Spherically symmetric conformal gravity and "gravitational bubbles"

TL;DR

This paper explores spherically symmetric solutions in Weyl conformal gravity, revealing vacuum solutions including 'gravitational bubbles' that are compact, source-free, and impossible in General Relativity, with implications for universe creation.

Contribution

It provides a complete classification of vacuum solutions in spherical conformal gravity, introducing the concept of 'gravitational bubbles' and analyzing their properties and implications.

Findings

Discovery of vacuum solutions called 'gravitational bubbles' with zero Weyl tensor.

Classification of solutions with constant and varying curvature scalar.

Explicit forms of non-vacuum solutions like Vaidya and electrovacuum metrics.

Abstract

The general structure of the spherically symmetric solutions in the Weyl conformal gravity is described. The corresponding Bach equations are derived for the special type of metrics, which can be considered as the representative of the general class. The complete set of the pure vacuum solutions is found. It consists of two classes. The first one contains the solutions with constant two-dimensional curvature scalar of our specific metrics, and the representatives are the famous Robertson--Walker metrics. One of them we called the "gravitational bubbles", which is compact and with zero Weyl tensor. Thus, we obtained the pure vacuum curved space-times (without any material sources, including the cosmological constant) what is absolutely impossible in General Relativity. Such a phenomenon makes it easier to create the universe from "nothing". The second class consists of the solutions with varying curvature scalar. We found its representative as the one-parameter family. It appears that it can be conformally covered by the thee-parameter Mannheim--Kazanas solution. We also investigated the general structure of the energy-momentum tensor in the spherical conformal gravity and constructed the vectorial equation that reveals clearly some features of non-vacuum solutions. Two of them are explicitly written, namely, the metrics \`a la Vaidya, and the electrovacuum space-time metrics.