# Franz-Keldysh effect in strong-field QED

## TL;DR

This paper investigates a QED analog of the Franz-Keldysh effect, revealing how a strong slow field combined with a weak field influences particle production, including sub-threshold production and oscillatory behaviors, with implications for experiments.

## Contribution

It introduces the QED Franz-Keldysh effect and analyzes its impact on particle production mechanisms under combined strong and weak fields.

## Key findings

- Perturbative particle production occurs below threshold energy.
- Production peaks just above threshold energy.
- Oscillations appear in production number above threshold.

## Abstract

We studied a QED analog of the Franz-Keldysh effect, and the interplay between the non-perturbative (the Schwinger mechanism) and the perturbative particle production mechanism from the vacuum in the presence of a strong slow field superimposed by a weak field. We found that the Franz-Keldysh effect significantly affects the particle production: (i) the perturbative particle production occurs even below the threshold energy; (ii) the perturbative production becomes the most efficient just above the threshold energy; and (iii) an oscillating behavior appears in the production number above the threshold energy. These non-trivial changes are suppressed only weakly by powers of the critical field strength of QED. A relation to the dynamically assisted Schwinger mechanism and implications to experiments are also discussed.