14,666 research outputs found

    Perturbative Confinement

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    A Procedure is outlined that may be used as a starting point for a perturbative treatment of theories with permanent confinement. By using a counter term in the Lagrangian that renormalizes the infrared divergence in the Coulomb potential, it is achieved that the perturbation expansion at a finite value of the strong coupling constant may yield reasonably accurate properties of hadrons, and an expression for the string constant as a function of the QCD Lambda parameter.Comment: Presented at QCD'02, Montpellier, July 2002. 12 pages LaTeX, 8 Figures PostScript, uses gthstyle.sty Reprt-no: ITF-2002/39; SPIN-2002/2

    TransPlanckian Particles and the Quantization of Time

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    Trans-Planckian particles are elementary particles accelerated such that their energies surpass the Planck value. There are several reasons to believe that trans-Planckian particles do not represent independent degrees of freedom in Hilbert space, but they are controlled by the cis-Planckian particles. A way to learn more about the mechanisms at work here, is to study black hole horizons, starting from the scattering matrix Ansatz. By compactifying one of the three physical spacial dimensions, the scattering matrix Ansatz can be exploited more efficiently than before. The algebra of operators on a black hole horizon allows for a few distinct representations. It is found that this horizon can be seen as being built up from string bits with unit lengths, each of which being described by a representation of the SO(2,1) Lorentz group. We then demonstrate how the holographic principle works for this case, by constructing the operators corresponding to a field in space-time. The parameter t turns out to be quantized in Planckian units, divided by the period R of the compactified dimension.Comment: 12 pages plain tex, 1 figur

    Geometry of Scattering at Planckian Energies

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    We present an alternative derivation and geometrical formulation of Verlinde topological field theory, which may describe scattering at center of mass energies comparable or larger than the Planck energy. A consistent trunckation of 3+1 dimensional Einstein action is performed using the standard geometrical objects, like tetrads and spin connections. The resulting topological invariant is given in terms of differential forms.Comment: 8

    Winding Solutions for the two Particle System in 2+1 Gravity

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    Using a PASCAL program to follow the evolution of two gravitating particles in 2+1 dimensions we find solutions in which the particles wind around one another indefinitely. As their center of mass moves `tachyonic' they form a Gott-pair. To avoid unphysical boundary conditions we consider a large but closed universe. After the particles have evolved for some time their momenta have grown very large. In this limit we quantize the model and find that both the relevant configuration variable and its conjugate momentum become discrete.Comment: 15 pages Latex, 4 eps figure

    Can Electro-Weak \h-Term be Observable ?

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    We rederive and discuss the result of the previous paper that in the standard model θ\theta-term related to WW-boson field can not be induced by weak instantons. This follows from the existence of the fermion zero mode in the instanton field even when Yukawa couplings are switched on and there are no massless particles. We consider the new index theorem connecting the topological charge of the weak gauge field with the number of fermion zero modes of a certain differential operator which depends not only on gauge but also on Higgs fields. The possible generalizations of the standard model are discussed which lead to nonvanishing weak θ\theta-term. In SU(2)L×SU(2)RSU(2)_L \times SU(2)_R model the θ\theta dependence of the vacuum energy is computed.Comment: 21 pages, Preprint TPI-MINN-93/24-

    Quantization of Space and Time in 3 and in 4 Space-time Dimensions

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    The fact that in Minkowski space, space and time are both quantized does not have to be introduced as a new postulate in physics, but can actually be derived by combining certain features of General Relativity and Quantum Mechanics. This is demonstrated first in a model where particles behave as point defects in 2 space dimensions and 1 time, and then in the real world having 3+1 dimensions. The mechanisms in these two cases are quite different, but the outcomes are similar: space and time form a (non-cummutative) lattice. These notes are short since most of the material discussed in these lectures is based on two earlier papers by the same author (gr-qc/9601014 and gr-qc/9607022), but the exposition given in the end is new.Comment: Lectures held at the NATO Advanced Study Institute on ``Quantum Fields and Quantum Space Time", Carg\`ese, July 22 -- August 3, 1996. 16 pages Plain TeX, 6 Figure

    Thermal photon dispersion law and modified black-body spectra

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    Based on the postulate that photon propagation is governed by an SU(2) gauge principle we numerically compute the one-loop dispersion for thermalized photon propagation on the radiatively induced mass shell. Formerly, the dispersion was addressed by assuming p2=0p^2=0. While this approximation turns out to be excellent for temperatures ≤2TCMB\le 2 T_{\tiny{CMB}} the exact result exhibits a much faster (power-like) shrinking of the gap in the black-body spectral intensity with rising temperature. Our previous statements on anomalous large-angle CMB temperature-temperature correlations, obtained in the approximation p2=0p^2=0, remain valid.Comment: v2: 13 pages, 6 figures; sec. 2.1. added to explain effective theory; references added; matches journal published versio

    Pauli-Lubanski scalar in the Polygon Approach to 2+1-Dimensional Gravity

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    In this paper we derive an expression for the conserved Pauli-Lubanski scalar in 't Hooft's polygon approach to 2+1-dimensional gravity coupled to point particles. We find that it is represented by an extra spatial shift Δ\Delta in addition to the usual identification rule (being a rotation over the cut). For two particles this invariant is expressed in terms of 't Hooft's phase-space variables and we check its classical limit.Comment: Some errors are corrected and a new introduction and discussion are added. 6 pages Latex, 4 eps-figure

    Are magnetic monopoles hadrons?

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    The charges of magnetic monopoles are constrained to a multiple of 2Ď€2\pi times the inverse of the elementary unit electric charge. In the standard model, quarks have fractional charge, raising the question of whether the basic magnetic monople unit is a multiple of 2Ď€/e2 \pi/e or three times that. A simple lattice construction shows how a magnetic monopole of the lower strength is possible if it interacts with gluonic fields as well. Such a monopole is thus a hadron. This is consistent with the construction of magnetic monopoles in grand unified theories.Comment: Poster presented at Lattice2004(topology), Fermilab, June 21-26, 2004. 3 pages, 5 figure

    Heavy meson semileptonic decays in two dimensions in the large Nc

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    We study QCD in 1+1 dimensions in the large Nc limit using light-front Hamiltonian perturbation theory in the 1/Nc expansion. We use this formalism to exactly compute hadronic transition matrix elements for arbitrary currents at leading order in 1/Nc, which we use to write the semileptonic differential decay rate of a heavy meson and its moments. We then compare with the results obtained using an effective field theory approach based on perturbative factorization, with the intention of better understanding quark-hadron duality. A very good numerical agreement is obtained between the exact result and the result using effective theories.Comment: Talk given at the High-Energy Physics International Conference on Quantum Chromodynamics, 3-7 July (2006), Montpellier (France
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