On the Finsler variational nature of autoparallels in metric-affine geometry
Lehel Csillag, Nicoleta Voicu, Salah Elgendi, Christian Pfeifer
Abstract
In metric-affine geometry, autoparallels are generically non-variational, i.e., they are not extremals of any action integral. The existence of a parameter-invariant action principle for autoparallels is a longstanding open problem, which is equivalent to the so-called Finsler metrizability of the connection, i.e., to the fact that these autoparallels can be interpreted as Finsler geodesics. In this article, we address this problem for the class of torsion-free affine connections with vectorial nonmetricity, which includes, as notable subcases, Weyl and Schrödinger connections. For this class, we determine the necessary and sufficient conditions for the existence of a Finsler Lagrangian that metrizes the connection and depends only algebraically on it. In the cases where such a Finsler Lagrangian exists, we construct it explicitly. In particular, we show that a broad class of such connections is Finsler metrizable.
