# Real-time dynamics of axion particle production due to spontaneous decay of a coherent axion field

## TL;DR

This paper investigates how a coherent axion field can spontaneously decay into axion particles through quantum tunneling, providing a formalism to analyze the real-time dynamics and backreaction effects.

## Contribution

The authors develop a novel formalism using $$-expansion and mean field approximation to study real-time axion particle production and backreaction.

## Key findings

- Demonstrated spontaneous decay of axion field via quantum tunneling.
- Provided numerical results on axion particle production and energy density evolution.
- Discussed phenomenological implications of axion decay dynamics.

## Abstract

We show that the coherent axion field spontaneously decays by emitting axion particles via quantum tunneling if axion potential has more than one minimum. By employing the $\hbar$-expansion and mean field approximation, we develop a formalism to trace the real-time dynamics of the axion particle production including its backreaction to the coherent axion field. We also present numerical results for the time evolution of various physical quantities including the strength of the coherent axion field, phase-space density of produced axion particles, energy density, and pressure. Phenomenological implications of our results are also discussed.