Duality and helicity: the photon wave function approach

The photon wave equation proposed in terms of the Riemann-Silberstein vector is derived from a first order Dirac/Weyl-type action principle. It is symmetric w.r.t duality transformations, but the associated Noether quantity vanishes. Replacing the fields by potentials and using instead a quadratic Klein-Gordon type Lagrangian allows us to recover the double-Chem-Simons expression of conserved helicity and is shown to be equivalent to recently proposed alternative frameworks. Applied to the potential-modified theory the Dirac/Weyl-type approach yields again zero conserved charge, whereas the Klein-Gordon-type approach applied to the original setting yields Lipkin's zilch. (C) 2017 Elsevier B.V. All rights reserved.