1,741 research outputs found
A new determination of from Renormalization Group Optimized Perturbation
A new version of the so-called optimized perturbation (OPT), implementing
consistently renormalization group properties, is used to calculate the
nonperturbative ratio of the pion decay constant and
the basic QCD scale in the scheme. Using the experimental
input value it provides a new determination of for
and , and of the QCD coupling constant at
various scales once combined with a standard perturbative evolution. The
stability and empirical convergence properties of the RGOPT modified series is
demonstrated up to the third order. We examine the difference sources of
theoretical uncertainties and obtain , where the first errors are
estimates of the intrinsic theoretical uncertainties of our method, and the
second errors come from present uncertainties in , where is
in the exact chiral limit.Comment: 5 pages, talk given at EPS-HEP, Stockholm, Sweden 18-24 July, 201
Convergent sequences of perturbative approximations for the anharmonic oscillator II. Compact time approach
We present an alternative pathway in the application of the variation
improvement of ordinary perturbation theory exposed in [1] which can preserve
the internal symmetries of a model by means of a time compactification.Comment: 21 pages, 4 Postscript figures available through anonymous ftp at
ftp://algol.lpm.univ-montp2.fr ; replaces version which could not be
postscripted presumably for lack of figures.uu fil
Convergent sequences of perturbative approximations for the anharmonic oscillator I. Harmonic approach
We present numerical evidence that a simple variational improvement of the
ordinary perturbation theory of the quantum anharmonic oscillator can give a
convergent sequence of approximations even in the extreme strong coupling
limit, the purely anharmonic case. Some of the new techniques of this paper can
be extended to renormalizable field theories.Comment: 29 pages, 12 Postscript figures available through anonymous ftp at
ftp://algol.lpm.univ-montp2.fr ; replaces earlier version which could not be
postscripted presumably due to lack of figures.uu fil
Photonic Hall Effect in ferrofluids: Theory and Experiments
An experimental and theoretical study on the Photonic Hall Effect (PHE) in
liquid and gelled samples of ferrofluids is presented. The ferrofluids are
aqueous colloidal suspensions of Fe(_{2})CoO(_{4}) particles, which can be
considered as anisotropic and absorbing Rayleigh scatterers.
The PHE is found to be produced by the orientation of the magnetic moments of
the particles, as is also the case for the Faraday effect. The dependence of
the PHE with respect to the concentration of the scatterers, the magnetic field
and the polarization of the incident light is measured in liquid and in gelled
samples and is compared to a simple model based on the use of a scattering
matrix and the single scattering approximation.Comment: 20 pages, 11 figures, submitte
On off-shell bosonic string amplitudes
We give a simple prescription for computing, in the framework of the bosonic
string theory, off-shell one-loop amplitudes with any number of external
massless particles, both for the open and for the closed string. We discuss
their properties and, in particular, for the two-string one-loop amplitudes we
show their being transverse.Comment: 12 pages, Latex. One reference added. Introduction and conclusions
expanded. Some other minor changes in the tex
Almost Sure Convergence of Solutions to Non-Homogeneous Stochastic Difference Equation
We consider a non-homogeneous nonlinear stochastic difference equation
X_{n+1} = X_n (1 + f(X_n)\xi_{n+1}) + S_n, and its important special case
X_{n+1} = X_n (1 + \xi_{n+1}) + S_n, both with initial value X_0, non-random
decaying free coefficient S_n and independent random variables \xi_n. We
establish results on \as convergence of solutions X_n to zero. The necessary
conditions we find tie together certain moments of the noise \xi_n and the rate
of decay of S_n. To ascertain sharpness of our conditions we discuss some
situations when X_n diverges. We also establish a result concerning the rate of
decay of X_n to zero.Comment: 22 pages; corrected more typos, fixed LaTeX macro
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