Dynamically assisted Schwinger mechanism

TL;DR

Intuitively speaking, the strong electric field lowers the threshold for dynamical particle creation--or, alternatively, the fast electromagnetic field generates additional seeds for the Schwinger mechanism, which could be relevant for planned ultrahigh intensity lasers.

Abstract

We study electron-positron pair creation {from} the Dirac vacuum induced by a strong and slowly varying electric field (Schwinger effect) which is superimposed by a weak and rapidly changing electromagnetic field (dynamical pair creation). In the sub-critical regime where both mechanisms separately are strongly suppressed, their combined impact yields a pair creation rate which is {dramatically} enhanced. Intuitively speaking, the strong electric field lowers the threshold for dynamical particle creation -- or, alternatively, the fast electromagnetic field generates additional seeds for the Schwinger mechanism. These findings could be relevant for planned ultra-high intensity lasers.

Figures (2)

• Figure 1: Sketch (not to scale) of the level structure (top) and the mode functions $u_I^\dagger$ and $v_J$ (bottom). The upper and lower surface of the Dirac sea at $\pm m$ are denoted by solid lines, which are distorted by the electric field $E$ in the interval $-L/2<x<+L/2$ with $qEL= 2m$ (top). The horizontal dotted lines at $\pm\omega$ represent the electron/positron levels $u_I^\dagger$ and $v_J$ with the classical turning points at $x_\pm$.
• Figure 2: Plots of the instanton action [in units of $m^2/(qE)$] for the electric field in (\ref{['cosh']}), computed using the wordline instanton method, and plotted as a function of the combined Keldysh parameter $\gamma$ defined in (\ref{['kel']}). The upper [red] dots correspond to $\omega=100\Omega$ and $E=100 \varepsilon$, while the lower [blue] dots correspond to $\omega=10\Omega$ and $E=10 \varepsilon$. The solid lines show the Schwinger value of $\pi$, estimated in the text to be valid for $\gamma<\pi/2$, and the expression (\ref{['threshold']}), estimated in the text to be valid for $\gamma>\pi/2$. The numerical results agree very well with these estimates in the relevant limit where $E\gg \varepsilon$ and $\omega\gg\Omega$.