General Relativity and Weyl Geometry

TL;DR

This paper reformulates general relativity within Weyl geometry, revealing invariance under Weyl transformations and establishing connections with scalar-tensor theories like Brans-Dicke, offering new perspectives on gravitational phenomena.

Contribution

It introduces a Weyl geometric formalism for general relativity, demonstrating invariance under Weyl transformations and linking it to scalar-tensor theories such as Brans-Dicke.

Findings

General relativity can be expressed as a Weyl-invariant scalar-tensor theory.

Different Weyl frames can lead to distinct physical interpretations of the same phenomena.

WIST gravity theories are equivalent to Brans-Dicke theory in specific frames.

Abstract

We show that the general theory of relativity can be formulated in the language of Weyl geometry. We develop the concept of Weyl frames and point out that the new mathematical formalism may lead to different pictures of the same gravitational phenomena. We show that in an arbitrary Weyl frame general relativity, which takes the form of a scalar-tensor gravitational theory, is invariant with respect to Weyl tranformations. A kew point in the development of the formalism is to build an action that is manifestly invariant with respect to Weyl transformations. When this action is expressed in terms of Riemannian geometry we find that the theory has some similarities with Brans-Dicke gravitational theory. In this scenario, the gravitational field is not described by the metric tensor only, but by a combination of both the metric and a geometrical scalar field. We illustrate this point by, firstly, discussing the Newtonian limit in an arbitrary frame, and, secondly, by examining how distinct geometrical and physical pictures of the same phenomena may arise in different frames. To give an example, we discuss the gravitational spectral shift as viewed in a general Weyl frame. We further explore the analogy of general relativity with scalar-tensor theories and show how a known Brans-Dicke vacuum solution may appear as a solution of general relativity theory when reinterpreted in a particular Weyl frame. Finally, we show that the so-called WIST gravity theories are mathematically equivalent to Brans-Dicke theory when viewed in a particular frame.