World-Line Actions in Weyl Geometry

Abstract

In this note we construct, from a gauge theory perspective, the world-line action for a particle moving on a time-like curve in Weyl geometry. The action we find is dimensionless, Weyl invariant, additive and, in general, non-local due to an open Wilson line which we have to add in order to account for a general Weyl field. In special cases, this Wilson line can be local, but the geometry becomes integrable. The action can not be used to measure the proper time as it is dimensionless and no mass parameter is allowed in the symmetric phase of the theory. We show that the usual conditions for defining proper time: affine parametrization, dimension of time and additivity supplemented by the requirement of Weyl invariance can not be fulfilled simultaneously and therefore no satisfactory notion of proper time exists in the symmetric phase. Under spontaneous symmetry breaking the particle acquires a mass, the action becomes Riemannian and the proper time can be again defined. We also construct a classically equivalent quadratic action by using an einbein on the world-line and show that the non-locality can be seen to arise from integrating out a constrained field.