We consider a wide class of model equations, able to describe wave propagation in dispersive nonlinear media. The Korteweg-de Vries (KdV) equation is derived in this general frame under some conditions, the physical meanings of which are clarified. It is obtained as usual at leading order in some multiscale expansion. The higher order terms in this expansion are studied making use of a multi-ti...

Abstract We calculate electromagnetic properties of the decuplet baryons in quenched and partially quenched chiral perturbation theory. We work at next-to-leading order in the chiral expansion, leading order in the heavy baryon expansion, and obtain expressions for the magnetic moments, charge radii, and electric quadrupole moments. The quenched calculation is shown to be pathological since onl...

A modification of perturbation theory, known as delta-expansion (variationally improved perturbation), gave rigorously convergent series in some D = 1 models (oscillator energy levels) with factorially divergent ordinary perturbative expansions. In a generalization of variationally improved perturbation appropriate to renormalizable, asymptotically free theories, we show that the large expansio...

The first three coefficients of the Taylor’s series expansion of the vevtor pion form factor as a function of the momentum transfer are evaluated using the experimental data on the pion form factor and the P-wave ππ phase shifts. The real part of the form factor as a function of energy is also calculated by dispersion relation. Comparisons there results with Chiral Perturbation Theory and unita...

We calculated propagation constants of supermodes for two-dimensional two-slab waveguides, with small core gap, using secondorder perturbation expansion from gapless slab waveguide system, and compared our results with the existing works. In the perturbation calculation, we used trapezoidal method to calculate the integral over the transverse direction in space and obtained second-order expansi...

The elastic πN scattering amplitude in the isospin limit is calculated in the framework of heavy baryon chiral perturbation theory, up to the third order. Threshold parameters like scattering lengths, volumes, effective ranges, etc. are compared with data. All relevant low energy constants are fixed from the available pion-nucleon data. A clear improvement in the description of data is observed...

In this talk the Q counting scheme to implement effective field theory is discussed. It is pointed out that there are two small mass scales in the problem mπ and 1/a with 1/a ≪ mπ. It is argued that while the expansion based on 1/a being small compared to the underlying short distance scales works well, the chiral expansion may not. The coefficients of the effective range expansion are sensitiv...

This paper makes the first systematic attempt to determine using perturbation theory the positions of images by gravitational lensing due to arbitrary number of coplanar masses without any symmetry on a plane, as a function of lens and source parameters. We present a method of Taylor-series expansion to solve the lens equation under a small mass-ratio approximation. First, we investigate pertur...

The elastic πN scattering amplitude in the isospin limit is calculated in the framework of heavy baryon chiral perturbation theory, up to the third order. Threshold parameters like scattering lengths, volumes, effective ranges, etc. are compared with data. All relevant low energy constants are fixed from the available pion-nucleon data. A clear improvement in the description of data is observed...

The derivation of effective spin models describing the low energy magnetic properties of undoped CuO 2 –planes is reinvestigated. Our study aims at a quantitative determination of the parameters of effective spin models from those of a multi–band model and is supposed to be relevant to the analysis of recent improved experimental data on the spin wave spectrum of La 2 CuO 4. Starting from a con...