821 research outputs found

    Self-consistent theory of turbulence

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    A new approach to the stochastic theory of turbulence is suggested. The coloured noise that is present in the stochastic Navier-Stokes equation is generated from the delta-correlated noise allowing us to avoid the nonlocal field theory as it is the case in the conventional theory. A feed-back mechanism is introduced in order to control the noise intensity.Comment: submitted to J.Tech. Phys.Letters (St. Petersburg

    Leading infrared logarithms for sigma-model with fields on arbitrary Riemann manifold

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    We derive non-linear recursion equation for the leading infrared logarithms (LL) in four dimensional sigma-model with fields on an arbitrary Riemann manifold. The derived equation allows one to compute leading infrared logarithms to essentially unlimited loop order in terms of geometric characteristics of the Riemann manifold. We reduce the solution of the SU(oo) principal chiral field in arbitrary number of dimensions in the LL approximation to the solution of very simple recursive equation. This result paves a way to the solution of the model in arbitrary number of dimensions at N-->ooComment: Talk given by MVP at the conference devoted to memory of A.N. Vasilie

    Coherent interaction of laser pulses in a resonant optically dense extended medium under the regime of strong field-matter coupling

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    Nonstationary pump-probe interaction between short laser pulses propagating in a resonant optically dense coherent medium is considered. A special attention is paid to the case, where the density of two-level particles is high enough that a considerable part of the energy of relatively weak external laser-fields can be coherently absorbed and reemitted by the medium. Thus, the field of medium reaction plays a key role in the interaction processes, which leads to the collective behavior of an atomic ensemble in the strongly coupled light-matter system. Such behavior results in the fast excitation interchanges between the field and a medium in the form of the optical ringing, which is analogous to polariton beating in the solid-state optics. This collective oscillating response, which can be treated as successive beats between light wave-packets of different group velocities, is shown to significantly affect propagation and amplification of the probe field under its nonlinear interaction with a nearly copropagating pump pulse. Depending on the probe-pump time delay, the probe transmission spectra show the appearance of either specific doublet or coherent dip. The widths of these features are determined by the density-dependent field-matter coupling coefficient and increase during the propagation. Besides that, the widths of the coherent features, which appear close to the resonance in the broadband probe-spectrum, exceed the absorption-line width, since, under the strong-coupling regime, the frequency of the optical ringing exceeds the rate of incoherent relaxation. Contrary to the stationary strong-field effects, the density- and coordinate-dependent transmission spectra of the probe manifest the importance of the collective oscillations and cannot be obtained in the framework of the single-atom model.Comment: 10 pages, 8 figures, to be published in Phys. Rev.

    A multiloop improvement of non-singlet QCD evolution equations

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    An approach is elaborated for calculation of "all loop" contributions to the non-singlet evolution kernels from the diagrams with renormalon chain insertions. Closed expressions are obtained for sums of contributions to kernels P(z)P(z) for the DGLAP equation and V(x,y)V(x,y) for the "nonforward" ER-BL equation from these diagrams that dominate for a large value of b0b_0, the first β\beta-function coefficient. Calculations are performed in the covariant ξ\xi-gauge in a MS-like scheme. It is established that a special choice of the gauge parameter ξ=−3\xi=-3 generalizes the standard "naive nonabelianization" approximation. The solutions are obtained to the ER-BL evolution equation (taken at the "all loop" improved kernel), which are in form similar to one-loop solutions. A consequence for QCD descriptions of hard processes and the benefits and incompleteness of the approach are briefly discussed.Comment: 13 pages, revtex, 2 figures are enclosed as eps-file, the text style and figures are corrected following version, accepted for publication to Phys. Rev.

    Measurement of the electron electric dipole moment using GdIG

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    A new method for the detection of the electron edm using a solid is described. The method involves the measurement of a voltage induced across the solid by the alignment of the samples magnetic dipoles in an applied magnetic field, H. A first application of the method to GdIG has resulted in a limit on the electron edm of 5E-24 e-cm, which is a factor of 40 below the limit obtained from the only previous solid-state edm experiment. The result is limited by the imperfect discrimination of an unexpectedly large voltage that is even upon the reversal of the sample magnetization.Comment: 10 pages, 5 figures, v2:references corrected, submitted to PRL, v3:added labels to figure

    An improved \eps expansion for three-dimensional turbulence: two-loop renormalization near two dimensions

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    An improved \eps expansion in the dd-dimensional (d>2d > 2) stochastic theory of turbulence is constructed at two-loop order which incorporates the effect of pole singularities at d→2d \to 2 in coefficients of the \eps expansion of universal quantities. For a proper account of the effect of these singularities two different approaches to the renormalization of the powerlike correlation function of the random force are analyzed near two dimensions. By direct calculation it is shown that the approach based on the mere renormalization of the nonlocal correlation function leads to contradictions at two-loop order. On the other hand, a two-loop calculation in the renormalization scheme with the addition to the force correlation function of a local term to be renormalized instead of the nonlocal one yields consistent results in accordance with the UV renormalization theory. The latter renormalization prescription is used for the two-loop renormalization-group analysis amended with partial resummation of the pole singularities near two dimensions leading to a significant improvement of the agreement with experimental results for the Kolmogorov constant.Comment: 23 pages, 2 figure

    Gauge-invariant critical exponents for the Ginzburg-Landau model

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    The critical behavior of the Ginzburg-Landau model is described in a manifestly gauge-invariant manner. The gauge-invariant correlation-function exponent is computed to first order in the 4−d4-d and 1/n1/n-expansion, and found to agree with the ordinary exponent obtained in the covariant gauge, with the parameter α=1−d\alpha=1-d in the gauge-fixing term (∂μAμ)2/2α(\partial_\mu A_\mu)^2 /2 \alpha.Comment: 4 pages, no figure

    Critical exponents from two-particle irreducible 1/N expansion

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    We calculate the critical exponent ν\nu in the 1/N expansion of the two-particle-irreducible (2PI) effective action for the O(N) symmetric ϕ4\phi ^4 model in three spatial dimensions. The exponent ν\nu controls the behavior of a two-point function {\it near} the critical point T≠TcT\neq T_c, but can be evaluated on the critical point T=TcT=T_c by the use of the vertex function Γ(2,1)\Gamma^{(2,1)}. We derive a self-consistent equation for Γ(2,1)\Gamma^{(2,1)} within the 2PI effective action, and solve it by iteration in the 1/N expansion. At the next-to-leading order in the 1/N expansion, our result turns out to improve those obtained in the standard one-particle-irreducible calculation.Comment: 18 page

    High frequency dielectric and magnetic anomaly at the phase transition in NaV2O5

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    We found anomalies in the temperature dependence of the dielectric and the magnetic susceptibiliy of NaV_2O_5 in the microwave and far infrared frequency ranges. The anomalies occur at the phase transition temperature T_c, at which the spin gap opens. The real parts of the dielectric constants epsilon_a and epsilon_c decrease below T_c. The decrease of epsilon_a (except for the narrow region close to T_c) is proportional to the intensity of the x-ray reflection appearing at T_c. The dielectric constant anomaly can be explained by the zigzag charge ordering in the ab-plane appearing below T_c. The anomaly of the microwave magnetic losses is probably related to the coupling between the spin and charge degrees of freedom in vanadium ladders.Comment: 3 PS-figures, LATEX-text, new experimental data added, typos correcte

    Sequential superradiant scattering from atomic Bose-Einstein condensates

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    We theoretically discuss several aspects of sequential superradiant scattering from atomic Bose-Einstein condensates. Our treatment is based on the semiclassical description of the process in terms of the Maxwell-Schroedinger equations for the coupled matter-wave and optical fields. First, we investigate sequential scattering in the weak-pulse regime and work out the essential mechanisms responsible for bringing about the characteristic fan-shaped side-mode distribution patterns. Second, we discuss the transition between the Kapitza-Dirac and Bragg regimes of sequential scattering in the strong-pulse regime. Finally, we consider the situation where superradiance is initiated by coherently populating an atomic side mode through Bragg diffraction, as in studies of matter-wave amplification, and describe the effect on the sequential scattering process.Comment: 9 pages, 4 figures. Submitted to Proceedings of LPHYS'06 worksho
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