Alexander Kobushkin

Two-photon exchange in a dispersion approach

We calculate the two-photon exchange amplitude for the elastic electron-proton scattering in the framework of dispersion relations. The imaginary part of the amplitude is determined by unitarity. Since in the unitarity relation intermediate states are on shell, off-shell form factors are not needed for the calculation. The real part is then evaluated using analytical properties of the amplitude. The expression for the elastic contribution to the amplitude, obtained in our approach, differs from the results of traditional calculations with on-shell form factors. Nevertheless, numerically the difference is minor for Q{sup 2} up to 6 GeV{sup 2}.

Box diagram in the elastic electron-proton scattering

We present an evaluation of the box diagram for elastic ep scattering with the proton in the intermediate state. Using analytic properties of the proton form factors we express the amplitude via a twofold integral that involves the form factors in the spacelike region only. Therefore experimentally measured form factors can be used in the calculations directly. The numerical calculation is done with the form factors extracted by Rosenbluth separation, as well as polarization transfer method. The dependence of the results on the form factor choice is small for Q{sup 2}(less-or-similar sign)6 GeV{sup 2} but becomes sizable at higher Q{sup 2}.

Two-photon exchange at low Q 2

We studied two-photon exchange for elastic electron-proton scattering at low Q{sup 2}. Compact approximate formulas for the amplitudes were obtained. Numerical calculations were done for Q{sup 2}{<=}0.1 GeV{sup 2} with several realistic form factor parametrizations, yielding similar results. They indicate that the corrections to the magnetic form factor can visibly affect the cross-section and proton radii. For low-Q{sup 2} electron-neutron scattering two-photon exchange corrections were shown to be negligibly small00.

Phenomenological analysis of two-photon exchange effects in proton form factor measurements

We perform a model-independent phenomenological analysis of experimental data on proton form factor ratio. We find that only one of the two-photon exchange amplitudes, which we call {delta}G{sub M}, is responsible for the discrepancy between Rosenbluth and polarization methods. The linearity of Rosenbluth plots implies that {delta}G{sub M} is approximately linear function of {epsilon}. The slope of {delta}G{sub M} is extracted from experimental data and is shown to be consistent with theoretical calculations.

Beam normal spin asymmetry of elastic eN scattering in the leading logarithm approximation

The beam normal spin asymmetry for elastic eN scattering is studied in the leading logarithm approximation, that is, keeping only terms proportional to

Electro-magnetic waves within a model for charged solitons

\mathrm{ln}{}^{2}{Q}^{2}/{m}^{2},m

Target normal spin asymmetry of the elastic ep scattering at resonance energy

being the electron mass. The resulting expression is valid for a wide range of scattering angles. However, at very forward kinematics the approximation becomes inadequate, and the appropriate conditions are given. We also calculate the numerical values of the asymmetry at intermediate energy and show that they are consistent with existing experimental data. Our results suggest that in the second resonance region multiple-pion intermediate states give a substantial contribution to the asymmetry.

Electrodynamic limit in a model for charged solitons

We analyse the model of topological fermions (MTF), where charged fermions are treated as soliton solutions of the field equations. In the region far from the sources we find plane waves solutions with the properties of electro-magnetic waves.

New Family of Exotic

Bogolyubov Institute for Theoretical PhysicsMetrologicheskaya str. 14-B, 03143, Kiev, Ukraine(Dated: February 9, 2008)We study the target normal spin asymmetry for the reaction ep → ep at electron energy up to fewGeV in the laboratory frame. The asymmetry is proportional to the imaginary part of the reactionscattering amplitude. To estimate the imaginary part of the amplitude we use the unitarity relationand saturate the intermediate hadron states by the proton and resonances from the first, second andthird resonance regions. The resonance electromagnetic transition amplitudes, needed to evaluatethe asymmetry, are taken from experiment.

\Theta

We consider a model of topological solitons where charged particles have finite mass and the electric charge is quantised already at the classical level. In the electrodynamic limit, which physically corresponds to electrodynamics of solitons of zero size, the Lagrangian of this model has two degrees of freedom only and reduces to the Lagrangian of the Maxwell field in dual representation. We derive the equations of motion and discuss their relations with Maxwells equations. It is shown that Coulomb and Lorentz forces are a consequence of topology. Further, we relate the U(1) gauge invariance of electrodynamics to the geometry of the soliton field, give a general relation for the derivation of the soliton field from the field strength tensor in electrodynamics and use this relation to express homogeneous electric fields in terms of the soliton field.