Relativistic instant-form approach to the structure of two-body composite systems

A new approach to the electroweak properties of two-particle composite systems is developed. The approach is based on the use of the instant form of relativistic Hamiltonian dynamics. The main novel feature of this approach is the new method of construction of the matrix element of the electroweak current operator. The electroweak current matrix element satisfies the relativistic covariance conditions and in the case of the electromagnetic current also the conservation law automatically. The properties of the system as well as the approximations are formulated in terms of form factors. The approach makes it possible to formulate relativistic impulse approximation in such a way that the Lorentz-covariance of the current is ensured. In the electromagnetic case the current conservation law is ensured, too. The results of the calculations are unambiguous: they do not depend on the choice of the coordinate frame and on the choice of "good" components of the current as it takes place in the standard form of light--front dynamics. Our approach gives good results for the pion electromagnetic form factor in the whole range of momentum transfers available for experiments at present time, as well as for lepton decay constant of pion.Comment: 26 pages, Revtex, 5 figure

Isgur--Wise function in a relativistic model of constituent quarks

The integral representation for Isgur -- Wise function (IWF) is obtained in the framework of instant--form relativistic Hamiltonian dynamics for mesons with one heavy quark. The upper and lower limits are calculated for the slope parameter of IWF $\rho^2$ by the model independent way. IWF is calculated for different wave functions of quarks in the meson. The difference between the limits of $\rho^2$ equals 1/3. The constraint on the slope parameter is in a good agreement with experiments. The weak dependence of IWF on the choice of wave functions is found.Comment: 10 pages, latex, 1 figure as eps-fil

Form factors in RQM approaches: constraints from space-time translations

Different relativistic quantum mechanics approaches have recently been used to calculate properties of various systems, form factors in particular. It is known that predictions, which most often rely on a single-particle current approximation, can lead to predictions with a very large range. It was shown that accounting for constraints related to space-time translations could considerably reduce this range. It is shown here that predictions can be made identical for a large range of cases. These ones include the following approaches: instant form, front form, and "point-form" in arbitrary momentum configurations and a dispersion-relation approach which can be considered as the approach which the other ones should converge to. This important result supposes both an implementation of the above constraints and an appropriate single-particle-like current. The change of variables that allows one to establish the equivalence of the approaches is given. Some points are illustrated with numerical results for the ground state of a system consisting of scalar particles.Comment: 37 pages, 7 figures; further comments in ps 16 and 19; further references; modified presentation of some formulas; corrected misprint

RQM description of the charge form factor of the pion and its asymptotic behavior

The pion charge and scalar form factors, $F_1(Q^2)$ and $F_0(Q^2)$, are first calculated in different forms of relativistic quantum mechanics. This is done using the solution of a mass operator that contains both confinement and one-gluon-exchange interactions. Results of calculations, based on a one-body current, are compared to experiment for the first one. As it could be expected, those point-form, and instant and front-form ones in a parallel momentum configuration fail to reproduce experiment. The other results corresponding to a perpendicular momentum configuration (instant form in the Breit frame and front form with $q^+=0$) do much better. The comparison of charge and scalar form factors shows that the spin-1/2 nature of the constituents plays an important role. Taking into account that only the last set of results represents a reasonable basis for improving the description of the charge form factor, this one is then discussed with regard to the asymptotic QCD-power-law behavior $Q^{-2}$. The contribution of two-body currents in achieving the right power law is considered while the scalar form factor, $F_0(Q^2)$, is shown to have the right power-law behavior in any case. The low-$Q^2$ behavior of the charge form factor and the pion-decay constant are also discussed.}Comment: 30 pages, 10 figure

Poincaré-invariant constituent quark model for light mesons: capabilities and constraints

We present a brief survey of some results on electroweak properties of com- posite systems that are obtained in the frameworks of our version of the instant form of relativistic quantum mechanics (RQM). Our approach describes well the π- and the ρ- mesons in wide range of momentum transfers Q2. At large Q2 the obtained pion form factor asymptotics coincides with that of QCD predictions. The method permits to per- form analytic continuation of pion form factor to complex plane of momentum transfers that is in accordance with predictions of quantum field theory

Electroweak properties of

Charge and magnetic radii, magnetic and quadrupole moments of the ρ-meson are calculated in framework of the developed by authors version of the instant form of relativistic quantum mechanics with fixed number of particles (IF RQM). The calculations are performed with different wave functions of quarks in the ρ-meson and using the so- called modified impulse approximation (MIA). The electromagnetic characteristics of ρ-meson are obtained without fitting parameters. The value of the magnetic moment coincides with available experimental data: μρ = 2.1 ± 0.5 e/2Mρ

Mathematical modeling of fiber-optic electric field sensor with FBG based on electret

В настоящее время к одним из наиболее эффективных преобразователей, отвечающих высоким требованиям по метрологическим и эксплуатационным показателям, относятся волоконно-оптические. В статье отражено современное состояние измерительных волоконно-оптических датчиков, рассмотрены основные типы и методы измерения. Предложена новая модель волоконно-оптического датчика на основе решеток Брегга для измерения электрических параметров. Для предложенной модели рассчитана математическая модель. Получены результаты работы и проведена их оценка. Currently, one of the most effective converters that meet the high requirements for metrological and operational parameters are fiber-optic. The article reflects the current state of fiber-optic sensors, considers the main types and methods of measurement. The proposed new model of fiber-optic sensor based on Bragg gratings for measuring electrical parameters. A mathematical model is calculated for the proposed model. The results of the work were obtained and evaluated

Method of calculation of electroweak characteristics of mesons in the poincaré invariant quantum mechanics

На основе точечной формы пуанкаре-инвариантной квантовой механики в работе представлена методика вычисления форм факторов и констант распадов мезонов, как релятивистских связанных систем кварков. В качестве примера разработанной методики получено интегральное представление константы радиационного распада векторного мезона VP.On the basis of the point form of Poincaré-invariant quantum mechanics, a method for calculating the formsfactors and the decay constants of mesons, as relativistic coupled quark systems,is presented. As an example of the developed technique, an integral representation of the radiative decay constant of a vectormeson VPis obtained