9,618 research outputs found
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 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
- …