Item

Abstract

The spin part of angular momentum of the electromagnetic field is known since
the 1990's to be a separately conserved quantity. Cameron et al. introduced the
helicity array, a non-covariant analog of Lipkin's zilch tensor, which
expresses the hierarchy of conservation laws including helicity, spin, as well
as the spin-flux or infra-zilch. In this paper, a novel conserved Lorentz
covariant tensor, termed the helicity tensor, is introduced. The conservation
laws arising from the helicity array can be obtained from the helicity tensor.
The Lorentz covariance of the helicity tensor is in contrast to previous
formulations of the helicity hierarchy of conservation laws, which required the
non-Lorentz covariant transverse gauge. The helicity tensor is shown to arise
as a Noether current for a variational symmetry of a duality-symmetric
Lagrangian for Maxwell theory.