Pair production in the quantum Boltzmann equation

A source term in the quantum Boltzmann equation, which accounts for the spontaneous creation of ${\mathit{e}}^{+}$ ${\mathit{e}}^{\mathrm{-}}$ pairs in external electric fields, is derived from first principles and evaluated numerically. Careful analysis of time scales reveals that this source term is generally non-Markovian. This implies in particular that there may be temporary violations of the H theorem.