V.A. Karmanov

Deuteron electromagnetic form factors in the light-front dynamics

The deuteron form factors are calculated in the framework of the relativistic nucleon-meson dynamics, by means of the explicitly covariant light-front approach. The inflluence of the nucleon electromagnetic form factors is discussed. At Q2 < 3 (GeV/c)2 the prediction for the structure function A(Q2) and for the tensor polarization observable t20 are in agreement with the recent data of CEBAF/TJNAF.

Electromagnetic form factors in the light-front dynamics

Abstract It is shown that the electromagnetic vertex of a nucleus (and of any bound system), expressed through the wave function in the light-front dynamics at relativistic values of momentum transfer, contains a contribution of nonphysical form factors which increases the total number of invariant form factors (for the deuteron from 3 up to 11). This fact explains an ambiguity in the form factors calculated previously. The physical and nonphysical form factors are covariantly separated. Explicit expressions for physical form factors of systems with spin 0, 1 2 and 1 through the vertex functions are obtained.

Scattering of low-energy antiprotons from nuclei

Abstract It is shown that the mechanism of low-energy antiproton scattering from nuclei is given by the Glauber model including Coulomb effects. The cross sections for elastic and inelastic (with excitation of nuclear level) p scattering from 12C and 16O and also for elastic scattering from 40Ca and 208Pb are calculated without any free parameters. Calculations are in good agreement with LEAR data. The real-to-imaginary ratios of the p N scattering amplitude are found from antiprotonnucleus cross sections at diffractive minima at energies of 46.8 and 179.7 MeV, which also agree with LEAR values of this ratio. The antiproton-nucleus optical potential and scattering lengths are calculated. Shifts of the 3d levels of the antiproton atoms p 12 C and p 16 O are estimated and are found to be in good agreement with experiment.

Many-body Fock sectors in Wick-Cutkosky model

Abstract In the model where two massive scalar particles interact by the ladder exchanges of massless scalar particles (Wick–Cutkosky model), we study in light-front dynamics the contributions of different Fock sectors (with increasing number of exchanged particles) to full normalization integral and electromagnetic form factor. It turns out that two-body sector always dominates. At small coupling constant α ≪ 1 , its contribution is close to 100%. It decreases with increase of α . For maximal value α = 2 π , corresponding to the zero bound state mass, two-body sector contributes to the normalization integral 64%, whereas the three-body contribution is 26% and the sum of all higher contributions from four- to infinite-body sectors is 10%. Contributions to the form factor from different Fock sectors fall off faster for asymptotically large Q 2 , when the number of particles in the Fock sectors becomes larger. So, asymptotic behavior of the form factor is determined by the two-body Fock sector.

On the calculation of the nucleon electromagnetic form factors in light-front dynamics

Abstract In the formulation of light-front dynamics on the quantization plane t + z = 0, there is an asymmetry between the z- and x-, y-axes that leads in practice to a violation of rotational invariance. In the explicitly covariant formulation of light-front dynamics, the nucleon electromagnetic current matrix elements contain, instead of this violation, additive contributions depending on the position of the light-front plane. We show how to extract the physical form factors, excluding these spurious contributions. We also show why the usual approach, taking into account the J + component of the current only, contains these non-physical contributions. We apply our formalism to a simple three-quark model in order to quantitatively estimate the difference between both approaches. This difference can be as large as 50% at high momentum transfer.

The nucleon wave function in light-front dynamics

The general spin structure of the relativistic nucleon wave function in the 3q-model is found. It contains 16 spin components, in contrast to 8 ones known previously. The explicitly covariant form of the wave function automatically takes into account the relativistic spin rotations, without introducing any Melosh rotation matrices. It also reduces the calculations to the standard routine of the Dirac matrices and of the trace techniques. The importance of investigating the influence of the extra components on the observables is emphasized.

On ambiguities of the spin-1 electromagnetic form factors in light-front dynamics

Abstract In light-front dynamics, different ways of approximately calculating the electromagnetic form factors of any spin-1 system, proceeding from different sets of matrix elements of the J + current component, lead to different form factors. All these ways available in literature are analyzed. The differences between form factors are found analytically in terms of nonphysical contributions coming from the dependence of the electromagnetic vertex on the light-front plane. We show that it is impossible to improve form factors by combining any matrix elements of J + . All the nonphysical contributions are removed, if, in addition to J + , one takes into account other components of the current.

Low-energy antiprotons as a new probe of nuclear reaction mechanism

Abstract The experimental data of LEAR, KEK and BNL on low-energy antiproton interaction with nuclei are analysed in the framework of the Glauber-Sitenko approach. It is shown that antiproton-nucleus interaction gives new information on the nuclear reaction mechanism, on nuclear structure and on parameters of the p N amplitude.

On calculation of the neutron charge radius

We show that the anomalous quark magnetic moments and relativistic effects in the nucleon wave function result in the correct value of the neutron charge radius.

Relativistic effects in deuteron and the reaction D(e,e′p)n

Abstract It is shown that the well known phenomenon — impossibility in principle to separate the center-of-mass motion of a relativistic interacting system from the internal motion - leads to change of the relativistic wave function parametrization in comparison with nonrelativistic case. In its turn this leads to a peak in the D(e, e′p)n cross section measured under special kinematical conditions. This peak can be searched in experiments at new continuous electron beam accelerators.