Two-photon exchange at low Q^2

We study two-photon exchange for elastic electron-proton scattering at low Q^2. Compact approximate formulae for the amplitudes are obtained. Numerical calculations are done for Q^2 < 0.1 GeV^2 with several realistic form factor parameterizations, yielding similar results. They indicate that the corrections to magnetic form factor can visibly affect cross-section and proton radii. For low-Q^2 electron-neutron scattering two-photon exchange corrections are shown to be negligibly small.Comment: 5 pages, 4 figure

Two-photon exchange amplitudes for the elastic epep scattering at Q^2=2.5 GeV^2 from the experimental data

We extract two-photon exchange amplitudes for the elastic electron-proton scattering at Q^2=2.5 GeV^2 from the unpolarized cross-section and recent polarization transfer measurements. There are three independent amplitudes, but only one of them, \delta G_M, can be determined with a reasonable accuracy(about 10%). The result is in good agreement with theoretical predictions. Rough estimates for two other amplitudes are obtained.Comment: 3 pages, 3 figure

Generalization of multifractal theory within quantum calculus

On the basis of the deformed series in quantum calculus, we generalize the partition function and the mass exponent of a multifractal, as well as the average of a random variable distributed over self-similar set. For the partition function, such expansion is shown to be determined by binomial-type combinations of the Tsallis entropies related to manifold deformations, while the mass exponent expansion generalizes the known relation $\tau_q=D_q(q-1)$. We find equation for set of averages related to ordinary, escort, and generalized probabilities in terms of the deformed expansion as well. Multifractals related to the Cantor binomial set, exchange currency series, and porous surface condensates are considered as examples. Keywords:Multifractal set; Deformation; Power series.Comment: 12 pages, 4 figures, accepted by EP

Proton charge and magnetic rms radii from the elastic epep scattering data

The elastic electron-proton scattering data are analysed in order to determine proton charge and magnetic rms radii, r_E and r_M. Along with the usual statistical error, we try to estimate a systematic error in the radii, caused by the inadequacy of particular form factor parameterization employed. The range of data to use in the analysis is chosen so as to minimize the total (statistical + systematic) error. We obtain r_E = 0.912 +- 0.009 (stat) +- 0.007 (syst) fm, and r_M = 0.876 +- 0.010 (stat) +- 0.016 (syst) fm. The cross-section data were corrected for two-photon exchange. We found that without such corrections obtained r_E and r_M are somewhat smaller while the quality of fit is worse.Comment: 6 pages, 4 figures. Numbers slightly changed due to discovered error in minimization program. Sec.III revised, discussion of G_E behaviour added