2,055 research outputs found

    How light can the Higgs be?

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    It is widely believed that, for a given Top mass, the Higgs mass has a lower bound: if m_Higgs is too small, the Higgs vacuum is unstable due to Top dynamics. From vacuum instability, the state-of-the-art calculation of the lower bound is close to the current experimental limit. Using non-perturbative simulations and large N calculations, we show that the vacuum is in fact never unstable. Instead, we investigate the existence of a new lower bound, based on the intrinsic cut-off of this trivial theory.Comment: 3 pages, 4 figures, uses espcrc2.sty, Lattice2003(higgs

    QCD String Spectrum 2002

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    Results from a comprehensive new analysis on the excitation spectrum of the QCD string are presented. A rapid onset of string formation is observed in the spectrum on a length scale of 2 fm, with Dirichlet boundary conditions. The crossover from the short distance spectrum towards string excitations and an observed fine structure in the 1--3 fm range are related to effective string theory. The deficiencies of the Nambu-Goto bosonic string model in describing the observed spectrum are briefly discussed.Comment: Lattice2002(topology), 3 pages, 2 figure

    Excitations of the static quark-antiquark system in several gauge theories

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    The spectrum of gluons in the presence of a static quark-antiquark pair is studied using Monte Carlo simulations on anisotropic space-time lattices. For very small quark-antiquark separations R, the level orderings and approximate degeneracies disagree with the expectations from an effective string theory. As the quark-antiquark separation R increases, a dramatic rearrangement of the energies occurs, and above 2 fm, all of the levels studied show behavior consistent with an effective string description. The energy spacings are nearly pi/R, but a tantalizing fine structure remains. In addition to 4-dimensional SU(3) gauge theory, results from 3-dimensional SU(2) and compact U(1) gauge theories are also presented.Comment: 12 pages, 4 figures, talk presented at the International Conference on Color Confinement and Hadrons in Quantum Chromodynamics (Confinement 2003), RIKEN, July 21-24, 200

    Zero Point Energy of Renormalized Wilson Loops

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    The quark antiquark potential, and its associated zero point energy, can be extracted from lattice measurements of the Wilson loop. We discuss a unique prescription to renormalize the Wilson loop, for which the perturbative contribution to the zero point energy vanishes identically. A zero point energy can arise nonperturbatively, which we illustrate by considering effective string models. The nonperturbative contribution to the zero point energy vanishes in the Nambu model, but is nonzero when terms for extrinsic curvature are included. At one loop order, the nonperturbative contribution to the zero point energy is negative, regardless of the sign of the extrinsic curvature term.Comment: 14 pages, ReVTeX. Paper shortened, results unchange

    The heavy-quark hybrid meson spectrum in lattice QCD

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    Recent findings on the spectrum of heavy-quark mesons from computer simulations of quarks and gluons in lattice QCD are summarized, with particular attention to quark-antiquark states bound by an excited gluon field. The validity of a Born-Oppenheimer treatment for such systems is discussed. Recent results on glueball masses, the light-quark 1-+ hybrid meson mass, and the static three-quark potential are summarized.Comment: 15 pages, 13 figures, talk given at the Workshop on Scalar Mesons: An Interesting Puzzle for QCD, SUNY Institute of Technology, Utica, NY, May 16-18, 2003, submitted to American Institute of Physics Conference Proceedings. After publication, it will be found at http://proceedings.aip.org/proceedings
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