Cross-helicity effects and turbulent transport in magnetohydrodynamic flow

In the presence of large-scale vortical motions and/or magnetic-field strains, the turbulent cross helicity (velocity--magnetic-field correlation in fluctuations) may contribute to the turbulent electromotive force and the Reynolds stress. These effects of cross helicity are considered to balance the primary effects of turbulence such as the turbulent magnetic diffusivity in magnetic-field evolution and the eddy viscosity in the momentum transport. The cross-helicity effects may suppress the enhanced transports due to turbulence. Physical interpretation of the effects is presented with special emphasis on the difference between the cross-helicity effect and the usual $\alpha$ or helicity effect in the dynamo action. The relative importance of the cross-helicity effect in dynamo action is validated with the aid of a direct numerical simulation (DNS) of the Kolmogorov flow with an imposed magnetic field. Several mechanisms that provide turbulence with the cross helicity are also discussed.Comment: 10 pages, 6 figures, Journal of Physics Conference Series: 13th European Turbulence Conference (ETC13

Near horizon superconformal symmetry of rotating BPS black holes in five dimensions

We investigate the asymptotic supersymmetry group of the near horizon region of the BMPV black holes, which are the rotating BPS black holes in five dimensions. When considering only bosonic fluctuations, we show that there exist consistent boundary conditions and the corresponding asymptotic symmetry group is generated by a chiral Virasoro algebra with the vanishing central charge. After turning on fermionic fluctuations with the boundary conditions, we also show that the asymptotic supersymmetry group is generated by a chiral super-Virasoro algebra with the vanishing central extension. The super-Virasoro algebra is originated in the AdS2 isometry supergroup of the near horizon solution.Comment: 25 pages, Latex, no figure; references adde

Operator Formulation of Green-Schwarz Superstring in the Semi-Light-Cone Conformal Gauge

In this article we present a comprehensive account of the operator formulation of the Green-Schwarz superstring in the semi-light-cone (SLC) gauge, where the worldsheet conformal invariance is preserved. Starting from the basic action, we systematically study the symmetry structure of the theory in the SLC gauge both in the Lagrangian and the phase space formulations. After quantizing the theory in the latter formulation we construct the quantum Virasoro and the super-Poincare generators and clarify the closure properties of these symmetry algebras. Then by making full use of this knowledge we will be able to construct the BRST-invariant vertex operators which describe the emission and the absorption of the massless quanta and show that they form the appropriate representation of the quantum symmetry algebras. Furthermore, we will construct an exact quantum similarity transformation which connects the SLC gauge and the familiar light-cone (LC) gauge. As an application BRST-invariant DDF operators in the SLC gauge are obtained starting from the corresponding physical oscillators in the LC gauge.Comment: 88 pages, ptptex, no figure. Some clarifications are made and a reference is added in section 6. Published versio

Renormalization Group Flow near the Superconformal Points in N=2 Supersymmetric Gauge Theories

The behavior of the beta-function of the low-energy effective coupling in the N=2 supersymmetric SU(2) QCD with several massive matter hypermultiplets and in the SU(3) Yang-Mills theory is determined near the superconformal points in the moduli space. The renormalization group flow is unambiguously fixed by looking at limited types of deformation near the superconformal points. It is pointed out that the scaling dimension of the beta-function is controlled by the scaling behavior of moduli parameters and the relation between them is explicitly worked out. Our scaling dimensions of the beta-functions are consistent in part with the results obtained recently by Bilal and Ferrari in a different method for the SU(2) QCD.Comment: 16 pages, latex, no figure, some references adde