# Axion-like-particle decay in strong electromagnetic backgrounds

## TL;DR

This paper calculates the decay probabilities of axion-like particles into electron-positron pairs in strong electromagnetic fields, revealing different regimes and oscillatory behaviors depending on particle mass and field strength, with implications for experimental detection.

## Contribution

It provides a detailed analysis of decay processes in strong fields, including non-perturbative tunnelling and oscillatory effects, extending understanding beyond previous perturbative approaches.

## Key findings

- Decay probability depends on quantum nonlinearity parameter and particle mass.
- Below-threshold decay involves non-perturbative tunnelling exponent.
- Above-threshold decay exhibits nonlinear oscillations around spontaneous decay rate.

## Abstract

The decay of a massive pseudoscalar, scalar and U(1) boson into an electron-positron pair in the presence of strong electromagnetic backgrounds is calculated. Of particular interest is the constant-crossed-field limit, relevant for experiments that aim to measure high-energy axion-like-particle conversion into electron-positron pairs in a magnetic field. The total probability depends on the quantum nonlinearity parameter - a product of field and lightfront momentum invariants. Depending on the seed particle mass, different decay regimes are identified. In the below-threshold case, we find the probability depends on a non-perturbative tunnelling exponent depending on the quantum parameter and the particle mass. In the above-threshold case, we find that when the quantum parameter is varied linearly, the probability oscillates nonlinearly around the spontaneous decay probability. A strong-field limit is identified in which the threshold is found to disappear. In modelling the fall-off of a quasi-constant-crossed magnetic field, we calculate probabilities beyond the constant limit and investigate when the decay probability can be regarded as locally constant.