20,561 research outputs found

    Magnetic Field and Curvature Effects on Pair Production I: Scalars and Spinors

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    The pair production rates for spin-zero and spin-12\frac{1}{2} particles are calculated on spaces of the form M×R1,1M \times {\mathbb R}^{1,1} with MM corresponding to R2{\mathbb R}^2 (flat), T2T^2 (flat, compactified), S2S^2 (positive curvature) and H2H^2 (negative curvature), with and without a background magnetic field on MM. The motivation is to elucidate the effects of curvature and background magnetic field. Contrasting effects for positive and negative curvature on the two cases of spin are obtained. For positive curvature, we find enhancement for spin-zero and suppression for spin-12\frac{1}{2}, with the opposite effect for negative curvature.Comment: 28 pages, 10 figure

    Magnetic Field and Curvature Effects on Pair Production II: Vectors and Implications for Chromodynamics

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    We calculate the pair production rates for spin-11 or vector particles on spaces of the form M×R1,1M \times {\mathbb R}^{1,1} with MM corresponding to R2{\mathbb R}^2 (flat), S2S^2 (positive curvature) and H2H^2 (negative curvature), with and without a background (chromo)magnetic field on MM. Beyond highlighting the effects of curvature and background magnetic field, this is particularly interesting since vector particles are known to suffer from the Nielsen-Olesen instability, which can dramatically increase pair production rates. The form of this instability for S2S^2 and H2H^2 is obtained. We also give a brief discussion of how our results relate to ideas about confinement in nonabelian theories.Comment: 24 pages, 9 figure

    The Isospin Asymmetry in Anomalous Fluid Dynamics

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    The dynamics of fluids in which the constituent particles carry nonabelian charges can be described succinctly in terms of group-valued variables via a generalization of the co-adjoint orbit action for particles. This formalism, which is particularly suitable for incorporating anomalies, has previously been used for the chiral magnetic and chiral vorticity effects. Here we consider the similar effect for the isospin which corresponds to an angular asymmetry for neutral pions.Comment: 12 page

    Plasmon interactions in the quark-gluon plasma

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    Yang-Mills theory at finite temperature is rewritten as a theory of plasmons which provides a Hamiltonian framework for perturbation theory with resummation of hard thermal loops.Comment: 12 pages, LaTeX, minor typos corrected, discussion adde

    Control Synthesis for an Underactuated Cable Suspended System Using Dynamic Decoupling

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    This article studies the dynamics and control of a novel underactuated system, wherein a plate suspended by cables and with a freely moving mass on top, whose other ends are attached to three quadrotors, is sought to be horizontally stabilized at a certain height, with the ball positioned at the center of mass of the plate. The freely moving mass introduces a 2-degree of underactuation into the system. The design proceeds through a decoupling of the quadrotors and the plate dynamics. Through a partial feedback linearization approach, the attitude of the plate and the translational height of the plate is initially controlled, while maintaining a bounded velocity along the yy and xx directions. These inputs are then synthesized through the quadrotors with a backstepping and timescale separation argument based on Tikhonov's theorem

    Effective Theory of Wilson Lines and Deconfinement

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    To study the deconfining phase transition at nonzero temperature, I outline the perturbative construction of an effective theory for straight, thermal Wilson lines. Certain large, time dependent gauge transformations play a central role. They imply the existence of interfaces, which can be used to determine the form of the effective theory as a gauged, nonlinear sigma model of adjoint matrices. Especially near the transition, the Wilson line may undergo a Higgs effect. As an adjoint field, this can generate eigenvalue repulsion in the effective theory.Comment: 6 pages, LaTeX. Final, published version. Refs. 7, 39, and 40 added. In Ref. 37, there is an expanded discussion of a "fuzzy" bag mode

    Supersymmetry and Mass Gap in 2+1 Dimensions: A Gauge Invariant Hamiltonian Analysis

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    A Hamiltonian formulation of Yang-Mills-Chern-Simons theories with 0≤N≤40\leq N\leq 4 supersymmetry in terms of gauge-invariant variables is presented, generalizing earlier work on nonsupersymmetric gauge theories. Special attention is paid to the volume measure of integration (over the gauge orbit space of the fields) which occurs in the inner product for the wave functions and arguments relating it to the renormalization of the Chern-Simons level number and to mass-gaps in the spectrum of the Hamiltonians are presented. The expression for the integration measure is consistent with the absence of mass gap for theories with extended supersymmetry (in the absence of additional matter hypermultiplets and/or Chern-Simons couplings), while for the minimally supersymmetric case, there is a mass-gap, the scale of which is set by a renormalized level number, in agreement with indications from existing literature. The realization of the supersymmetry algebra and the Hamiltonian in terms of the gauge invariant variables is also presented.Comment: 31 pages, References added, typos correcte

    Fuzzy spaces and new random matrix ensembles

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    We analyze the expectation value of observables in a scalar theory on the fuzzy two sphere, represented as a generalized hermitian matrix model. We calculate explicitly the form of the expectation values in the large-N limit and demonstrate that, for any single kind of field (matrix), the distribution of its eigenvalues is still a Wigner semicircle but with a renormalized radius. For observables involving more than one type of matrix we obtain a new distribution corresponding to correlated Wigner semicircles.Comment: 12 pages, 1 figure; version to appear in Phys. Rev.
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