We investigate the effect of high order radiative corrections in unpolarized electron proton elastic scattering and compare with the calculations at lowest order, which are usually applied to experimental data. Particular attention is devoted to the
$epsilon$ dependence of radiative corrections, which is directly related to the electric proton form factor. We consider in particular the effects of the interference terms for soft and hard photon emission. Both quadratic amplitude describing the collinear emission along the scattered electron as well as the interference with the amplitudes of emission from the initial electron and the emission from protons are important in leading and next to leading approximation and they may compensate in particular kinematical conditions.
The high energy amplitudes of the large angles Moller scattering are calculated in frame of chiral basis in Born and 1-loop QED level. Taking into account as well the contribution from emission of soft real photons the compact relations free from inf
rared divergences are obtained. The expressions for separate chiral amplitudes contribution to the cross section are in agreement with renormalization group predictions.
The s-channel annihilation of proton and antiproton into a neutral pion and a real or virtual photon followed by lepton pair emission is studied. Such mechanism is expected to play a role at moderate values of the total energy $sqrt{s}$, when the pio
n is emitted around $90^{circ}$ in the center of mass. A fair comparison with the existing data is obtained taking into account scattering and annihilation channels. The cross section is calculated and numerical results are given in the kinematical range accessible in the PANDA experiment at FAIR.
The process of two pion production in the electron-polarized proton scattering is investigated. In the Weizsacker-Williams approximation the differential spectral distributions and the spin-momentum correlations are considered. The spin correlation e
ffects caused by $rho$-meson widths are estimated to be of an order of several per cent. Both channels of the $pi^+pi^-$ and $pi^+pi^0$ creation are considered. The effects of intermediate excited baryons are not considered. The spectral distributions on pion energy fractions in polarized and unpolarized cases are presented analytically and numerically.
The charge pion polarizability is calculated in the Nambu-Jona-Lasinio model, where the quark loops (in the mean field approximation) and the meson loops (in the $1/N_c$ approximation) are taken into account. We show that quark loop contribution domi
nates, because the meson loops strongly conceal each other. The sigma-pole contribution $(m^2_sigma-t)^{-1}$ plays the main role and contains strong t-dependence of the effective pion polarizability at the region $|t|geq 4M_pi^2$. Possibilities of experimental test of this sigma-pole effect in the reaction of Coulomb Nuclear Scattering are estimated for the COMPASS experiment.
The final state interaction of pions in the decay $K^pmto pi^+pi^-e^pm u$ allows to obtain the value of the isospin and angular momentum zero pion-pion scattering length $a_0^0$. To extract this quantity from experimental data the radiative correctio
ns (RC) have to be taken into account. Basing on the lowest order results and the factorization hypothesis, we get the expressions for RC in the leading and next-to leading logarithmical approximation. It is shown that the decay width dependence on the lepton mass $m_e$ through the parameter $sigma=frac{alpha}{2pi}br{lnfrac{M^2}{m_e^2}-1}$ has a standard form of the Drell-Yan process and is proportional to the Sommerfeld-Sakharov factor. The numerical estimations are presented.
The cross sections of the scalar meson $f_0(980)$, $a_0(980)$ and $sigma(600)$ production in collision of electron and positron beams were calculated. The two-photon decays of the scalar mesons, obtained in the framework of the Nambu-Jona-Lasinio mod
el, were used. The quark and meson loops were taken into account.
The two-photon decay widths of scalar mesons sigma(600), f_0(980) and a_0(980) as well a_0 -> rho(omega)gamma and f_0 -> rho(omega)gamma are calculated in the framework of the local Nambu-Jona-Lasinio model. The contributions of the quark loops (Hart
ree-Fock approximation) and the meson loops (next 1/Nc -approximation where Nc is the number of colors) are taken into account. These contributions, as we show, are the values of the same order of magnitude. For the f_0 decay the K-loop contribution turns out to play the dominant role. The results for two-gamma decays are in satisfactory agreement with modern experimental data. The predictions for a_0 -> rho(omega)gamma and f_0 -> rho(omega)gamma widths are given.
Using the description of the subprocess $gammagamma^*to S(P)$ in terms of local Nambu-Jona-Lasinio model we calculate the cross sections of photoproduction of scalar and pseudoscalar mesons in high energy photon-lepton collisions processes. The depen
dence on the transversal momentum and the total cross sections in Weizsaecker-Williams approximation are presented.
The two-photon decay widths of scalar mesons sigma(600), f_0(980) and a_0(980) are calculated in framework of the local Nambu-Jona-Lasinio model. The contributions of the quark loops (Hartree-Fock approximation) and the meson loops (next 1/N_c-approx
imation where N_c is the number of colors) are taken into account. These contributions, as we show, are the values of the same order of magnitude. For the f_0 decay the K-loop contribution turns out to play the dominant role. The results are in satisfactory agreement with modern experimental data.
