Special Research Centre for the Subatomic Structure of Matter
Permanent URI for this community
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.
News
CSSM,
Rm. 126, Lvl 1 Physics Building,
University of Adelaide,
SA 5005, Australia
Telephone: +61-8-83133533
Fax: +61-8-83133551
Browse
Browsing Special Research Centre for the Subatomic Structure of Matter by Title
Now showing 1 - 20 of 501
Results Per Page
Sort Options
Item Open Access 1/mQ corrections to the Bethe-Salpeter equation for ΛQ in the diquark picture(American Physical Soc, 2000) Guo, X.; Thomas, A.; Williams, A.Corrections of order 1/m_Q (Q=b or c) to the Bethe-Salpeter (B-S) equation for \Lambda_Q are analyzed on the assumption that the heavy baryon \Lambda_Q is composed of a heavy quark and a scalar, light diquark. It is found that in addition to the one B-S scalar function in the limit m_Q -> \infty, two more scalar functions are needed at the order 1/m_Q. These can be related to the B-S scalar function in the leading order. The six form factors for the weak transition \Lambda_b -> \Lambda_c are expressed in terms of these wave functions and the results are consistent with heavy quark effective theory to order 1/m_Q. Assuming the kernel for the B-S equation in the limit m_Q -> \infty to consist of a scalar confinement term and a one-gluon-exchange term we obtain numerical solutions for the B-S wave functions, and hence for the $\Lambda_b \to \Lambda_c$ form factors to order 1/m_Q. Predictions are given for the differential and total decay widths for \Lambda_b -> \Lambda_c l \bar{\nu}, and also for the nonleptonic decay widths for \Lambda_b -> \Lambda_c plus a pseudoscalar or vector meson, with QCD corrections being also included.Item Open Access 1⁻⁺ exotic meson at light quark masses(American Physical Soc, 2005) Hedditch, J.; Kamleh, W.; Lasscock, B.; Leinweber, D.; Williams, A.The mass of the 1⁻⁺ exotic meson, created with hybrid interpolating fields, is explored in numerical simulations of quenched QCD on large (20³×40) lattices to obtain good control of statistical and finite volume errors. Using the Fat-Link Irrelevant Clover (FLIC) fermion action, the properties of the 1⁻⁺ are investigated at light quark masses approaching 25 MeV (mπ/mρ≃1/3). Under the standard assumption that the coupling to the quenched a1η′ channel comes with a negative metric, our results indicate that the 1-+ exotic exhibits significant curvature close to the chiral limit, suggesting previous linear extrapolations have overestimated the mass of the 1⁻⁺. We find for the first time in lattice studies a 1⁻⁺ mass consistent with the π1(1600) candidate. We also find a strangeness ±1 JP=1- state with a mass close to 2 GeV.Item Metadata only A clue to the mechanism of LK + production in pp-reactions 1(ELSEVIER SCIENCE BV, 1998) Sibirtsev, A.; Tsushima, K.; Thomas, A.We analyse the pp → pΛK+ total cross section data which were recently measured by the COSY-11 collaboration at an energy 2 MeV above the reaction threshold. Our analysis suggests that the measurement of the invariant mass spectrum for the ΛK+ at energies around 100 MeV above the threshold can provide a new constraint on the theoretical calculations for this reaction. In particular, the measurement can give a clue as to whether the reaction is dominated by resonance excitation or not. Thus, it should contribute to further understanding of the strangeness production mechanism. We show the invariant mass spectra for the ΛK+ system in these optimal kinematic conditions calculated by several approaches, and demonstrate that our suggestion is experimentally feasible. © 1998 Elsevier Science B.V.Item Metadata only A method to unambiguously determine the parity of the Θ⁺ pentaquark(Progress Theoretical Physics Publication Office, 2004) Thomas, A.; Hicks, K.; Hosaka, A.With the recent discovery of the θ(1540) pentaquark, the question of its parity is paramount since this will constrain the correct description of its internal structure. We show that the measurement of the spin singlet and triplet cross sections for the reaction p→p→ → σ+θ+ will unambiguously determine the parity of the θ+.Item Metadata only A new analysis of charge symmetry violation in parton distributions(ELSEVIER SCIENCE BV, 1999) Boros, C.; Steffens, F.; Londergan, J.; Thomas, A.To date, the strongest indication of charge symmetry violation in parton distributions has been obtained by comparing the F2 structure functions from CCFR neutrino data and NMC muon data. We show that in order to make precise tests of charge symmetry with the neutrino data, two conditions must be satisfied. First, the nuclear shadowing calculations must be made explicitly for neutrinos, not simply taken from muon data on nuclei. Second, the contribution of strange and charm quarks should be calculated explicitly using next-to-leading order (NLO) QCD, and the "slow rescaling" charm threshold correction should not be applied to the neutrino data. When these criteria are satisfied, the comparison is consistent with charge symmetry within the experimental errors and the present uncertainty in the strange quark distribution of the nucleon. © 1999 Published by Elsevier Science B.V. All rights reserved.Item Metadata only A new slant on hadron structure(Indian Academy Sciences, 2001) Detmold, W.; Leinweber, D.; Melnitchouk, W.; Thomas, A.; Wright, S.Rather than regarding the restriction of current lattice QCD simulations to quark masses that are 5–10 times larger than those observed as a problem, we note that this presents a wonderful opportunity to deepen our understanding of QCD. Just as it has been possible to learn a great deal about QCD by treating N c as a variable, so the study of hadron properties as a function of quark mass is leading us to a deeper appreciation of hadron structure. As examples we cite progress in using the chiral properties of QCD to connect hadron masses, magnetic moments, charge radii and structure functions calculated at large quark masses within lattice QCD with the values observed physically.Item Metadata only A Rigorous Ellis-Jaffe Sum Rule(World Scientific, 1998) Thomas, A.; Bass, S.; Crewther, R.; Steffens, F.Item Metadata only A study of the πB → Y K reactions for Kaon production in heavy ion collisions(CSIRO, 1997) Tsushima, K.; Huang, S.; Faessler, A.Parametrizations of total cross sections sucient for all channels of the πB → Y K reactions are completed using a resonance model. As well as discussing the πN → ΛK reactions, which were not presented in our previous publications, we present the differential cross section for πN → ΛK. This report also aims at presenting supplementary discussions to our previous work.Item Metadata only A theory of the fundamental plasma emission of type-III solar radio bursts(Springer-Verlag, 2002) Alves, M.; Chian, A.; De Moraes, M.; Abalde, J.; Rizzato, F.Results from plasma wave experiments in spacecraft give support to nonlinear interactions involving Langmuir waves, electromagnetic waves and ion-acoustic waves in association with type III solar radio bursts. In this paper we present a theory of the fundamental plasma emission of type-III solar radio bursts. Starting from the generalized Zakharov equations, considering the pump wave as a pair of oppositely propagating Langmuir waves with different amplitudes, and the excitation of electromagnetic and induced Langmuir waves, we obtain a general dispersion relation for the coupled waves. We numerically solve the general dispersion relation using the pump wave amplitude and plasma parameters as observed in the interplanetary medium. We compare our results with previous models. We find that the stability properties depend on the pump wave numbers and on the ratio of wave amplitude between the forward and backward pump wave. The inclusion of a second pump wave allows the simultaneous generation of up and down converted electromagnetic waves. The presence of a second pump with different amplitude from the first one brings a region of convective instability not present when amplitudes are the same.Item Open Access A toy model of (grand) unified monopoles(Scuola Internazionale Superiore di Studi Avanzati, 2005) Von Smekal, L.; Tok, T.; de Forcrand, P.; International Symposium on Lattice Field Theory (23rd : 2005 : Dublin, Ireland); Irving, A.; McNeile, C.; Michael, C.We explore the old idea that, in a theory containing several gauge groups, the topological defects of one gauge group coincide with those of another gauge group. This simple ’unification’ constraint has deep consequences, the best known of which is a natural explanation of the fractional electric charge of quarks. Here we explore the consequences of this idea for the phase diagram, in a toy model U(1)xU(1).Item Metadata only Item Metadata only Abelian dominance and adjoint color sources(1997) Poulis, Grigorios I.Item Open Access Accelerated overlap fermions(American Physical Soc, 2002) Kamleh, W.; Adams, D.; Leinweber, D.; Williams, A.; Special Research Centre for the Subatomic Structure of MatterNumerical evaluation of the overlap Dirac operator is difficult since it contains the sign function ε(Hw) of the Hermitian Wilson-Dirac operator Hw with a negative mass term. The problems are due to Hw having very small eigenvalues on the equilibrium background configurations generated in current day Monte Carlo simulations. Since these are a consequence of the lattice discretization and do not occur in the continuum version of the operator, we investigate in this paper to what extent the numerical evaluation of the overlap can be accelerated by making the Wilson-Dirac operator more continuum-like. Specifically, we study the effect of including the clover term in the Wilson-Dirac operator and smearing the link variables in the irrelevant terms. In doing so, we have obtained a factor of 2 speedup by moving from the Wilson action to a fat link irrelevant clover action as the overlap kernel.Item Metadata only Alfvén boundary crisis(World Scientific Publ Co Pte Ltd, 2002) Chian, A.; Borotto, F.; Rempel, E.A new transition mechanism to Alfvén chaos via boundary crisis is reported. This crisis appears in a complex plasma region in the presence of a large number of coexisting attractors. We characterize an example of double boundary crises using the unstable periodic orbit determined from the numerical solution of the driven-dissipative derivative nonlinear Schrödinger equation, and demonstrate how the same unstable periodic orbit causes the appearance/disappearance of two chaotic attractors due to two successive homoclinic tangencies.Item Metadata only An algorithm for obtaining reliable priors for constrained-curve fits(Elsevier Science BV, 2004) Draper, Terrence; Dong, Shao-Jing; Horvath, Ivan; Lee, Frank X.; Mathur, Nilmani; Zhang, Jian-BoItem Metadata only An Abraham-Lorentz-like equation for the electron from the worldline variational approach to QED(Springer, 2004) Rosenfelder, R.; Schreiber, A.The variational equation for the mean square displacement of the electron in the polaron worldline approach to quenched QED can be cast into a form which closely resembles the classical Abraham-Lorentz equation but without the conceptual and practical diseases of the latter. The connection with delay equations describing field retardation effects is also established. As applications we solve this integro-differential equation numerically for various values of the coupling constant and cut-off and re-derive the variational approximation to the anomalous mass dimension of the electron found recently.Item Metadata only Analysis of the Λp final-state interaction in the reaction p+p→K+(Λp)(Springer, 2004) Hinterberger, F.; Sibirtsev, A.Item Metadata only Application of r-w Mixing in CP Violating B-Decays(1998) Thomas, A.Item Metadata only Are the contemporary financial fluctuations sooner converging to normal?(Acta Physica Polonica B, 2003) Drozdz, S.; Kwapien, Jaroslaw; Grummer, F.; Ruf, F.; Speth, J.Item Metadata only Are η- and ω-nuclear states bound?(Elsevier, 1998) Tsushima, K.; Lu, D.; Thomas, A.; Saito, K.We investigate theoretically whether it is feasible to detect η- and ω-nucleus bound states. As well as the closed shell nuclei, 16O, 40Ca, 90Zr and 208Pb, we also investigate 6He, 11B and 26Mg, which are the final nuclei in the proposed experiment involving the (d,3He) reaction at GSI. Potentials for the η and ω mesons in these nuclei are calculated in local density approximation, embedding the mesons in the nucleus described by solving the mean-field equations of motion in the QMC model. Our results suggest that one should expect to find η- and ω-nucleus bound states in all these nuclei. © 1998 Elsevier Science B.V. All rights reserved.