Role of the spatial inhomogeneity on the laser-induced vacuum decay

Abstract

This study suggests that the unavoidable spatial inhomogeneity of intense electromagnetic fields has a drastic effect on the electron-positron pair creation process from the vacuum. We use the example of the Breit-Wheeler process, where the collision of two gamma-ray photons is predicted to create electron-positron pairs, to show that the multi-photon pair creation process cannot be modeled by solutions to the Dirac equation under time-periodic fields that are spatially homogeneous. The neglect of the spatial inhomogeneity leads here to spurious energy spectra and misleading pair creation yields that can be incorrect by up to several orders in magnitude. This finding is surprising as there are many widely cited works where the laser is modeled by a spatially homogeneous alternating electric field.

Dynamically assisted Schwinger effect beyond the spatially-uniform-field approximation

“…Finally, we stress that the spatial dependence of the external background in the context of Schwinger pair production was considered so far in a very few studies [16,17,20,[26][27][28]. We expect that multidimensional inhomogeneities should be significant for a much broader class of possible scenarios.…”

“…After completion of the present investigation we noticed the very recent study [16], where it was demonstrated that the spatial dependence of the external field plays a crucial role in the context of the Breit-Wheeler process, where a combination of two fast-varying laser pulses is considered. It was shown that one can hardly approximate the resulting field of two pulses with large γ by a spatially uniform background.…”

“…First, one can examine pulses of a finite size instead of two infinite pulses forming a standing wave. According to the recent studies [16,17], the coordinate dependence of the envelope function can play a very important role, especially in the case of short laser pulses. Besides, in many studies of various scenarios within the dipole approximation, it was demonstrated that the momentum spectra of particles and other characteristics can be very sensitive to changes in the shape of the laser pulse (see, e.g., Refs.…”

“…The essential point is that the Schwinger effect has never been observed experimentally as the required field strength is extremely large. In the case of a static and spatially uniform electric field, the characteristic critical field strength is E c ¼ m 2 c 3 =ðjejℏÞ ≈ 1.3 × 10 16 V=cm which is 3 − 4 orders of magnitude larger than the peak electric field strength reached in modern laser pulses. Nevertheless, the laser technologies develop very rapidly, so one may expect the Schwinger mechanism to become experimentally accessible in the not too distant future.…”

Perturbative methods for assisted nonperturbative pair production

“…where Σ 3 is given by (51). We show in Appendix B how to obtain (62) with the worldline-momentum approach.…”