905 research outputs found
Cusps in K --> 3 pi decays
The pion mass difference generates a pronounced cusp in K --> 3 pi decays. As
has recently been pointed out by Cabibbo and Isidori, an accurate measurement
of the cusp may allow one to pin down the S-wave pi pi scattering lengths to
high precision. Here, we present and illustrate an effective field theory
framework that allows one to determine the structure of this cusp in a
straightforward manner. The strictures imposed by analyticity and unitarity are
respected automatically.Comment: 14 pages, 3 figures, uses Elsevier styl
Isospin-breaking corrections in the pion-deuteron scattering length
It is shown that isospin-breaking corrections to the pion-deuteron scattering
length can be very large, because of the vanishing of the isospin-symmetric
contribution to this scattering length at leading order in chiral perturbation
theory. We further demonstrate that these corrections can explain the bulk of
the discrepancy between the recent experimental data on pionic hydrogen and
pionic deuterium. We also give the first determination of the electromagnetic
low-energy constant f1.Comment: 4 pages, 1 postscript figure, uses REVTEX styl
Chiral unitary meson-baryon dynamics in the presence of resonances: Elastic pion-nucleon scattering
We develop a novel approach to chiral meson-baryon dynamics incorporating
unitarity constraints and explicit resonance fields. It is based on the most
general structure of any pion-nucleon partial wave amplitude neglecting the
unphysical cuts as derived from the N/D method. This amplitude is then matched
to the one-loop heavy baryon chiral perturbation theory result at third order
and to tree level exchanges of baryon- and meson states in the s,t and u
channels. This generates the left-hand cuts. The unitarization procedure does
not involve form factors or regulator functions. The resonance parameters are
determined from fits to the S- and P-wave pion-nucleon partial wave amplitudes
for energies up to 1.3 GeV. In particular, the is accurately
reproduced whereas scalar and vector meson couplings are less precisely pinned
down. We also obtain a satisfactory description of the N threshold
parameters. Further extensions of this method to coupled channels and the
three-flavor case are briefly discussed.Comment: 23 pp, LaTeX2e, 10 fig
Cusps in K_L --> 3 pi decays
The pion mass difference generates a pronounced cusp in K --> 3 pi decays,
the strength of which is related to the pi pi S-wave scattering lengths. We
apply an effective field theory framework developed earlier to evaluate the
amplitudes for K_L --> 3 pi decays in a systematic manner, where the strictures
imposed by analyticity and unitarity are respected automatically. The
amplitudes for the decay eta --> 3 pi are also given.Comment: 15 pages, 3 figures, uses Elsevier styl
Near threshold ppbar enhancement in the J/psi -> omega ppbar decay
The near-threshold behavior of the ppbar invariant mass spectrum from the
J/psi -> omega ppbar decay reported recently by the BES Collaboration is
analyzed. Contrary to the statement made by the BES Collaboration itself our
study demonstrates that there is indeed a noticeable enhancement in the ppbar
invariant mass spectrum near threshold. Moreover, this enhancement is nicely
reproduced by the final state interaction in the relevant 11S0 ppbar partial
wave as given by the Julich nucleon--antinucleon model. Therefore, and again
contrary to the statement by the BES Collaboration, their new data on J/psi ->
omega ppbar decay in fact strongly support the FSI interpretation of the ppbar
enhancement, seen also in other decay reactions.Comment: 3 pages, 2 figure
Generalized parton correlation functions for a spin-1/2 hadron
The fully unintegrated, off-diagonal quark-quark correlator for a spin-1/2
hadron is parameterized in terms of so-called generalized parton correlation
functions. Such objects, in particular, can be considered as mother
distributions of generalized parton distributions on the one hand and
transverse momentum dependent parton distributions on the other. Therefore, our
study provides new, model-independent insights into the recently proposed
nontrivial relations between generalized and transverse momentum dependent
parton distributions. We find that none of these relations can be promoted to a
model-independent status. As a by-product we obtain the first complete
classification of generalized parton distributions beyond leading twist. The
present paper is a natural extension of our previous corresponding analysis for
spin-0 hadrons.Comment: 41 pages, 3 figures; v2: added referenc
Neutron-proton mass difference in nuclear matter
Isospin-breaking effects in nuclear matter are studied in the framework of a
medium-modified Skyrme model. The proposed effective Lagrangian incorporates
both the medium influence of the surrounding nuclear environment on the single
nucleon properties and an explicit isospin-breaking effect in the mesonic
sector. The approach predicts that the neutron-proton mass difference decreases
in isospin-symmetric nuclear matter but by a very small amount only.Comment: 8 pages, 4 figures, revised versio
A chiral covariant approach to scattering
We analyze vector meson - vector meson scattering in a unitarized chiral
theory based on a chiral covariant framework. We show that a pole assigned to
the the scalar meson can be dynamically generated from the
interaction, while this is not the case for the tensor meson
as found in earlier works. We show that the generation of the
tensor state is untenable due to an artefact of the extreme non-relativistic
kinematics used before. We further consider the effects arising from the
coupling of channels with different orbital angular momenta. We suggest to use
the formalism outlined here to obtain more reliable results for the dynamical
generation of resonances in the vector-vector interaction.Comment: 31 pages, 10 figures, extended version, new section with an improved
solution method, results and conclusions unchange
Scalar mesons in a finite volume
Using effective field theory methods, we discuss the extraction of the mass
and width of the scalar mesons f0(980) and a0(980) from the finite-volume
spectrum in lattice QCD. In particular, it is argued that the nature of these
states can be studied by invoking twisted boundary conditions, as well as
investigating the quark mass dependence of the spectrum.Comment: 18 pages, 3 figure
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