60,189 research outputs found

    Behind the success of the quark model

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    The ground-state three-quark (3Q) potential V3Qg.s.V_{\rm 3Q}^{\rm g.s.} and the excited-state 3Q potential V3Qe.s.V_{\rm 3Q}^{\rm e.s.} are studied using SU(3) lattice QCD at the quenched level. For more than 300 patterns of the 3Q systems, the ground-state potential V3Qg.s.V_{\rm 3Q}^{\rm g.s.} is investigated in detail in lattice QCD with 123×2412^3\times 24 at β=5.7\beta=5.7 and with 163×3216^3\times 32 at β=5.8,6.0\beta=5.8, 6.0. As a result, the ground-state potential V3Qg.s.V_{\rm 3Q}^{\rm g.s.} is found to be well described with Y-ansatz within the 1%-level deviation. From the comparison with the Q-Qˉ\rm\bar Q potential, we find the universality of the string tension as σ3QσQQˉ\sigma_{\rm 3Q}\simeq\sigma_{\rm Q\bar Q} and the one-gluon-exchange result as A3Q12AQQˉA_{\rm 3Q}\simeq\frac12 A_{\rm Q\bar Q}. The excited-state potential V3Qe.s.V_{\rm 3Q}^{\rm e.s.} is also studied in lattice QCD with 163×3216^3\times 32 at β=5.8\beta=5.8 for 24 patterns of the 3Q systems.The energy gap between V3Qg.s.V_{\rm 3Q}^{\rm g.s.} and V3Qe.s.V_{\rm 3Q}^{\rm e.s.}, which physically means the gluonic excitation energy, is found to be about 1GeV in the typical hadronic scale, which is relatively large compared with the excitation energy of the quark origin. This large gluonic excitation energy justifies the great success of the simple quark model.Comment: Talk given at 16th International Conference on Particles and Nuclei (PANIC 02), Osaka, Japan, 30 Sep - 4 Oct 200

    Role of Large Gluonic Excitation Energy for Narrow Width of Penta-Quark Baryons in QCD String Theory

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    We study the narrow decay width of low-lying penta-quark baryons in the QCD string theoryin terms of gluonic excitations. In the QCD string theory, the penta-quark baryon decays via a gluonic-excited state of a baryon and meson system, where a pair of Y-shaped junction and anti-junction is created. Since lattice QCD shows that the lowest gluonic-excitation energy takes a large value of about 1 GeV, the decay of the penta-quark baryon near the threshold is considered as a quantum tunneling process via a highly-excited state (a gluonic-excited state) in the QCD string theory. This mechanism strongly suppresses the decay and leads to an extremely narrow decay width of the penta-quark system.Comment: Talk given at International Conference on the Structure of Baryons (Baryons 04) October 25 - 29, 2004, Ecole Polytechnique, Palaiseau, Franc

    A New Current Regularization of Thirring Model

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    We study an ambiguity of the current regularization in the Thirring model. We find a new current definition which enables to make a comprehensive treatment of the current. Our formulation is simpler than Klaiber's formulation. We compare our result with other formulations and find a very good agreement with their result. We also obtain the Schwinger term and the general formula for any current regularization.Comment: 7 pages, some comments and references added, to appear in Prog. Theor. Phy

    Y-type Flux-Tube Formation in Baryons

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    For more than 300 different patterns of the 3Q systems, the ground-state 3Q potential V3Qg.s.V_{\rm 3Q}^{\rm g.s.} is investigated using SU(3) lattice QCD with 123×2412^3\times 24 at β=5.7\beta=5.7 and 163×3216^3\times 32 at β=5.8,6.0\beta=5.8, 6.0 at the quenched level. As a result of the detailed analyses, we find that the ground-state potential V3Qg.s.V_{\rm 3Q}^{\rm g.s.} is well described with so-called Y-ansatz as V3Q=A3Qi<j1rirj+σ3QLmin+C3QV_{\rm 3Q}=-A_{\rm 3Q}\sum_{i<j}\frac1{|{\bf r}_i-{\bf r}_j|} +\sigma_{\rm 3Q} L_{\rm min}+C_{\rm 3Q}, with the accuracy better than 1%. Here, LminL_{\rm min} denotes the minimal value of total flux-tube length. We also studythe excited-state potential V3Qe.s.V_{\rm 3Q}^{\rm e.s.} using lattice QCD with 163×3216^3\times 32 at β=5.8,6.0\beta=5.8, 6.0 for more than 100 patterns of the 3Q systems. The energy gap between V3Qg.s.V_{\rm 3Q}^{\rm g.s.} and V3Qe.s.V_{\rm 3Q}^{\rm e.s.}, which physically means the gluonic excitation energy, is found to be about 1 GeV in the typical hadronic scale. Finally, we suggest a possible scenario which connects the success of the quark model to QCD.Comment: Talk given at Color Confinement and Hadrons in Quantum Chromodynamics (Confinement 2003), Saitama, Japan, 21-24 July 2003; 5 pages, 4 figure

    Bound States of (Anti-)Scalar-Quarks in SU(3)_c Lattice QCD

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    Light scalar-quarks \phi (colored scalar particles or idealized diquarks) and their color-singlet hadronic states are studied with quenched SU(3)_c lattice QCD in terms of mass generation. We investigate ``scalar-quark mesons'' \phi^\dagger \phi and ``scalar-quark baryons'' \phi\phi\phi as the bound states of scalar-quarks \phi. We also investigate the bound states of scalar-quarks \phi and quarks \psi, i.e., \phi^\dagger \psi, \psi\psi\phi and \phi\phi\psi, which we name ``chimera hadrons''. All the new-type hadrons including \phi are found to have a large mass due to large quantum corrections by gluons, even for zero bare scalar-quark mass m_\phi=0 at a^{-1}\sim 1{\rm GeV}. We conjecture that all colored particles generally acquire a large effective mass due to dressed gluon effects.Comment: Talk given at The 17th International Spin Physics Symposium (SPIN2006), Kyoto, Japan, 2-7 Oct 200

    Universal low-temperature properties of quantum and classical ferromagnetic chains

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    We identify the critical theory controlling the universal, low temperature, macroscopic properties of both quantum and classical ferromagnetic chains. The theory is the quantum mechanics of a single rotor. The mapping leads to an efficient method for computing scaling functions to high accuracy.Comment: 4 pages, 2 tables and 3 Postscript figure

    The Fate of Dark Energy

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    By studying the present cosmological data, particularly on CMB, SNeIA and LSS, we find that the future fate of the universe, for simple linear models of the dark energy equation-of-state, can vary between the extremes of (I) a divergence of the scale factor in as little as 7 Gyr; (II) an infinite lifetime of the universe with dark energy dominant for all future time; (III) a disappearing dark energy where the universe asymptotes as tt \to \infty to a(t)t2/3a(t) \sim t^{2/3} {\it i.e.} matter domination. Our dreadful conclusion is that no amount of data from our past light-cone can select between these future scenarios.Comment: 10 pages LaTeX including 4 eps figures. Minor corrections in tex

    An Improved Search Method for Gravitational Ringing of Black Holes

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    A black hole has characteristic quasi-normal modes that will be excited when it is formed or when the geometry is perturbed. The state of a black hole when the quasi-normal modes are excited is called the gravitational ringing, and detections of it will be a direct confirmation of the existence of black holes. To detect it, a method based on matched filtering needs to be developed. Generically, matched filtering requires a large number of templates, because one has to ensure a proper match of a real gravitational wave with one of template waveforms to keep the detection efficiency as high as possible. On the other hand, the number of templates must be kept as small as possible under limited computational costs. In our previous paper, assuming that the gravitational ringing is dominated by the least-damped (fundamental) mode with the least imaginary part of frequency, we constructed an efficient method for tiling the template space. However, the dependence of the template space metric on the initial phase of a wave was not taken into account. This dependence arises because of an unavoidable mismatch between the parameters of a signal waveform and those given discretely in the template space. In this paper, we properly take this dependence into account and present an improved, efficient search method for gravitational ringing of black holes.Comment: 19 pages, 9 figure

    Candidates for Inflaton in Quiver Gauge Theory

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    The inflaton necessary to implement the mechanism of inflationary cosmology has natural candidates in quiver gauge theory. We discuss the dimensionless coefficients of quartic couplings and enumerate scalars which are singlet under the low-energy gauge group. The inflaton mass is generally predicted to be in the TeV region, close to 4 TeV for one specific unified model. A quartic inflaton potential, and a mutated hybrid inflation, are discussed. They can give adequate inflation and appropriate fluctuations but different spectral indices.Comment: LaTeX 10 page
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