Fermion pair production in QED and the backreaction problem in (1+1)-dimensional boost-invariant coordinates revisited

We study two different initial conditions for fermions for the problem of pair production of fermions coupled to a classical electromagnetic field with backreaction in (1 + 1)-dimensional boost-invariant coordinates. Both of these conditions are consistent with fermions initially in a vacuum state. We present results for the proper-time evolution of the electric field E, the current J, the matter energy density epsilon, and the pressure p as a function of the proper time for these two cases. We also determine the interpolating number density as a function of the proper time. We find that when we use a "first-order adiabatic'' vacuum initial condition or a "free-field'' initial condition for the fermion field, we obtain essentially similar behavior for physically measurable quantities. The second method is computationally simpler, it is twice as fast and involves half the storage required by the first method.