Criticality and dominance of axion physics in highly magnetized vacuum

TL;DR

This paper explores how axion-like particles influence quantum vacuum properties in strong magnetic fields, revealing significant modifications to photon behavior and Coulomb potential, with implications for neutron star magnetospheres and fundamental physics.

Contribution

It provides a second-order calculation of the axion-induced self-energy in a magnetic field, extending understanding of vacuum fluctuations and photon propagation in axion-electrodynamics.

Findings

Axion effects dominate over electron-positron fluctuations in strong magnetic fields.

Photon propagation and Coulomb potential are significantly altered by axion interactions.

Unbounded hydrogen ground-state energy in strong fields is regularized by axion physics.

Abstract

In a constant and homogeneous magnetic background, quantum vacuum fluctuations due to axion-like fields can dominate over those associated with the electron-positron fields. Considering the framework of axion-electrodynamics, the self-energy operator for the electromagnetic field is determined with an accuracy to second-order in the axion-diphoton coupling. This outcome is utilized for establishing modifications to the propagation characteristics of photons and to the Coulomb potential of a static pointlike charge. Notably, in the magnetosphere of a neutron star, the effect of photon capture by the magnetic field, known in QED as relating to gamma-quanta, is extended in axion electrodynamics to include X-ray photons with the result that a specially polarized part of the heat radiation from the surface is canalized along the magnetic field. Besides, for field strengths larger than the critical scale associated with this theory, the modified Coulomb potential is of Yukawa-type in the direction perpendicular to the magnetic field at distances much smaller than the Compton wavelength of an axion, while along the field it follows approximately the Coulomb law at any length scale. We find that at unlimitedly large magnetic fields the longstanding problem -- overcome in QED -- that the ground-state energy of a hydrogen atom is unbounded from below, is reinstated. However, in axion-electrodynamics this unboundedness is cut off because the largest magnetic field treatable within this theory is limited by the unitarity of the associated scattering matrix.