26 research outputs found
QCD sum rules and chiral logarithms
Standard QCD sum-rule analyses of the nucleon mass give results that are
inconsistent with chiral perturbation theory due to an overly simple continuum
ansatz on the phenomenological side of the sum rule. We show that a careful
treatment of the continuum, including - states and other states with
virtual pions, resolves the inconsistency associated with chiral logs.Comment: 10 pages, no figure
Variations of Hadron Masses and Matter Properties in Dense Nuclear Matter
Using a self-consistent quark model for nuclear matter we investigate
variations of the masses of the non-strange vector mesons, the hyperons and the
nucleon in dense nuclear matter (up to four times the normal nuclear density).
We find that the changes in the hadron masses can be described in terms of the
value of the scalar mean-field in matter. The model is then used to calculate
the density dependence of the quark condensate in-medium, which turns out to be
well approximated by a linear function of the nuclear density. Some relations
among the hadron properties and the in-medium quark condensate are discussed.Comment: 22 pages, University of Adelaide preperint ADP-94-20/T160, submitted
to Physical Review
Role of heavy-meson exchange in pion production near threshold
Recent calculations of -wave pion production have severely underestimated
the accurately known \ total cross section near
threshold. In these calculations, only the single-nucleon axial-charge operator
is considered. We have calculated, in addition to the one-body term, the
two-body contributions to this reaction that arise from the exchange of mesons.
We find that the inclusion of the scalar -meson exchange current (and
lesser contributions from other mesons) increases the cross section by about a
factor of five, and leads to excellent agreement with the data. The results are
neither very sensitive to changes in the distorting potential that generates
the wave function, nor to different choices for the meson-nucleon form
factors. We argue that \ data provide direct
experimental evidence for meson-exchange contributions to the axial current.Comment: 28 Pages, IU-NTC #93-0
What does a change in the quark condensate say about restoration of chiral symmetry in matter?
The contribution of nucleons to the quark condensate in nuclear matter
includes a piece of first order in , arising from the contribution of
low-momentum virtual pions to the sigma commutator. Chiral symmetry
requires that no term of this order appears in the interaction. The mass
of a nucleon in matter thus cannot depend in any simple way on the quark
condensate alone. More generally, pieces of the quark condensate that arise
from low-momentum pions should not be associated with partial restoration of
chiral symmetry.Comment: 9 pages (RevTeX). Definition of effective mass changed; numerical
value of leading nonanalytic term corrected, along with various misprint
QCD phase transitions from relativistic hadron models
The models of translationally invariant infinite nuclear matter in the
relativistic mean field models are very interesting and simple, since the
nucleon can connect only to a constant vector and scalar meson field. Can one
connect these to the complicated phase transitions of QCD ? For an affirmative
answer to this question, one must consider models where the coupling constants
to the scalar and vector fields must depend on density in a non-linear way,
since as such the models are not explicitly chirally invariant. Once this is
ensured, indeed one can derive a quark condensate indirectly from the energy
density of nuclear matter which goes to zero at large density and temperature.
The change to zero condensate indicates a smooth phase transition.Comment: 12 pages latex file, 1 table, 12 Postscript figures. To appear in
Zeit. f. Phys.
QCD Sum Rules for the Isospin-Breaking Axial Correlator with Correct Chiral Behavior
We revisit the QCD sum-rule treatment of the isospin-breaking axial
correlator in light of the recent claim that a previous treatment produced
results incompatible with known chiral constraints. The source of the error in
the previous analysis is identified, and a corrected version of the sum-rule
treatment obtained. It is then shown that, using input from chiral perturbation
theory, one may use the resulting sum rule to extract information on the
leading chiral behavior of isospin-breaking parameters associated with the
coupling of excited pseudoscalar resonances to the axial currents. A rather
accurate extraction is possible for the case of the eta'. Demanding stability
of the sum-rule analysis also allows us to improve the upper bound on the
fourth-order low-energy constant, L_7.Comment: 20 pages (RevTeX), 1 figure (epsf
The pectoralis minor length test: a study of the intra-rater reliability and diagnostic accuracy in subjects with and without shoulder symptoms
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly citedBackground. Postural abnormality and muscle imbalance are thought to contribute to pain and a loss of normal function in the upper body. A shortened pectoralis minor muscle is commonly identified as part of this imbalance. Clinical tests have been recommended to test for shortening of this muscle. The aim of this study was to evaluate the intra-rater reliability and diagnostic accuracy of the pectoralis minor length test. Methods. Measurements were made in 45 subjects with and 45 subjects without shoulder symptoms. Measurements were made with the subjects lying in supine. In this position the linear distance from the treatment table to the posterior aspect of the acromion was measured on two occasions (separated by a minimum of 30 minutes and additional data collection on other subjects to reduce bias) by one rater. The reliability of the measurements was analyzed using intraclass correlation coefficients (ICC), 95% confidence intervals (CI) and standard error of measurement (SEM). The diagnostic accuracy of the test was investigated by determining the sensitivity, specificity, positive and negative likelihood ratios of the test against a 'gold standard' reference. The assessor remained 'blinded' to data input and the measurements were staggered to reduce examiner bias. Results. The pectoralis minor length test was found to have excellent intra-rater reliability for dominant and non-dominant side of the subjects without symptoms, and for the painfree and painful side of the subjects with symptoms. The values calculated for the sensitivity, specificity, positive and negative likelihood ratios suggest this test performed in the manner investigated in this study and recommended in the literature, lacks diagnostic accuracy. Conclusion. The findings of this study suggest that although the pectoralis minor length test demonstrates acceptable clinical reliability, its lack of specificity suggests that clinicians using this test to inform the clinical reasoning process with regard treatment planning must do so with caution. Trial registration. National Research Register: N0060148286.Peer reviewe
Effective Vector Meson Masses in a Cutoff Field Theory
Based on quantum hadrodynamics with a finite cutoff, the effective masses of
vector mesons(\omega, \rho) in nuclear medium are calculated. We use a
low-energy effective Lagrangian which is obtained by integrating high-energy
quantum fluctuations. Although we use an artificial cutoff, the
cutoff-dependence can be removed order by order. It is shown that there is a
strong correlation between the effective \omega -meson mass and the effective
nucleon mass at the normal density. It is also found that the effective
\rho-meson mass m_\rho^* decreases as density increases. The rate of the
decrease becomes smaller at high density. As a result, at the normal density,
the m^*_\rho/m_\rho is 0.85 \sim 0.95.Comment: 15 pages, LateX, 7 eps figures. Email: [email protected]