Generalized helicity and Beltrami fields Original Research Article

We propose covariant and non-abelian generalizations of the magnetic helicity and Beltrami equation. The gauge invariance, variational principle, conserved current, energy–momentum tensor and choice of boundary conditions elucidate the subject. In particular, we prove that any extremal of the Yang–Mills action functional image subject to the local constraint image satisfies the covariant non-abelian Beltrami equation.