1,552 research outputs found
Lagrangian Particle Statistics in Turbulent Flows from a Simple Vortex Model
The statistics of Lagrangian particles in turbulent flows is considered in
the framework of a simple vortex model. Here, the turbulent velocity field is
represented by a temporal sequence of Burgers vortices of different
circulation, strain, and orientation. Based on suitable assumptions about the
vortices' statistical properties, the statistics of the velocity increments is
derived. In particular, the origin and nature of small-scale intermittency in
this model is investigated both numerically and analytically
The strong-CP question in SU(3)_c X SU(3)_L X U(1)_N models
We analyze two recent models based on the gauge group
SU(3)SU(3)U(1) where each generation is not
anomaly-free, but anomaly cancels when three generations are taken into
account. We show that the most general Yukawa couplings of these models admit
of a Peccei-Quinn symmetry. This symmetry can be extended to the entire
Lagrangian by using extra fields in a very elegant way so that the resulting
axion can be made invisible.Comment: Latex, 8 pages, no figure
Scaling of the superconducting transition temperature in underdoped high-Tc cuprates with a pseudogap energy: Does this support the anyon model of their superfluidity?
In earlier work, we have been concerned with the scaling properties of some
classes of superconductors, specifically with heavy Fermion materials and with
five bcc transition metals of BCS character. Both of these classes of
superconductors were three-dimensional but here we are concerned solely with
quasi-two-dimensional high-Tc cuprates in the underdoped region of their phase
diagram. A characteristic feature of this part of the phase diagram is the
existence of a pseudogap (pg). We therefore build our approach around the
assumption that kB Tc / E_pg is the basic dimensionless ratio on which to
focus, where the energy E_pg introduced above is a measure of the pseudogap.
Since anyon fractional statistics apply to two-dimensional assemblies, we
expect the fractional statistics parameter allowing `interpolation' between
Fermi-Dirac and Bose-Einstein statistical distribution functions as limiting
cases to play a significant role in determining kB Tc / E_pg and experimental
data are analyzed with this in mind.Comment: Phys. Chem. Liquids, to be publishe
The Lundgren-Monin-Novikov Hierarchy: Kinetic Equations for Turbulence
We present an overview of recent works on the statistical description of
turbulent flows in terms of probability density functions (PDFs) in the
framework of the Lundgren-Monin-Novikov (LMN) hierarchy. Within this framework,
evolution equations for the PDFs are derived from the basic equations of fluid
motion. The closure problem arises either in terms of a coupling to multi-point
PDFs or in terms of conditional averages entering the evolution equations as
unknown functions. We mainly focus on the latter case and use data from direct
numerical simulations (DNS) to specify the unclosed terms. Apart from giving an
introduction into the basic analytical techniques, applications to
two-dimensional vorticity statistics, to the single-point velocity and
vorticity statistics of three-dimensional turbulence, to the temperature
statistics of Rayleigh-B\'enard convection and to Burgers turbulence are
discussed.Comment: Accepted for publication in C. R. Acad. Sc
Hawking Radiation from Charged Black Holes via Gauge and Gravitational Anomalies
Extending gr-qc/0502074, we show that in order to avoid a breakdown of
general covariance and gauge invariance at the quantum level the total flux of
charge and energy in each outgoing partial wave of a charged quantum field in a
Reissner-Nordstrom black hole background must be equal to that of a (1+1)
dimensional blackbody at the Hawking temperature with the appropriate chemical
potential.Comment: 4 pages, typos corrected, references added, version to appear in
Phys. Rev. Let
Classical Dynamics of Anyons and the Quantum Spectrum
In this paper we show that (a) all the known exact solutions of the problem
of N-anyons in oscillator potential precisely arise from the collective degrees
of freedom, (b) the system is pseudo-integrable ala Richens and Berry. We
conclude that the exact solutions are trivial thermodynamically as well as
dynamically.Comment: 19 pages, ReVTeX, IMSc/93/0
The Renormalization Group, Systems of Units and the Hierarchy Problem
In the context of the Renormalization Group (RG) for gravity I discuss the
role of field rescalings and their relation to choices of units. I concentrate
on a simple Higgs model coupled to gravity, where natural choices of units can
be based on Newton's constant or on the Higgs mass. These quantities are not
invariant under the RG, and the ratio between the units is scale-dependent. In
the toy model, strong RG running occurs in the intermediate regime between the
Higgs and the Planck scale, reproducing the results of the Randall-Sundrum I
model. Possible connections with the problem of the mass hierarchy are pointed
out.Comment: Plain TEX, 16 pages. Some revisions, some references adde
Theory for the single-point velocity statistics of fully developed turbulence
We investigate the single-point velocity probability density function (PDF)
in three-dimensional fully developed homogeneous isotropic turbulence within
the framework of PDF equations focussing on deviations from Gaussianity. A
joint analytical and numerical analysis shows that these deviations may be
quantified studying correlations of dynamical quantities like pressure
gradient, external forcing and energy dissipation with the velocity. A
stationary solution for the PDF equation in terms of these quantities is
presented, and the theory is validated with the help of direct numerical
simulations indicating sub-Gaussian tails of the PDF.Comment: 6 pages, 4 figures, corrected typo in eq. (4
Incompressible fluid inside an astrophysical black hole?
It is argued that under natural hypothesis the Fermions inside a black hole
formed after the collapse of a neutron star could form a non compressible fluid
(well before reaching the Planck scale) leading to some features of integer
Quantum Hall Effect. The relations with black hole entropy are analyzed.
Insights coming from Quantum Hall Effect are used to analyze the coupling with
Einstein equations. Connections with some cosmological scenarios and with
higher dimensional Quantum Hall Effect are shortly pointed out.Comment: 30 pages, 2 figures. Accepted for publication on Physical Review D:
references added, typos corrected, test polishe
Axion Cosmology and the Energy Scale of Inflation
We survey observational constraints on the parameter space of inflation and
axions and map out two allowed windows: the classic window and the inflationary
anthropic window. The cosmology of the latter is particularly interesting;
inflationary axion cosmology predicts the existence of isocurvature
fluctuations in the CMB, with an amplitude that grows with both the energy
scale of inflation and the fraction of dark matter in axions. Statistical
arguments favor a substantial value for the latter, and so current bounds on
isocurvature fluctuations imply tight constraints on inflation. For example, an
axion Peccei-Quinn scale of 10^16 GeV excludes any inflation model with energy
scale > 3.8*10^14 GeV (r > 2*10^(-9)) at 95% confidence, and so implies
negligible gravitational waves from inflation, but suggests appreciable
isocurvature fluctuations.Comment: 10 PRD pages, 4 figs, V3: updated to match published versio
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