General analysis of polarization phenomena in e++e-->N+N-bar for axial parametrization of two-photon exchange

General properties of the differential cross section and of the polarization observables are derived for the e++e-->N+N-bar reaction, in presence of two-photon exchange. Polarization effects are investigated for longitudinally polarized electron and polarized antinucleon and/or polarized nucleon in the final state. The single-spin asymmetry induced by the transverse polarization of the electron beam is also discussed