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Search Results: 1 - 10 of 715881 matches for " M. A. Green "
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Many-body CPA for the Holstein-DE model
A. C. M. Green
Physics , 2000, DOI: 10.1103/PhysRevB.63.205110
Abstract: A many-body coherent potential approximation (CPA) previously developed for the double exchange (DE) model is extended to include coupling to local quantum phonons. The Holstein-DE model studied (equal to the Holstein model for zero Hund coupling) is considered to be a simple model for the colossal magnetoresistance manganites. We concentrate on effects due to the quantisation of the phonons, such as the formation of polaron subbands. The electronic spectrum and resistivity are investigated for a range of temperature and electron-phonon coupling strengths. Good agreement with experiment is found for the Curie temperature and resistivity with intermediate electron-phonon coupling strength, but phonon quantisation is found not to have a significant effect in this coupling regime.
Bridges from Lattice QCD to Nuclear Physics
A. M. Green
Physics , 2004,
Abstract: A review is given of attempts to bridge the gap between everyday particle and nuclear physics - involving many quarks - and the basic underlying theory of QCD that can only be evaluated exactly for few quark systems. Even the latter requires the original theory of QCD to be discretised to give Lattice QCD - but this modification can still yield exact results for the original theory. These LQCD results can then be considered on a similar footing to experimental data - namely as cornerstones that must be fitted by phenomenological models. In this way, the hope is that "QCD inspired" models can become more and more "QCD based" models, by fixing - in the few-quark case where LQCD can be carried out - the form of these models in such a way that they can be extended to multi-quark systems.
Variational calculations for K-few-nucleon systems
Wycech, S.;Green, A. M.
High Energy Physics - Phenomenology , 2008, DOI: 10.1103/PhysRevC.79.014001
Abstract: Deeply bound KNN, KNNN and KNNNN states are discussed. The effective force exerted by the K meson on the nucleons is calculated with static nucleons. Next the binding energies are obtained by solving the Schrodinger equation or by variational calculations. The dominant attraction comes from the S-wave Lambda(1405) and an additional contribution is due to Sigma(1385). The latter state is formed at the nuclear peripheries and absorbs a sizable piece of the binding energy. It also generates new branches of quasi-bound states. The lowest binding energies based on a phenomenological KN input fall into the 40-80 MeV range for KNN, 90-150 MeV for KNNN and 120-220 MeV for K-alpha systems. The uncertainties are due to unknown KN interactions in the distant subthreshold energy region.
An interquark potential model for multi-quark systems
A. M. Green,P. Pennanen
Physics , 1998, DOI: 10.1103/PhysRevC.57.3384
Abstract: A potential model for four interacting quarks is constructed in SU(2) from six basis states -- the three partitions into quark pairs, where the gluon field is either in its ground state or first excited state. With four independent parameters to describe the interactions connecting these basis states, it is possible to fit 100 pieces of data -- the ground and first excited states of configurations from six different four-quark geometries calculated on a 16^3*32 lattice.
A model for multi-quark systems
A. M. Green,P. Pennanen
Physics , 1997, DOI: 10.1016/S0370-2693(98)00300-1
Abstract: As a step towards understanding multi-quark systems abundant in nature we construct a model that reproduces the binding energies of static four-quark systems. These energies have been calculated using SU(2) lattice gauge theory for a set of six different geometries representative of the general case. The model is based on ground and excited state two-body potentials and multi-quark interaction terms.
On eta-pi mixing close to the eta-Helium threshold
A. M. Green,S. Wycech
Physics , 2003, DOI: 10.1103/PhysRevC.68.061601
Abstract: A K-matrix formalism is used to relate the amplitudes for the three reactions pd --> 3He eta, pi- 3H --> 3He eta and pd --> 3H pi+. Free parameters are fitted to the available experimental data and an extrapolation below the eta 3He threshold is made to see the origin of the eta 3He threshold enhancement. The existence of a virtual -- and not a quasi-bound -- state finds support in the data. The K-matrix permits a discussion of eta-pi mixing. A mixing parameter of 0.010(5), i.e. a mixing angle theta =0.6(3) degrees, is extracted from a best fit to the very recent pd --> 3He pi0 reaction data.
The Production of the Exotic Atoms $π^+π^-$, $K^+π^-$ and $K^+K^-$
S. Wycech,A. M. Green
Physics , 1993, DOI: 10.1016/0375-9474(93)90207-E
Abstract: Estimates are made of the signals to be expected in the production of the exotic atoms Pionium ($\pi^+\pi^-$), Kaonium ($K^+K^-$) and also $K^+\pi^-$ in pp, pd and $e^+e^-$ reactions. Such experiments are now being undertaken or contemplated at CELSIUS, COSY, Indiana and SATURNE.
The Eta-Nucleon Scattering Length and Effective Range
A. M. Green,S. Wycech
Physics , 1997, DOI: 10.1103/PhysRevC.55.R2167
Abstract: The coupled eta N, pi N system is described by a K-matrix method. The parameters in this model are adjusted to get an optimal fit to pi N -> pi N, pi N -> eta N and gamma N -> eta N data in an energy range of about 100MeV each side of the eta threshold. In the notation T^(-1)+iq_(eta) = 1/a + (r_0)/2 q^2_(eta) + s q^4_(eta), q_(eta) being the momentum in the eta N center-of-mass, the resulting effective range parameters for eta N scattering are found to be a(fm) = 0.75(4)-i0.27(3), r_0(fm) = -1.50(13)-i0.24(4) and s(fm^3) = -0.10(2)-i0.01(1)
Two Quark Potentials
G. Bali,A. M. Green
Physics , 2004,
Abstract: In this Chapter QCD interactions between a quark and an anti-quark are discussed. In the heavy quark limit these potentials can be related to quarkonia and $1/m$ corrections can be systematically determined. Excitations of the ground state potential provide an entry point into the phenomenology of quark-gluon hybrids. The short-distance behaviour of non-perturbative potentials can serve as a test of resummation and convergence of perturbative expansions. Torelons and potentials between non-fundamental colour charges offer a window into the origin of the confinement mechanism and relate to effective string descriptions of low energy aspects of QCD.
Variational calculations for K-few-nucleon systems
S. Wycech,A. M. Green
Physics , 2008, DOI: 10.1103/PhysRevC.79.014001
Abstract: Deeply bound KNN, KNNN and KNNNN states are discussed. The effective force exerted by the K meson on the nucleons is calculated with static nucleons. Next the binding energies are obtained by solving the Schrodinger equation or by variational calculations. The dominant attraction comes from the S-wave Lambda(1405) and an additional contribution is due to Sigma(1385). The latter state is formed at the nuclear peripheries and absorbs a sizable piece of the binding energy. It also generates new branches of quasi-bound states. The lowest binding energies based on a phenomenological KN input fall into the 40-80 MeV range for KNN, 90-150 MeV for KNNN and 120-220 MeV for K-alpha systems. The uncertainties are due to unknown KN interactions in the distant subthreshold energy region.
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