139 research outputs found
A Renormalisation Group Study of Three Dimensional Turbulence
We study the three dimensional Navier-Stokes equation with a random Gaussian
force acting on large wavelengths. Our work has been inspired by Polyakov's
analysis of steady states of two dimensional turbulence. We investigate the
time evolution of the probability law of the velocity potential. Assuming that
this probability law is initially defined by a statistical field theory in the
basin of attraction of a renormalisation fixed point, we show that its time
evolution is obtained by averaging over small scale features of the velocity
potential. The probability law of the velocity potential converges to the fixed
point in the long time regime. At the fixed point, the scaling dimension of the
velocity potential is determined to be . We give conditions for
the existence of such a fixed point of the renormalisation group describing the
long time behaviour of the velocity potential. At this fixed point, the energy
spectrum of three dimensional turbulence coincides with a Kolmogorov spectrum.Comment: 8 pages , tex fil
The Supermoduli Space of Matrix String Theory
We study matrix string scattering amplitudes and matrix string instantons on
a marked Riemann surface in the limit of a vanishing string coupling constant.
We give an explicit parameterization of the moduli space of such instantons. We
also give a description of the set of fermionic supermoduli. The integration
over the supermoduli leads to the inclusion of picture changing operators at
the interaction points. Finally we investigate the large N limit of the measure
on the instanton moduli space and show its convergence to the Weil-Petersson
measure on the moduli space of marked Riemann surfaces.Comment: 30 Pages, Latex, 2 Postscript figure
Open Supermembranes Coupled to M-Theory Five-Branes
We consider open supermembranes in eleven dimensions in the presence of
closed M-Theory five-branes. It has been shown that, in a flat space-time, the
world-volume action is kappa invariant and preserves a fraction of the eleven
dimensional supersymmetries if the boundaries of the membranes lie on the
five-branes. We calculate the reparametrisation anomalies due to the chiral
fermions on the boundaries of the membrane and examine their cancellation
mechanism. We show that these anomalies cancel with the aid of a classical term
in the world-volume action, provided that the tensions of the five-brane and
the membrane are related to the eleven dimensional gravitational constant in a
way already noticed in M-Theory.Comment: Latex, 14 page
Cosmological Evolution on Self-Tuned Branes and the Cosmological Constant
We consider the cosmological evolution of a bulk scalar field and ordinary
matter living on the brane world in the light of the constraints imposed by the
matter dominated cosmological evolution and a small cosmological constant now.
We rule out models with a self-tuned minimum of the four dimensional potential
as they would lead to rapid oscillations of the Hubble parameter now. A more
natural framework is provided by supergravity in singular spaces where the
brane coupling and the bulk potential are related by supersymmetry leading to a
four dimensional run-away potential. For late times we obtain an accelerating
universe due to the breaking of supersymmetry on the brane with an acceleration
parameter of q_0=-4/7 and associated equation of state omega=-5/7.Comment: 24 pages, JHEP styl
Supersymmetric Flat Directions and Analytic Gauge Invariants
We review some aspects of the correspondence between analytic gauge
invariants and supersymmetric flat directions for vanishing D-terms and propose
a criterion to include the F-term constraints.Comment: 8 pages, Late
Models with Inverse Sfermion Mass Hierarchy and Decoupling of the SUSY FCNC Effects
We study the decoupling of the first two squark and slepton families in order
to lower the flavour changing neutral current effects. Models with inverse
sfermion mass hierarchy based upon gauged U(1) flavour symmetries provide a
natural framework where decoupling can be implemented. Decoupling requires a
large gap between the Fermi scale and the supersymmetry breaking scale.
Maintaining the electroweak symmetry breaking at the Fermi scale requires some
fine-tuning that we investigate by solving the two-loop renormalization group
equations. We show that the two-loop effects are governed by the anomaly
compensated by the Green-Schwarz mechanism and can be determined from the quark
and lepton masses. The electroweak breaking constraints lead to a small
scenario where the LSP is Higgsino-like.Comment: 19 pages, Latex, 1 Postscript figur
Quintessence Model Building
A short review of some of the aspects of quintessence model building is
presented. We emphasize the role of tracking models and their possible
supersymmetric origin.Comment: 14 pages, to appear in the proceedings of the sixth workshop of the
American University of Pari
Exponentially Small Couplings between Twisted Fields of Orbifold String Theories
We investigate the natural occurence of exponentially small couplings in
effective field theories deduced from higher dimensional models. We calculate
the coupling between twisted fields of the Z_3 Abelian orbifold
compactification of the heterotic string. Due to the propagation of massive
Kaluza-Klein modes between the fixed points of the orbifold, the massless
twisted fields located at these singular points become weakly coupled. The
resulting small couplings have an exponential dependence on the mass of the
intermediate states and the distance between the fixed points.Comment: 21 pages, 4 figure
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