Special Research Centre for the Subatomic Structure of Matter
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The central mission of the Centre is to carry out research activities in the forefront of the fields of theoretical nuclear and particle physics with special emphasis on the strong interactions and their importance in determining the nature of matter.
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Rm. 126, Lvl 1 Physics Building,
University of Adelaide,
SA 5005, Australia
Telephone: +61-8-83133533
Fax: +61-8-83133551
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Item Metadata only Delta electroproduction in a chiral bag model approach(World Scientific Publishing Company, 1997) Lu, D.; Thomas, A.; Williams, A.; Lee, T.S.H.; Roberts, W.We study the \gamma^* N -> \Delta transition amplitudes in a recoil corrected cloudy bag model approach. A modified Peierls-Thouless projection method is used to construct the Galilean invariant baryon states. The pionic contribution is found to be significant. The effect of the recoil correction is to reduce the magnitude of the transition amplitudes at small momentum transfer and to enhance them at modest momentum transfers.Item Open Access Pionic decay of a possible d' dibaryon and the short-range NN interaction(American Physical Society, 1997) Obukhovsky, I. T.; Itonaga, K.; Wagner, Georg; Buchmann, Alfons J.; Faessler, Amand; School of Chemistry and Physics : Physics and Mathematical PhysicsWe study the pionic decay of a possible dibaryon d′→N+N+π in the microscopic quark shell model. The initial d′ dibaryon wave function (JP=0-, T=0) consists of one 1ħω six-quark shell-model s5p[51]X configuration. The most important final six-quark configurations s6[6]X, s4p2[42]X, and (s4p2-s52s)[6]X are properly projected onto the NN channel. The final state NN interaction is investigated by means of two phase-equivalent—but off-shell different—potential models. We demonstrate that the decay width Γd′ depends strongly on the short-range behavior of the NN wave function. In addition, the width Γd′ is very sensitive to the mass and size of the d′ dibaryon. For dibaryon masses slightly above the experimentally suggested value Md′=2.065GeV, we obtain a pionic decay width of Γd′≈0.18–0.32MeV close to the experimental value Γd′≈0.5MeV.Item Metadata only Subtractive renormalization of strong-coupling quenched QED in four dimensions(World Scientific, 1997) Hawes, F.; Sizer, T.; Williams, A.We study renormalized quenched strong-coupling QED in four dimensions in arbitrary covariant gauge, in the Dyson-Schwinger equation formalism. Above the chiral critical coupling, we show that there is no finite chiral limit. This behaviour is found to be independent of the detailed choice of proper vertex, provided that the vertex is consistent with the Ward-Takahashi identity and multiplicative renormalizability. The finite solutions previously reported lie in an unphysical regime of the theory with multiple solutions and oscillating mass functions. This study is consistent with the assertion that strong coupling QED$_4$ does not have a continuum limit in the conventional sense.Item Metadata only Covariant Solutions of the Bethe-Salpeter Equation(World Scientific Publishing Company, 1997) Williams, A.; Kusaka, K.; Simpson, K.Item Open Access Hyperon polarization and single spin left-right asymmetry in inclusive production processes at high energies(American Physical Society, 1997) Liang, Zuo-tang; Boros, Csaba Ladislaus Laszlo; School of Chemistry and Physics : Physics and Mathematical PhysicsIt is shown that the polarization of hyperons observed in high energy collisions using unpolarized hadron beams and unpolarized nucleon or nuclear targets is closely related to the left-right asymmetries observed in single spin inclusive hadron production processes. The relationship is most obvious for the production of the hyperons which have only one common valence quark with the projectile. Examples of this kind are given. Further implications of the existence of large polarization for a hyperon which has two valence quarks in common with the projectile and their consequences are discussed. A comparison with the available data is made. Further tests are suggested.Item Metadata only Variation of hadron masses in finite nuclei(World Scientific Publishing Company, 1997) Saito, K.; Tsushima, K.; Thomas, A.; International Symposium on Non-Nucleonic Degrees of Freedom Detected in Nuclei (1996 : Osaka, Japan)Using a self-consistent, Hartree description for both infinite nuclear matter and finite nuclei based on a relativistic quark model (the quark-meson coupling model), we investigate the variation of the masses of the non-strange vector mesons, the hyperons and the nucleon in infinite nuclear matter and in finite nuclei.Item Metadata only Abelian dominance and adjoint color sources(1997) Poulis, Grigorios I.Item Metadata only To Remarks Concerning the Signs of the Light Quark Masses(1997) Genz, H.Item Metadata only The d/u Ratio and Perturbative QCD(World Scientific Publishing Company, 1997) Thomas, A.; Melnitchouk, W.Item Metadata only Quark degrees of freedom in finite nuclei(World Scientific Publishing Company, 1997) Tsushima, K.; Saito, K.; Thomas, A.Properties of finite nuclei are investigated based on relativistic Hartree equations which have been derived from a relativistic quark model of the structure of bound nucleons. Nucleons are assumed to interact through the (self-consistent) exchange of scalar ($\sigma$) and vector ($\omega$ and $\rho$) mesons at the quark level. The coupling constants and the mass of the $\sigma$-meson are determined from the properties of symmetric nuclear matter and the rms charge radius in $^{40}$Ca. Calculated properties of static, closed-shell nuclei, as well as symmetric nuclear matter are compared with experimental data and with the results of Quantum Hadrodynamics (QHD).Item Open Access Scaling and confinement aspects of tadpole improved SU(2) lattice gauge theory and its Abelian projection(American Physical Society, 1997) Poulis, Grigorios I.; School of Chemistry and Physics : Physics and Mathematical PhysicsUsing a tadpole-improved SU(2) gluodynamics action, the non-Abelian potential and the Abelian potential after the Abelian projection are computed. Rotational invariance is found restored at coarse lattices both in the non-Abelian theory and in the effective Abelian theory resulting from the maximal Abelian projection. Asymptotic scaling is tested for the SU(2) string tension. Deviation of the order of 6% is found for lattice spacings between 0.27 and 0.06 fm. Evidence for asymptotic scaling and scaling of the monopole density in maximal Abelian projection is also seen, but not at coarse lattices. The scaling behavior is compared with analyses of Wilson action results, using bare and renormalized coupling schemes. Using extended monopoles, evidence is found that the gauge dependence of the Abelian projection reflects short distance fluctuations, and may thus disappear at large scales.Item Metadata only CVC in Particle Physics(World Scientific Publishing Company, 1997) Thomas, A.We review the hypothesis of the conserved vector current (CVC) within the Standard Model. In addition to the classic tests, such as pion beta decay and neutrino scattering, we mention recent tests involving LEP data. As well as providing a clear indication that the isovector current is not conserved, rho-omega mixing offers a fascinating opportunity to study CP violation at B-factories and we outline these ideas. Finally we briefly touch on a new approach to mass generation in the Standard Model which, for example, leads to the up-down mass difference which breaks CVC.Item Metadata only Mögliche und unmögliche VergröBerungen(1997) Genz, H.Item Metadata only Self-consistent description of Λ hypernuclei in the quark-meson coupling model(Elsevier B.V., 1997) Tsushima, K.; Saito, K.; Thomas, A.The quark-meson coupling (QMC) model, which has been successfully used to describe the properties of both finite nuclei and infinite nuclear matter, is applied to a study of Λ hypernuclei. With the assumption that the (self-consistent) exchanged scalar, and vector, mesons couple only to the u and d quarks, a very weak spin-orbit force in the Λ-nucleus interaction is achieved automatically. This is a direct consequence of the SU(6) quark model wave function of the Λ used in the QMC model. Possible implications and extensions of the present investigation are also discussed. © 1997 Elsevier Science B.V.Item Metadata only Resonance model study of strangeness production in pp collisions(ELSEVIER SCIENCE BV, 1997) Tsushima, K.; Sibirtsev, A.; Thomas, A.Results for the energy dependence of the elementary kaon production cross sections in proton-proton collisions are reported. Calculations are performed within an extended version of the resonance model which was used for the previous studies of elementary kaon production in pion-nucleon and pion-Δ collisions. Although the model treatment is within the empirical tree level (observed widths for the resonances are used), it is fully relativistic, and includes all relevant baryon resonances up to 2 GeV. One of the purposes of this study is to provide the results for the simulation codes of subthreshold kaon production in heavy ion collisions. This is the first, consistent study of the elementary kaon production reactions including both πB and BB (B = N, Δ) collisions on the same footing. Comparisons are made between the calculated results and the existing semi-empirical parametrizations which are widely used for the simulation codes, as well as the experimental data.Item Metadata only Naturalness in the quark-meson coupling model(ELSEVIER SCIENCE BV, 1997) Saito, K.; Tsushima, K.; Thomas, A.The quark-meson coupling (QMC) model is examined using Georgi's "naive dimensional analysis". We argue that the QMC model is quite natural as an effective field theory for nuclei. © 1997 Elsevier Science B.V.Item Metadata only Quarks in Finite Nuclei(C S I R O PUBLICATIONS, 1997) Guichon, P.; Saito, K.; Thomas, A.We describe the development of a theoretical description of the structure of finite nuclei based on a relativistic quark model of the structure of the bound nucleons which interact through the (self-consistent) exchange of scalar and vector mesons.Item Metadata only Polarized Deep Inelastic Scattering(C S I R O PUBLICATIONS, 1997) Steffens, F.; Thomas, A.; Joint Japan/Australia Workshop (15 Nov 1995 - 24 Nov 1995 : UNIV ADELAIDE, ADELAIDE, AUSTRALIA)We give an overview of present calculations involving the proton spin structure function. It is shown that a significant part of the discepancy between the data and the Ellis-Jaffe sum-rule may arise through the axial anomaly if the gluons within the proton are strongly polarized. While a quark model, such as the MIT bag, does not include the anomaly, and therefore cannot be expected to reproduce the spin structure function, it does give a rather good description of recent data which is anomaly free, such as the distribution of polarized, valence up-quarks in the proton.Item Open Access Variation of hadron masses in finite nuclei(American Physical Society, 1997) Saito, K.; Tsushima, K.; Thomas, A.The quark-meson coupling model, based on a mean-field description of nonoverlapping nucleon bags bound by the self-consistent exchange of σ, ω, and ρ mesons, is extended to investigate the change of hadron properties in finite nuclei. Relativistic Hartree equations for spherical nuclei have been derived from a relativistic quark model of the structure of bound nucleons and mesons. Using this unified, self-consistent description of both infinite nuclear matter and finite nuclei, we investigate the properties of some closed-shell nuclei and study the changes in the hadron masses of the nonstrange vector mesons, the hyperons, and the nucleon in those nuclei. We find a new, simple scaling relation for the changes of the hadron masses, which can be described in terms of the number of nonstrange quarks in the hadron and the value of the scalar mean field in a nucleus.Item Open Access ρ-meson mass in light nuclei(American Physical Society, 1997) Saito, K.; Tsushima, K.; Thomas, A.The quark-meson coupling (QMC) model is applied to a study of the mass of the ρ-meson in helium and carbon nuclei. The average mass of a ρ-meson formed in ³,⁴He and ¹²C is expected to be around 730, 690, and 720 MeV, respectively.