Electric and magnetic dipole moments of the bound system of a Dirac particle and a fixed magnetic monopole

Abstract

The electric and the magnetic dipole moments are calculated for the bound states of a charged Dirac particle of spin 1/2 with an extra magnetic moment in the field of a fixed magnetic monopole. Unlike ordinary bound systems with $P$ and/or $T$ invariance, this system, lacking both, is found to possess a nonvanishing electric dipole moment. Its magnitude for the loosely bound states with the lowest possible angular momentum increases exponentially in the principal quantum number $n$. The magnetic moment of the system is found to be, in general, nonvanishing.