Electromagnetic helicity flux density for radiative systems

Abstract: The electromagnetic (EM) helicity flux density and the magnetic helicity are related by topological Chern-Simons terms. We show that the helicity flux density is distinguished from magnetic helicity by analysing Hopf solitons. We find the helicity flux density for a point charge moving with an acceleration, extending the Li\'enard-Wiechert angular distribution of radiant power. We also derive the multipole expansion of the helicity flux density, generalizing the Larmor's formula for the radiant power. These formulae have been applied to discuss the helicity flux density in several toy models such as circular and helical motion as well as soft bremsstrahlung. We also comment on the potential applications of the EM helicity flux density to pulsar systems.