Strong CP Violation in External Magnetic Fields

TL;DR

This paper investigates how strong CP violation affects the QCD vacuum in external magnetic fields, predicting vacuum polarization and electric dipole moments that could influence astrophysical phenomena like magnetars and neutron stars.

Contribution

It introduces a theoretical analysis of QCD vacuum response to magnetic fields under CP violation using chiral perturbation theory and large N_c expansion, highlighting potential astrophysical implications.

Findings

Magnetic fields induce vacuum polarization and electric dipole moments.

Polarization could accelerate charges to energies around 10^3 TeV.

Potential link to hot-spots on neutron star surfaces.

Abstract

We study the response of the QCD vacuum to an external magnetic field, in the presence of strong CP violation. Using chiral perturbation theory and large N_c expansion, we show that the external field would polarize quantum fluctuations and induce an electric dipole moment of the vacuum, along the direction of the magnetic field. We estimate the magnitude of this effect in different physical scenarios. In particular, we find that the polarization induced by the magnetic field of a magnetar could accelerate electric charges up to energies of the order \theta 10^3 TeV. We also suggest a connection with the possible existence of "hot-spots" on the surface of neutron stars.