. We also
discuss the influence of some isospin--breaking effects in this channel. For
future experimental tests of the underlying chiral dynamics, extensive
predictions of differential cross sections and multipole amplitudes are
presented.Comment: 44pp, TeX, 15 figures available upon request, BUTP-93/23 and CRN
93-4
An Isobaric Model for Kaon photoproduction
The kaon photoproduction is analyzed up to =2.0 GeV by
using an isobaric model based on effective Lagrangians and by taking a cross
symmetry into account. Both {\it pseudovector} and {\it pseudoscalar} couplings
for kaon-baryon-baryon (baryon spin=1/2) interactions are considered with form
factors. A vector meson(), an axial vector meson(),
nucleon resonances(), and hyperon resonances() are treated as
participating particles. By determining unknown coupling constants through a
systematic fitting of the differential cross section, the total cross section,
the single polarization observable, and the radiative kaon capture branching
ratio to their experimental data, we find out a simple model which reproduces
all the experimental data well.Comment: 48 pages, 7 figure
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