909 research outputs found
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
Ne quid nimis” o “Non satis”. Peripecias del “hecho dogmático” y de la “fe eclesiástica”"
«Status quaestionis». Algunos estudios del presente siglo. Primera etapa: desde
la Edad Media hasta el siglo XVI. Segundo período: del siglo XVII al siglo XIX. Tercer
período: desde el Vaticano I hasta hoy. Conclusión
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
Les usages en ligne du patrimoine écrit : du partage à l'enrichissement de contenus
En 2006, le catalogue des collections patrimoniales numérisées élaboré par le ministère de la Culture, Patrimoine numérique, recense près de 1 150 fonds ou collections numérisés. On sait peu que 44 % de ce patrimoine désormais numérique proviennent des archives départementales et 27 % des bibliothèques municipales, ce qui place ces deux services culturels locaux largement devant tous les autres. Cette constatation liminaire invite à poser la question des patrimoines écrits numériques en Pays-de-la-Loire, des conditions de son avènement comme des modalités de ses usages.
L’impact du numérique dans le champ du patrimoine écrit n’a pas encore produit tous ses effets et le système n’a pas encore trouvé son équilibre. Des effets attendus ne sont pas avérés, comme l’affirmation de la notion de patrimoine écrit susceptible de transcender les périmètres professionnels et d’élargir les publics. D’autres, inattendus ou sous-estimés, jouent à plein, comme la redéfinition de la relation entre les institutions patrimoniales et leurs publics et l’irruption du secteur privé dans les modalités de diffusion des données publiques, y compris patrimoniales
Convergent sequences of perturbative approximations for the anharmonic oscillator; 1, 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
Differential equation for four-point correlation function in Liouville field theory and elliptic four-point conformal blocks
Liouville field theory on a sphere is considered. We explicitly derive a
differential equation for four-point correlation functions with one degenerate
field . We introduce and study also a class of four-point
conformal blocks which can be calculated exactly and represented by finite
dimensional integrals of elliptic theta-functions for arbitrary intermediate
dimension. We study also the bootstrap equations for these conformal blocks and
derive integral representations for corresponding four-point correlation
functions. A relation between the one-point correlation function of a primary
field on a torus and a special four-point correlation function on a sphere is
proposed
Exact 1/N and Optimized Perturbative Evaluation of mu_c for Homogeneous Interacting Bose Gases
In the framework of the O(N) three-dimensional effective scalar field model
for homogeneous dilute weakly interacting Bose gases we use the 1/N expansion
to evaluate, within the large N limit, the parameter r_c which is directly
related to the critical chemical potential mu_c. This quantity enters the
order-a^2 n^{2/3} coefficient contributing to the critical temperature shift
Delta T_c where a represents the s-wave scattering length and n represents the
density. Compared to the recent precise numerical lattice simulation results,
our calculation suggests that the large N approximation performs rather well
even for the physical case N=2. We then calculate the same quantity but using
different forms of the optimized perturbative (variational) method, showing
that these produce excellent results both for the finite N and large-N cases.Comment: 12 pages, 2 figures. We have performed a refined and extended
numerical analysis to take into account the very recent results of Ref. [15
Vacuum Values for Auxiliary String Fields
Auxiliary string fields are introduced in light-cone gauge string field
theory in order to express contact interactions as contractions of cubic
vertices. The auxiliary field in the purely closed-string bosonic theory may be
given a non-zero expectation value, leading to a phase in which world-sheets
have boundaries.Comment: 13 pages, DAMTP/94-2
A new improved optimization of perturbation theory: applications to the oscillator energy levels and Bose-Einstein critical temperature
Improving perturbation theory via a variational optimization has generally
produced in higher orders an embarrassingly large set of solutions, most of
them unphysical (complex). We introduce an extension of the optimized
perturbation method which leads to a drastic reduction of the number of
acceptable solutions. The properties of this new method are studied and it is
then applied to the calculation of relevant quantities in different
models, such as the anharmonic oscillator energy levels and the critical
Bose-Einstein Condensation temperature shift recently investigated
by various authors. Our present estimates of , incorporating the
most recently available six and seven loop perturbative information, are in
excellent agreement with all the available lattice numerical simulations. This
represents a very substantial improvement over previous treatments.Comment: 9 pages, no figures. v2: minor wording changes in title/abstract, to
appear in Phys.Rev.
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