3,466 research outputs found
Weak hyperon decays in heavy baryon chiral perturbation theory: Renormalization and applications
The complete renormalization of the weak Lagrangian to chiral order q^2 in
heavy baryon chiral perturbation theory is performed using heat kernel
techniques. The results are compared with divergences appearing in the
calculation of Feynman graphs for the nonleptonic hyperon decay Lambda -> p
pi^- and an estimate for the size of the counterterm contributions to the
s-wave amplitudes in nonleptonic hyperon decays is given.Comment: 21 pages, 2 figure
A perturbative treatment for the energy levels of neutral atoms
Energy levels of neutral atoms have been re-examined by applying an
alternative perturbative scheme in solving the Schrodinger equation for the
Yukawa potential model with a modified screening parameter. The predicted shell
binding energies are found to be quite accurate over the entire range of the
atomic number up to 84 and compare very well with those obtained within the
framework of hyper-virial-Pade scheme and the method of shifted large-N
expansion. It is observed that the new perturbative method may also be applied
to the other areas of atomic physics.Comment: 18 page
A sum rule approach to the violation of Dashen's theorem
A classic sum rule by Das et al. is extended to seven of the low-energy
constants , introduced by Urech, which parameterize electromagnetic
corrections at chiral order . Using the spurion formalism, a simple
convolution representation is shown to hold and the structure in terms of the
chiral renormalization scale, the QCD renormalization scale and the QED gauge
parameter is displayed. The role of the resonances is studied as providing
rational interpolants to relevant QCD n-point functions in the euclidian
domain. A variety of asymptotic constraints must be implemented which have
phenomenological consequences. A current assumption concerning the dominance of
the lowest-lying resonances is shown clearly to fail in some cases.Comment: A few corrections and improvements made, the list of references is
more complet
Low Energy Constants from High Energy Theorems
New constraints on resonance saturation in chiral perturbation theory are
investigated. These constraints arise because each consistent saturation scheme
must map to a representation of the full QCD chiral symmetry group. The
low-energy constants of chiral perturbation theory are then related by a set of
mixing angles. It is shown that vector meson dominance is a consequence of the
fact that nature has chosen the lowest-dimensional nontrivial chiral
representation. It is further shown that chiral symmetry places an upper bound
on the mass of the lightest scalar in the hadron spectrum.Comment: 11 pages TeX and mtexsis.te
Baryon axial currents
The baryon axial currents are calculated at one-loop order in heavy baryon
chiral perturbation theory by employing both a cutoff and dimensional
regularization. Data from the semileptonic baryon decays is used to perform a
least-squares fit to the two axial couplings D and F of the effective
Lagrangian. Predictions for the momentum dependent axial form factors are made
and the two different regularization schemes are compared. We also include the
spin-3/2 decuplet in the effective theory.Comment: 27 pages, 8 figure
Isospin breaking in the vector current of the nucleon
Extraction of the nucleon's strange form factors from experimental data
requires a quantitative understanding of the unavoidable contamination from
isospin violation. A number of authors have addressed this issue during the
past decade, and their work is reviewed here. The predictions from early models
are largely consistent with recent results that rely as much as possible on
input from QCD symmetries and related experimental data. The resulting bounds
on isospin violation are sufficiently precise to be of value to on-going
experimental and theoretical studies of the nucleon's strange form factors.Comment: 5 pages, 3 figures. Presented at the International Workshop "From
Parity Violation to Hadronic Structure and more...", Milos, Greece, 16-20 May
2006. Version 2 is only to update Refs. [21] and [25
One loop corrections to quantum hadrodynamics with vector mesons
The renormalized elastic scattering amplitude to one loop is
calculated in the chiral limit in the model and in a Quantum
Hadrodynamic model (QHD-III) with vector mesons. It is argued that QHD-III
reduces to the linear model in the limit that the vector meson masses
become large. The pion decay constant is also calculated to 1-loop in the
model, and at tree level in QHD-III; it is shown that the coefficient
of the tree level term in the scattering amplitude equals . The
1-loop correction of in QHD-III violates strong isospin current
conservation. Thus,it is concluded that QHD-III can, at best, only describe the
strongly interacting nuclear sector.Comment: 6 page
Tensor meson exchange at low energies
We complete the analysis of meson resonance contributions to chiral
low-energy constants of O(p^4) by including all quark-antiquark bound states
with orbital angular momentum less or equal to one. Different tensor meson
Lagrangians used in previous work are shown to produce the same final results
for the low-energy constants once QCD short-distance constraints are properly
implemented. We also discuss the possible relevance of axial-vector mesons with
odd C-parity.Comment: 20 pages, comparison with previous work updated, typos removed,
results unchanged, version to appear in EPJ
Final State Interactions and CP Violation in
Using chiral perturbation theory we calculate the imaginary parts of the form factors that arise from and
rescattering. We discuss their influence on CP violating variables in .Comment: ; 12 pages, 2 figures, TeX format; uses epsf.tex, tables.tex, and
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