Lepton-pair production in relativistic ion collisions and its correspondence to the crossing process

Using the Sudakov technique, we sum the perturbation series for the process 3 → 3 and obtain the compact analytical expression for the amplitude of this process, which takes into account all possible Coulomb interactions between colliding particles. Comparing it to the amplitude of the lepton-pair production in heavy-ion collisions, i.e., in the process 2 → 4, we show that the amplitudes obtained in the high-energy limit lose the crossing-symmetry property (which holds only on the Born level).