We reconsider QED radiative corrections (RC) to the π 0 → e + e − decay width. One kind of RC investigated earlier has a renormalization group origin and can be associated with the final state interaction of electron and positron. It determines the distribution of lepton pair invariant masses in the whole kinematic region. The other type of RC has a double-logarithmic character and is related to almost on-mass-shell behavior of the lepton form factors. The total effect of RC for the π 0 → e + e − decay is estimated to be 3.2% and for the decay η → e + e − is 4.3%.

The cross section for polarized and unpolarized electron-proton scattering is calculated taking into account radiative corrections in leading and next-to leading logarithmic approximation. The expression of the cross section is formally similar to the cross section of the Drell-Yan process, where the structure functions of the electron play the role of Drell-Yan probability distributions. The interference of the Born amplitude with the two photon exchange amplitude (box-type diagrams) is expressed as a contribution to K-factor and it is larger when the momentum is equally shared between the two photons, assuming that proton form factors decrease rapidly with the momentum transfer squared. The calculation of the box amplitude is done when the intermediate state is a proton or the ∆-resonance. The results of numerical estimations show that the present calculation of radiative corrections can bring into agreement the conflicting experimental results on proton electromagnetic form factors an that the two photon contribution is very small. PACS numbers:

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20 pages, 7 figures 2 tablesWorld data on the lepton-charge asymmetry in the elastic and inelastic lepton scattering off the proton and nuclei are compiled and discussed. After reviewing the published results, we compare the elastic data to a model calculation of the two-photon exchange mechanism. We show that the existing data do not provide any evidence for the two-photon contribution. At significance level 0.05 the data allow to exclude the two-photon exchange as an explanation for the difference between Rosenbluth and polarization measurements of proton electromagnetic form factors

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The processes of muons (tau) and charged pions pairs production at electronpositron annihilation with O(α) radiative corrections are considered. The calculation results are presented assuming the energies of final particles (cms implied) to be not far significantly from threshold production. The invariant mass distributions for the muon (tau) and pion pairs are obtained both for the initial and final state radiation.Some analytical calculations are illustrated numerically. The pions were assumed to be point-like objects and scalar QED was applied for calculation. The QED radiative corrections related to the final state radiation, additional to the well known Coulomb factor, are treated near threshold region exactly.

Two kinds of asymmetry arise from the interference of the Born amplitude and the box-type amplitude corresponding to two virtual photons exchange, namely charge-odd and one spin asymmetries. In case of unpolarized particles the charge-odd correlation is calculated. It can be measured in combination of electron muon and positron muon scattering experiments. The forward-backward asymmetry is the corresponding quantity which can be measured for the crossed processes. In the case of polarized muon the one-spin asymmetry for annihilation and scattering channels has been calculated. The additional structure function arising from the interference is shown to suffer from infrared divergencies. The background due to electroweak interaction is discussed. PACS numbers:

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