Helicity amplitudes for the small-angle process e−e±→e−γγ+e± with both photons along one direction and its cross channel Original Research Article

We study the small-angle double bremsstrahlung in e−e± scattering for a jet kinematics where both photons move along the electron direction. This region gives the main contribution to the cross section. We present analytic expressions for all 64 amplitudes with arbitrary helicity states of the initial and final leptons and the produced photons convenient for analytic and numerical studies. The accuracy of the obtained amplitudes is given omitting only terms of the order of m2/Ej2, θj2 and θjm/Ej. The helicity amplitudes for the cross channel γe±→γe+e−+e± are given. Several limits for the helicity amplitudes of hard or soft final particles are considered.