2,974 research outputs found
Development of a systematic approach to conversion of the ileoanal pouch into continent ileostomy
Based on practical experience, a systematic approach to conversion of ileal J-pouches into continent ileostomies is developed by defining three types of conversion surgery, each with two subtypes. Type 1 refers to conversion without pouch reconstruction, type 2 to partial pouch reconstruction, and type 3 to complete pouch reconstruction. The subdivisions (a and b) take into account whether the afferent loop of the former pelvic pouch (a) or a higher ileal/jejunal segment of the small intestine (b) is used in conversion and/or reconstruction. The six resulting surgical variants are shown in schematic illustrations with accompanying descriptions of technical details to provide the specialized surgeon with comprehensive technical guidance
Comment on soft-pion emission in DVCS
The soft-pion theorem for pion production in deeply virtual Compton
scattering, derived by Guichon, Mosse and Vanderhaegen, is shown to be
consistent with chiral perturbation theory. Chiral symmetry requires that the
nonsinglet operators corresponding to spin-independent and spin-dependent
parton distributions have the same anomalous dimensions in cases where those
operators are related by chiral transformations. In chiral perturbation theory,
their scale-dependences can thus be absorbed in the coefficents of the
corresponding effective operators, without affecting their chiral structures.Comment: 2 pages, RevTe
Final-sate radiation in electron-positron annihilation into a pion pair
The process of annihilation into a pair with radiation
of a photon is considered. The amplitude of the reaction
consists of the model independent initial-state
radiation (ISR) and model-dependent final-state radiation (FSR). The general
structure of the FSR tensor is constructed from Lorentz covariance, gauge
invariance and discrete symmetries in terms of the three invariant functions.
To calculate these functions we apply Chiral Perturbation Theory (ChPT) with
vector and axial-vector mesons. The contribution of
process to the muon anomalous magnetic moment is evaluated, and results are
compared with the dominant contribution in the framework of a hybrid model,
consisting of VMD and point-like scalar eletrodynamics. The developed approach
allows us also to calculate the charge asymmetry.Comment: 21 pages, 8 figure
Radiative Kaon Decays and Direct CP Violation
It is stressed that a measurement of the electric dipole amplitude for direct
photon emission in \kpm decays through its interference with inner
bremsstrahlung is important for differentiating among various models. Effects
of amplitude CP violation in the radiative decays of the charged kaon are
analyzed in the Standard Model in conjunction with the large approach. We
point out that gluon and electromagnetic penguin contributions to the
CP-violating asymmetry between the Dalitz plots of \kpm are of equal weight.
The magnitude of CP asymmetry ranges from to when the photon energy in the kaon rest frame varies from 50 MeV to
170 MeV.Comment: Latex, 11 pages, ITP-SB-93-36, IP-ASTP-22-9
On the analysis of the pion--nucleon --term: The size of the remainder at the Cheng--Dashen point
We calculate the one--loop contributions of order to the difference
between the on--shell pion--nucleon scattering amplitude
at the Cheng--Dashen point , and
the scalar form factor in the framework of heavy baryon
chiral perturbation theory. We proof that to this order contains
chiral logarithms and therefore it vanishes simply as in the
chiral limit. Numerically, we find as an upper limit MeV.Comment: 7 pp, LaTeX, uses epsf, 1 figure in separate PS fil
One-loop vertex integrals in heavy-particle effective theories
We give a complete analytical computation of three-point one-loop integrals
with one heavy propagator, up to the third tensor rank, for arbitrary values of
external momenta and masses.Comment: 10 pages, Latex, to appear in J. Phys.
FCNC in left-right symmetric theories and constraints on the right-handed scale
We revise the limits on the FCNC higgses in manifestly left-right symmetric
theories. It is shown that the combination of the Kobayashi-Maskawa
CP-violation with the tree level higgs exchange gives very large
contribution to the CP-violating parameter. It leads to the new
strong constraint on the FCNC higgs mass, M>50- 100 TeV, enhanced by factor of
the order . Being addressed to the supersymmetric left-right
models, FCNC problem requires both right-handed scale and supersymmetric mass
parameters be heavier than 50 TeV for . The most relaxed case
corresponds to where right-handed scale can be of the
order of few TeV.Comment: 11 pages, latex, 3 figure
The reaction at threshold in chiral perturbation theory
In the framework of heavy baryon chiral perturbation theory, we give thIn the
framework of heavy baryon chiral perturbation theory, we give the chiral
expansion for the threshold amplitudes and to
quadratic order in the pion mass. The theoretical results agree within one
standard deviation with the empirical values. We also derive a relation between
the two threshold amplitudes of the reaction and the S--wave scattering lengths, and , respectively, to order
. We show that there are uncertainties mostly related to
resonance excitation which make an accurate determination of the
scattering length from the threshold amplitudes at present
very difficult. The situation is different in the isospin two final
state. Here, the chiral series converges and one finds consistent with the one--loop chiral perturbation theory prediction.Comment: 30 pp, LaTeX file, uses epsf, 6 figures (appended), corrections in
sections 5 and 6, conclusions unchange
Aspects of chiral pion-nucleon physics
The next-to-leading order chiral pion-nucleon Lagrangian contains seven
finite low-energy constants. Two can be fixed from the nucleon anomalous
magnetic moments and another one from the quark mass contribution to the
neutron-proton mass splitting. We find a set of nine observables, which to one
loop order do only depend on the remaining four dimension two couplings. These
are then determined from a best fit. We also show that their values can be
understood in terms of resonance exchange related to excitation as
well as vector and scalar meson exchange. In particular, we discuss the role of
the fictitious scalar-isoscalar meson. We also investigate the chiral expansion
of the two P-wave scattering volumes and as well as the
isovector S-wave effective range parameter . The one-loop calculation is
in good agreement with the data. The difference signals chiral
loop effects in the P-waves. The calculated D- and F-wave threshold
parameters compare well with the empirical values.Comment: 19 pp, LaTeX, enlarged and revised version, title changed, minor
corrections in section 4, more detailed discussion in section 5, additional
results in sec. 6 and the appendix, accepted for publication in Nucl. Phys.
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