165,031 research outputs found

    A note on brane/flux annihilation and dS vacua in string theory

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    We reconsider the dynamics of p anti-D3 branes inside the Klebanov-Strassler geometry, in which M units of R-R 3-form flux and K units of NS-NS 3-form flux are presented in deformed conifold. We find that anti-D3 branes blow up into a spherical D5-brane at weak string coupling via quantum tunnelling. The D5-brane can be either stable or unstable, depending on number of background flux. The nucleation rate of D5-brane is suppressed by \exp{-Mp^2}. The classical mechanically the evolution of unstable D5-brane annihilates one unit of R-R flux and ends with (K-p) D3-branes. This observation is consistent with one by Kachru, Pearson and Verlinde, who shew that anti-D3 branes in KS geometry can blow up into a spherical NS5 brane at strong string coupling, because NS5-brane is lighter that D5-brane at strong string coupling. We also argue that the system can end with a meta-stable dS vacuum by fine tuning of number of background flux.Comment: 14 pages, 3 eps figures, v2: typos modified and references adde

    Strings in Noncommutative Spacetime

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    Free bosonic strings in noncommutative spacetime are investigated. The string spectrum is obtained in terms of light-cone quantization. We construct two different models. In the first model the critical dimension is still required to be 26 while only extreme high energy spectrum is modified by noncommutative effect. In the second model, however, the critical dimension is reduced to be less than 26 while low-energy (massless) spectrum only contains degrees of freedom of our four dimensional physics.Comment: 9 pages, no figure

    The iterative convolution-thresholding method (ICTM) for image segmentation

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    In this paper, we propose a novel iterative convolution-thresholding method (ICTM) that is applicable to a range of variational models for image segmentation. A variational model usually minimizes an energy functional consisting of a fidelity term and a regularization term. In the ICTM, the interface between two different segment domains is implicitly represented by their characteristic functions. The fidelity term is then usually written as a linear functional of the characteristic functions and the regularized term is approximated by a functional of characteristic functions in terms of heat kernel convolution. This allows us to design an iterative convolution-thresholding method to minimize the approximate energy. The method is simple, efficient and enjoys the energy-decaying property. Numerical experiments show that the method is easy to implement, robust and applicable to various image segmentation models.Comment: 13 pages, 4 figure

    Derivation of Newton's law of gravitation based on a fluidic continuum model of vacuum and a sink flow model of particles

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    The main purpose of this paper is to seek a mechanical interpretation of gravitational phenomena. We suppose that the universe may be filled with a kind of fluid which may be called the Ω(0)\Omega (0) substratum. Thus, the inverse-square law of gravitation is derived by methods of hydrodynamics based on a sink flow model of particles. The first feature of this theory of gravitation is that the gravitational interactions are transmitted by a kind of fluidic medium. The second feature is the time dependence of gravitational constant GG and gravitational mass. Newton's law of gravitation is derived if we introduce an assumption that GG and the masses of particles are changing so slowly that they can be treated as constants.Comment: 8 pages, 0 figures, Revtex

    Nature of Integer Quantum Hall Transitions

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    The mapping between the metal-insulator transition of the quantum Hall system and a superfluid-to-insulator transition is revisited based on a disordered anyon model. The one-parameter scaling of the superfluid-to-insulator transition is employed for the analysis of the scaling behavior of the integer quantum Hall transitions. The analysis reveals the direct transition from a quantum Hall plateau to the insulator in weak disorder limit, and a float-down transition for strong disorders. In either cases, the transition corresponds to a non-chirality superfluid-to-insulator transition, with the longitudinal and transverse quantum Hall conductivities following a semi-circle relation

    Derivation of the Maxwell's Equations Based on a Continuum Mechanical Model of Vacuum and a Singularity Model of Electric Charges

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    We speculate that the universe may be filled with a visco-elastic continuum which may be called aether. Thus, the Maxwell's equations in vacuum are derived by methods of continuum mechanics based on a continuum mechanical model of vacuum and a singularity model of electric charges.Comment: 9 pages, 0 figures, REVTeX

    Derivation of Coulomb's Law of Forces Between Static Electric Charges Based on Spherical Source and Sink Model of Particles

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    We speculate that the universe may be filled with a continuum which may be called aether. Based on a spherical source and sink model of electric charges, we derive Coulomb's law of interactions between static electric charges in vacuum by methods of hydrodynamics. A reduced form of the Lorentz's force law of static electric charges is derived based on a definition of electric field.Comment: 8 pages, 0 figures, Version 4.0 of REVTeX. arXiv admin note: text overlap with arXiv:physics/050606

    Spinning Strings on Deformed AdS_5 x T^{1,1} with NS B-field

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    We study classical spinning closed string configuration on logarithmically deformed AdS_5 x T^{1,1} background with non-trivial Neveu-Schwarz B-field in which IIB string theory is dual to a non-conformal N=1 SU(N+M) x SU(N) gauge theory. The integrability on original AdS_5 x T^{1,1} background are significantly reduced by B-field. We find several spinning string solutions with two different ansatzs. Solutions for point-like strings and few circular strings are explicitly obtained. Folded spinning string solutions along radial direction are shown to be allowed in this background. These solutions exhibit novel properties and bring some challenges to understand them from dual quantum field theory.Comment: 26 pages, v.4: The discussions on folded strings was improve

    Cosmological Constant as Vacuum Energy Density of Quantum Field Theories on Noncommutative Spacetime

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    We propose a new approach to understand hierarchy problem for cosmological constant in terms of considering noncommutative nature of space-time. We calculate that vacuum energy density of the noncommutative quantum field theories in nontrivial background, which admits a smaller cosmological constant by introducing an higher noncommutative scale μNCMp\mu_{NC}\sim M_p. The result ρΛ106ΛSUSY8Mp4/μNC8\rho_\Lambda\sim 10^{-6}\Lambda_{SUSY}^8M_p^4/\mu_{NC}^8 yields cosmological constant at the order of current observed value for supersymmetry breaking scale at 10TeV. It is the same as Banks' phenomenological formula for cosmological constant.Comment: 7 pages, no figures, v4, references adde

    Holography and (1+1)-dimension non-relativistic Quantum Mechanics

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    I generalize classical gravity/quantum gauge theory duality in AdS/CFT correspondence to (1+1)-dimensional non-relativistic quantum mechanical system. It is shown that (1+1)-dimensional non-relativistic quantum mechanical system can be reproduced from holographic projection of (2+1)-dimension classical gravity at semiclassical limit. In this explanation every quantum path in 2-dimension corresponds to a classical path of 3-dimension gravity under definite holographic projection. I consider free particle and harmonic oscillator as two examples and find their dual gravity description.Comment: 4 pages, no fig, use revtex4.cl