Electron-positron pair production in a bifrequent oscillating electric field

The spontaneous creation of electron-positron pairs in a strong external electric field is a remarkable nonperturbative phenomenon, intrinsically associated with the instability of the quantum vacuum [1–3]. In a constant electric field, this phenomenon–also known as the Schwinger mechanism–has a production rate exponentially small ∼ exp(−πEc/E). Hence, its occurrence is expected to be difficult to achieve experimentally, unless the electric field strength E comes close to the critical scale of quantum electrodynamics (QED) Ec = 1.3×10 16 V/cm. Unfortunately, a field of such a nature is not within the reach of current technical capabilities and a direct experimental observation of the Schwinger mechanism remains a big challenge for the contemporary physics. Hopes of reaching the required field strengths in the focal spot of envisaged high-intensity lasers such as the Extreme Light Infrastructure (ELI) [4] and the Exawatt Center for Extreme Light Studies (XCELS) [5] have renewed the interest in the study of Schwinger-like pair production (PP) processes. Its verification will provide significant insights in the nonlinear QED regime as well as in various processes which share its nonperturbative feature. Notably, among them are the Unruh and Hawking radiation and the string breaking in the theory of the strong interactions [6]. While the prospect of using the strong field of lasers is enticing from practical perspectives, there exists a price to be paid for: the complicated nature of the electromagnetic field of a laser pulse–the wave profile, its spacetime dependence and the existence of magnetic field components–introduces considerable additional complications in the calculations associated with the PP process. Indeed, it seems that a full description of the vacuum decay in such a scenario is far from being compu