Dissipation of axion energy via the Schwinger and Witten effects

TL;DR

This paper investigates how the interplay of the Witten and Schwinger effects leads to axion energy dissipation and alters its abundance, considering monopoles, dyons, and charged particles in a gauge theory with an anomalous CP phase.

Contribution

It introduces a comprehensive analysis of axion dissipation mechanisms via non-perturbative effects in a monopole-axion system, incorporating the back reaction on axion dynamics.

Findings

Axion oscillations can dissipate energy through Schwinger pair production near dyons.

The effective potential of the axion is modified by the Witten effect and pair production.

Electric dipole radiation can be emitted from monopole-anti-monopole bound states due to axion oscillations.

Abstract

In the presence of an anomalous CP phase in a U(1) gauge theory, a monopole becomes a dyon via the Witten effect. When the anomalous CP phase is promoted to a dynamical field, the axion, the electric charge of the dyon changes according to the coherent motion of the axion oscillation. Once the electric charge exceeds a certain threshold, the Schwinger pair production of charged particles becomes efficient near the surface of the dyon. These non-perturbative effects lead to the back reaction of the axion dynamics by causing the dissipation of the axion oscillation energy and the change of the effective potential due to the Witten effect. Taking these effects into account, we consider the dynamics of the whole system, including the axion, monopole, and charged heavy vector bosons, and discuss to what extent the axion abundance is modified. We also discuss the electric dipole radiation from a bound state of a monopole-anti-monopole pair due to the axion coherent oscillations.