Light-fronts approach to electron-positron pair production in ultrarelativistic heavy-ion collisions

We perform a gauge transformation on the time-dependent Dirac equation describing the evolution of an electron in a heavy-ion collision to remove the explicit dependence on the long-range part of the interaction. We solve, in an ultrarelativistic limit, the gauge-transformed Dirac equation using light-front variables and a light-fronts representation, obtaining nonperturbative results for the free pair-creation amplitudes in the collider frame. Our result reproduces the result of second-order perturbation theory in the small charge limit while nonperturbative effects arise for realistic charges of the ions.