Variationality of conformal geodesics in dimension 3

Abstract

Conformal geodesics form an invariantly defined family of unparametrized curves in a conformal manifold generalizing unparametrized geodesics/paths of projective connections. The equation describing them is of third order, and it was an open problem whether they are given by an Euler--Lagrange equation. In dimension 3 (the simplest, but most important from the viewpoint of physical applications) we demonstrate that the equation for unparametrized conformal geodesics is variational.

A remark about conformally invariant Lagrangian is supplied at the end. More references added. Ancillary files can be accessed through version 1