3,129 research outputs found
Laminar boundary layer in conditions of natural transition to turbulent flow
Results of experimental study of regularities of a natural transition of a laminar boundary layer to a turbulent layer at low subsonic air flow velocities are presented, analyzed and compared with theory and model experiments
Measurement of low turbulence levels with a thermoanemometer
The trend for decreasing the drag of aircraft is retention of laminar flow in the boundary layer over a large portion of the surface. The laminar boundary layer was studied in a low turbulence wind tunnel for low subsonic velocities. The method used and results of measurements of very low levels of turbulence are presented. Measurements were performed by a constant-resistance thermoanemometer
Lie-Algebraic Characterization of 2D (Super-)Integrable Models
It is pointed out that affine Lie algebras appear to be the natural
mathematical structure underlying the notion of integrability for
two-dimensional systems. Their role in the construction and classification of
2D integrable systems is discussed. The super- symmetric case will be
particularly enphasized. The fundamental examples will be outlined.Comment: 6 pages, LaTex, Talk given at the conference in memory of D.V.
Volkov, Kharkhov, January 1997. To appear in the proceeding
Non-Perturbative Green's Functions in Theories with Extended Superconformal Symmetry
The multiplets that occur in four dimensional rigidly supersymmetric theories
can be described either by chiral superfields in Minkowski superspace or
analytic superfields in harmonic superspace. The superconformal Ward identities
for Green's functions of gauge invariant operators of these types are derived.
It is shown that there are no chiral superconformal invariants. It is further
shown that the Green's functions of analytic operators are severely restricted
by the superconformal Ward when analyticity is taken into account.Comment: 17 pages, plain tex. Some conjectures that were in the original paper
are clarifed in the light of more recent work to which we give references.
See Note added for detail
Duality in linearized gravity
We show that duality transformations of linearized gravity in four
dimensions, i.e., rotations of the linearized Riemann tensor and its dual into
each other, can be extended to the dynamical fields of the theory so as to be
symmetries of the action and not just symmetries of the equations of motion.
Our approach relies on the introduction of two "superpotentials", one for the
spatial components of the spin-2 field and the other for their canonically
conjugate momenta. These superpotentials are two-index, symmetric tensors. They
can be taken to be the basic dynamical fields and appear locally in the action.
They are simply rotated into each other under duality. In terms of the
superpotentials, the canonical generator of duality rotations is found to have
a Chern-Simons like structure, as in the Maxwell case.Comment: 10 pages; introduction rewritten and references adde
The \Phi^4 quantum field in a scale invariant random metric
We discuss a D-dimensional Euclidean scalar field interacting with a scale
invariant quantized metric. We assume that the metric depends on d-dimensional
coordinates where d<D. We show that the interacting quantum fields have more
regular short distance behaviour than the free fields. A model of a Gaussian
metric is discussed in detail. In particular, in the \Phi^4 theory in four
dimensions we obtain explicit lower and upper bounds for each term of the
perturbation series. It turns out that there is no coupling constant
renormalization in the \Phi^4 model in four dimensions. We show that in a
particular range of the scale dimension there are models in D=4 without any
divergencies
Brief comments on Jackiw-Teitelboim gravity coupled to Liouville theory
Jackiw-Teitelboim gravity with non-vanishing cosmological constant coupled to
Liouville theory is considered as a non-critical string on dimensional flat
spacetime. It is discussed how the presence of cosmological constant yields
additional constraints on the parameter space of the theory, even when the
conformal anomaly is independent of the cosmological constant. Such constraints
agree with the necessary conditions for the tachyon field to be a primary
--prelogarithmic-- operator of the worldsheet conformal field theory. Thus, the
linearized tachyon field equation allows to impose the diagonal condition for
the interaction term. We analyze the neutralization of the Liouville mode
induced by the coupling to the Jackiw-Teitelboim Lagrangian. The free field
prescription leads to obtain explicit expressions for three-point correlation
functions for the case of vanishing cosmological constant in terms of a product
of Shapiro-Virasoro integrals. This is a consequence of the mentioned
neutralization effect.Comment: 14 pages, no figures. v2 References added. To be published in
Classical and Quantum Gravity. v3 typos correcte
Confinement in Gauge Theories from the Condensation of World-Sheet Defects in Liouville String
We present a Liouville-string approach to confinement in four-dimensional
gauge theories, which extends previous approaches to include non-conformal
theories. We consider Liouville field theory on world sheets whose boundaries
are the Wilson loops of gauge theory, which exhibit vortex and spike defects.
We show that world-sheet vortex condensation occurs when the Wilson loop is
embedded in four target space-time dimensions, and show that this corresponds
to the condensation of gauge magnetic monopoles in target space. We also show
that vortex condensation generates a effective string tension corresponding to
the confinement of electric degrees of freedom. The tension is independent of
the string length in a gauge theory whose electric coupling varies
logarithmically with the length scale. The Liouville field is naturally
interpreted as an extra target dimension, with an anti-de-Sitter (AdS)
structure induced by recoil effects on the gauge monopoles, interpreted as D
branes of the effective string theory. Black holes in the bulk AdS space
correspond to world-sheet defects, so that phases of the bulk gravitational
system correspond to the different world-sheet phases, and hence to different
phases of the four-dimensional gauge theory. Deconfinement is associated with a
Berezinskii-Kosterlitz-Thouless transition of vortices on the Wilson-loop world
sheet, corresponding in turn to a phase transition of the black holes in the
bulk AdS space.Comment: 29 pages LATEX, three eps figures incorporate
Dynamics of Non-Abelian Vortices
The scattering is studied using moduli space metric for well-separated
vortices of non-Abelian vortices in (2+1)-dimensional U(N) gauge theories with
N Higgs fields in the fundamental representation. Unlike vortices in the
Abelian-Higgs model, dynamics of non-Abelian vortices has a lot of new
features; The kinetic energy in real space can be transfered to that of
internal orientational moduli and vice versa, the energy and charge transfer
between two vortices, the scattering angle of collisions with a fixed impact
parameter depends on the internal orientations, and some resonances appear due
to synchronization of the orientations. Scattering of dyonic non-Abelian
vortices in a mass deformed theory is also studied. We find a bound state of
two vortices moving along coils around a circle, like a loop of a phone code.Comment: 45 pages, 13 figure
On the stability problem in the O(N) nonlinear sigma model
The stability problem for the O(N) nonlinear sigma model in the 2+\epsilon
dimensions is considered. We present the results of the 1/N^{2} order
calculations of the critical exponents (in the 2<d<4 dimensions) of the
composite operators relevant for this problem. The arguments in the favor of
the scenario with the conventional fixed point are given.Comment: 9 pages, revtex, 1 Postscript figur
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