Proper-time methods in the presence of non-constant background fields

A formalism is developed to enable the construction of the effective action and related quantities in QED for the case of time-varying background electric fields. Some examples are studied and evidence is sought for a possible transition to a phase in which chiral symmetry is spontaneously broken. YCTP-P14-94Comment: 13 pages, YCTP-P14-9

Pionic Content of Rho-N-N and Rho-N-Delta Vertex Functions

The dynamical content of rho-N-N and rho-N-Delta vertex functions is studied with a mesonic model. A set of coupled integral equations satisfied by these vertex functions were solved self-consistently. These soulutions indicate that the dominant mesonic content arises from di-pion dynamics. With the experimentally determined pion-baryon-baryon coupling constants and ranges as input, the model predicts a g_{\rho NN} that agrees with the meson-exchange-potential results. On the other hand, it predicts a smaller f_{\rho N\Delta} and much softer form factors. Implications of the findings on the use of phenomenological coupling constants in nuclear reaction studies are discussed.Comment: 9 pages, 2 figures will be furnished upon request; LA-UR-94-126

Changes in the radius of a nucleon in interaction with another nucleon

We consider a two-nucleon system described by two different skyrmion models that provide attraction for the central NN potential. One of these models is based on the product ansatz and the other on dilaton coupling. Within these models we ask the question, To what degree does the nucleon swell or shrink when the internucleon separation distance is appropriate to attraction or repulsion? We find typically swelling of 3 to 4 percent for central attraction of some 40 to 50 MeV.Comment: Nine pages of plain TeX plus two uuencoded figure

Quark and Nucleon Self-Energy in Dense Matter

In a recent work we introduced a nonlocal version of the Nambu--Jona-Lasinio(NJL) model that was designed to generate a quark self-energy in Euclidean space that was similar to that obtained in lattice simulations of QCD. In the present work we carry out related calculations in Minkowski space, so that we can study the effects of the significant vector and axial-vector interactions that appear in extended NJL models and which play an important role in the study of the $\rho$, $\omega$ and $a_1$ mesons. We study the modification of the quark self-energy in the presence of matter and find that our model reproduces the behavior of the quark condensate predicted by the model-independent relation $_{\rho} = <\bar qq>_0(1-\sigma_N\rho_N/f_{\pi}^2m_{\pi}^2 +...)$, where $\sigma_N$ is the pion-nucleon sigma term and $\rho_N$ is the density of nuclear matter. (Since we do not include a model of confinement, our study is restricted to the analysis of quark matter. We provide some discussion of the modification of the above formula for quark matter.) The inclusion of a quark current mass leads to a second-order phase transition for the restoration of chiral symmetry. That restoration is about 80% at twice nuclear matter density for the model considered in this work. We also find that the part of the quark self-energy that is explicitly dependent upon density has a strong negative Lorentz-scalar term and a strong positive Lorentz-vector term, which is analogous to the self-energy found for the nucleon in nuclear matter when one makes use of the Dirac equation for the nucleon. In this work we calculate the nucleon self -energy in nuclear matter using our model of the quark self-energy and obtain satisfactory results.Comment: 19 pages, 8 figures, 2 tables, revte

Assessment of Junior Doctor performance: a validation study

BACKGROUND: In recent years, Australia has developed a National Junior Doctor Curriculum Framework that sets out the expected standards and describes areas of performance for junior doctors and through this has allowed a national approach to junior doctor assessment to develop. Given the significance of the judgments made, in terms of patient safety, development of junior doctors, and preventing progression of junior doctors moving to the next stage of training, it is essential to develop and validate assessment tools as rigorously as possible. This paper reports on a validation study of the Junior Doctor Assessment Tool as used for PGY1 doctors to evaluate the psychometric properties of the instrument and to explore the effect of length of experience as a PGY1 on assessment scores. METHODS: This validation study of the Australian developed Junior Doctor Assessment Tool as it was used in three public and other associated hospitals in Western Australia for PGY1 across a two year period addressed two core aims, namely: (1) to evaluate the psychometric properties of the instrument; (2) to explore the effect of length of experience as a PGY1 on assessment scores. RESULTS: The highest mean scores were for professional behaviours, teamwork and interpersonal skills and the lowest were for procedures. Most junior doctors were assessed three or more times and scores were not different in the first rotation compared to subsequent rotations. While statistically significant, there appeared to be little practical influence on scores obtained by the number of times they were assessed. Principal component analysis identified two principal components of junior doctor performance are being assessed rather than the commonly reported three. A Cronbach Alpha of .883 was calculated for the 10 item scale. CONCLUSIONS: Now that the components of the tool have been analysed it will be more meaningful and potentially more influential to consider these factors on the potential educational impact of this assessment process for monitoring junior doctor development and progression

Quark-Antiquark Bound States within a Dyson-Schwinger Bethe-Salpeter Formalism

Pion and kaon observables are calculated using a Dyson-Schwinger Bethe-Salpeter formalism. It is shown that an infrared finite gluon propagator can lead to quark confinement via generation of complex mass poles in quark propagators. Observables, including electromagnetic form factors, are calculated entirely in Euclidean metric for spacelike values of bound state momentum and final results are extrapolated to the physical region.Comment: Minor typographical corrections. Accepted for publication in Nucl. Phys.

Squeezed gluon vacuum and the global colour model of QCD

We discuss how the vacuum model of Celenza and Shakin with a squeezed gluon condensate can explain the existence of an infrared singular gluon propagator frequently used in calculations within the global colour model. In particular, it reproduces a recently proposed QCD-motivated model where low energy chiral parameters were computed as a function of a dynamically generated gluon mass. We show how the strength of the confining interaction of this gluon propagator and the value of the physical gluon condensate may be connected.Comment: 13 pages, LaTe

Dimensional Reduction and Dynamical Chiral Symmetry Breaking by a Magnetic Field in 3+13+1 Dimensions

It is shown that in $3+1$ dimensions, a constant magnetic field is a catalyst of dynamical chiral symmetry breaking, leading to generating a fermion mass even at the weakest attractive interaction between fermions. The essence of this effect is the dimensional reduction $D \rightarrow D-2$ ($3+1 \rightarrow 1+1$) in the dynamics of fermion pairing in a magnetic field. The effect is illustrated in the Nambu-Jona-Lasinio model. Possible applications of this effect are briefly discussed.Comment: 13 pages, LaTeX, no figure

Quark Propagation in the Quark-Gluon Plasma

It has recently been suggested that the quark-gluon plasma formed in heavy-ion collisions behaves as a nearly ideal fluid. That behavior may be understood if the quark and antiquark mean-free- paths are very small in the system, leading to a "sticky molasses" description of the plasma, as advocated by the Stony Brook group. This behavior may be traced to the fact that there are relatively low-energy $q\bar{q}$ resonance states in the plasma leading to very large scattering lengths for the quarks. These resonances have been found in lattice simulation of QCD using the maximum entropy method (MEM). We have used a chiral quark model, which provides a simple representation of effects due to instanton dynamics, to study the resonances obtained using the MEM scheme. In the present work we use our model to study the optical potential of a quark in the quark-gluon plasma and calculate the quark mean-free-path. Our results represent a specific example of the dynamics of the plasma as described by the Stony Brook group.Comment: 17 pages, 4 figures, revtex

Landau-gauge condensates from the quark propagator on the lattice

We compute the dimension-2 condensate, , and the dimension-4 mixed condensate, , from the recent quenched lattice results for the quark propagator in the Landau gauge. We fit the lattice data to the Operator Product Expansion in the "fiducial" region 1.2 GeV < Q < 3 GeV. Our result for the dynamical gluon mass at the scale of 10 GeV^2 is m_A=600-650 MeV, in agreement with independent determinations. For the mixed Landau gauge condensate of dimension-4 we get alpha_s = (-0.11 +/- 0.03) GeV^4. This value is an order of magnitude larger than the gluon condensate.Comment: 4 pages, 3 figures, references adde