209 research outputs found
Nucleon magnetic moments in an extended chiral constituent quark model
We present results for the nucleon magnetic moments in the context of an
extended chiral constituent quark model based on the mechanism of the Goldstone
boson exchange, as suggested by the spontaneous breaking of chiral symmetry in
QCD. The electromagnetic charge-current operator is consistently deduced from
the model Hamiltonian, which includes all force components for the
pseudoscalar, vector and scalar meson exchanges. Thus, the continuity equation
is satisfied for each piece of the interaction, avoiding the introduction of
any further parameter. A good agreement with experimental values is found. The
role of isoscalar two-body operators, not constrained by the continuity
equation, is also investigated.Comment: 7 pages, 1 table, submitted for publication to Phys. Lett. B,
elsart.sty/elsart12.sty include
Calculation of fragmentation functions in two-hadron semi-inclusive processes
We investigate the properties of interference fragmentation functions arising
from the emission of two leading hadrons inside the same jet for inclusive
lepton-nucleon deep-inelastic scattering. Using an extended spectator model for
the mechanism of the hadronization, we give a complete calculation and
numerical estimates for the examples of a proton-pion pair produced with
invariant mass on the Roper resonance, and of two pions produced with invariant
mass close to the mass. We discuss azimuthal angular dependence of the
leading order cross section to point up favourable conditions for extracting
transversity from experimental data.Comment: 5 pages, 3 figures in .eps format, AIP and epsfig styles included, to
appear in proceedings of "Second Workshop on Physics with an Electron
Polarized Light Ion Collider", MIT, Sept. 14-16, 200
Nuclear transparency in quasielastic A(e,e'p): intranuclear cascade versus eikonal approximation
The problem of nuclear propagation through the nuclear medium in quasielastic
A(e,e'p) reactions is discussed in the kinematic range 1<Q^2<7 (GeV/c)^2. The
coefficient of nuclear transparency is calculated for each Q^2 in the framework
of the intranuclear cascade model (INC) and of the eikonal approximation (EA).
The predictions of both models are in good agreement with each other and with
experimental data recently obtained at SLAC, BATES and TJNAF. The EA gives an
explanation of the Q^2 behaviour of the transparency coefficient as a kinematic
effect related to the superposition of contributions from each target shell.Comment: RevTeX, 23 pages, 11 figures separately, submitted to Phys. Rev.
High-momentum proton removal from 16O and the (e,e'p) cross section
The cross section for the removal of high-momentum protons from 16O is
calculated for high missing energies. The admixture of high-momentum nucleons
in the 16O ground state is obtained by calculating the single-hole spectral
function directly in the finite nucleus with the inclusion of short-range and
tensor correlations induced by a realistic meson-exchange interaction. The
presence of high-momentum nucleons in the transition to final states in 15N at
60-100 MeV missing energy is converted to the coincidence cross section for the
(e,e'p) reaction by including the coupling to the electromagnetic probe and the
final state interactions of the outgoing proton in the same way as in the
standard analysis of the experimental data. Detectable cross sections for the
removal of a single proton at these high missing energies are obtained which
are considerably larger at higher missing momentum than the corresponding cross
sections for the p-wave quasihole transitions. Cross sections for these
quasihole transitions are compared with the most recent experimental data
available.Comment: 26 RevTex pages, 7 ps figure
The five gradients inequality on differentiable manifolds
The goal of this paper is to derive the so-called five gradients inequality
for optimal transport theory for general cost functions on two class of
differentiable manifolds: locally compact Lie groups and compact Riemannian
manifolds with Ricci curvature bounded from below.Comment: 29 page
Transverse-momentum distributions in a diquark spectator model
All the leading-twist parton distribution functions are calculated in a
spectator model of the nucleon, using scalar and axial-vector diquarks. Single
gluon rescattering is used to generate T-odd distribution functions. Different
choices for the diquark polarization states are considered, as well as a few
options for the form factor at the nucleon-quark-diquark vertex. The results
are listed in analytic form and interpreted in terms of light-cone wave
functions. The model parameters are fixed by reproducing the phenomenological
parametrization of unpolarized and helicity parton distributions at the lowest
available scale. Predictions for the other parton densities are given and,
whenever possible, compared with available phenomenological parametrizations.Comment: 42 pages, 13 figures in .eps format. RevTeX style. Minor typos
corrected, added one referenc
Electroweak properties of baryons in a covariant chiral quark model
The proton and neutron electromagnetic form factors and the nucleon axial
form factor have been calculated in the Goldstone-boson exchange
constituent-quark model within the point-form approach to relativistic quantum
mechanics. The results, obtained without any adjustable parameter nor quark
form factors, are, due to the dramatic effects of the boost required by the
covariant treatment, in striking agreement with the data.Comment: Proceedings of the Conference N*2001, Mainz; 4 pages, 3 figures
included in eps format; World Scientific style file include
Covariant axial form factor of the nucleon in a chiral constituent quark model
The axial form factor G_A of the nucleon is investigated for the
Goldstone-boson-exchange constituent quark model using the point-form approach
to relativistic quantum mechanics. The results, being covariant, show large
contributions from relativistic boost effects. The predictions are obtained
directly from the quark-model wave functions, without any further input such as
vertex or constituent-quark form factors, and fall remarkably close to the
available experimental data.Comment: 10 pages, 1 figure in .eps format, typeset with Elsevier elsart style
files included. Revised version with a newly added section about discussion
of results. To appear in Phys. Lett.
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