27,943 research outputs found

    Nonsingular 4d-flat branes in six-dimensional supergravities

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    We show that six-dimensional supergravity models admit nonsingular solutions in the presence of flat three-brane sources with positive tensions. The models studied in this paper are nonlinear sigma models with the target spaces of the scalar fields being noncompact manifolds. For the particular solutions of the scalar field equations which we consider, only two brane sources are possible which are positioned at those points where the scalar field densities diverge, without creating a divergence in the Ricci scalar or the total energy. These solutions are locally invariant under 1/2 of D=6 supersymmetries, which, however, do not integrate to global Killing spinors. Other branes can be introduced by hand by allowing for local deficit angles in the transverse space without generating any kind of curvature singularities.Comment: 13 pages. The discussion of modular invariance is amended and a reference has been adde

    Solitons in a six-dimensional super Yang-Mills-tensor system and noncritical strings

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    In this letter we study a coupled system of six-dimensional N=1 tensor and super Yang-Mills multiplets. We identify some of the solitonic states of this system which exhibit stringy behaviour in six dimensions. A discussion of the supercharges and energy for the tensor multiplet as well as zero modes is also given. We speculate about the possible relationship between our solution and what is known as tensionless strings.Comment: Plain TeX, 10 page

    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 MĂ—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 MĂ—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
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