Solving Noether's equations for gauge invariant local Lagrangians of N   arbitrary higher even spin fields
  We consider systems of higher spin gauge fields that are described by a free field Lagrangian and one interaction of arbitrary order $N$ that is local and satisfies abelian gauge invariance. Such "solitary" interactions are derived from Noether potentials solving the Noether equations. They are constructed using a free conformal field theory carried by the same flat space as the higher spin fields. In this field theory we consider $N$-loop functions of conserved, conformally covariant currents, they are UV divergent. The residue of the first order pole in the dimensional regularisation approach to the $N$-loop function is a local differential operator and is free of anomalies, so that current conservation and conformal covariance is maintained. Applying this operator to the higher spin fields, the Noether potential results. We study the cases $N=2, N=3$ and N=4. We argue that our N=3 vertex for any number of derivatives $\Delta$ is identical with the known cubic interaction. 
Werner Ruehl
hep-th