Birkhoff's Theorem and Uniqueness: A Peek Beyond General Relativity
Abstract
In General Relativity, Birkhoff's theorem asserts that any spherically symmetric vacuum solution must be static and asymptotically flat. In this paper, we study the validity of Birkhoff's theorem for a broad class of modified gravity theories in four spacetime dimensions, including quadratic and higher-order gravity models. We demonstrate that the Schwarzschild spacetime remains the unique Einstein branch solution outside any spherically symmetric configuration of these theories. Consequently, unlike black holes, the breakdown of junction conditions at the surface of the star further implies that the actual spacetime metric outside a horizonless star in these modified theories cannot simultaneously be spherically symmetric and remain within the Einstein branch. This insight offers a unique observational probe for theories beyond General Relativity.
Keywords
Cite
@article{arxiv.2411.09193,
title = {Birkhoff's Theorem and Uniqueness: A Peek Beyond General Relativity},
author = {Rajes Ghosh and Akash K Mishra and Avijit Chowdhury},
journal= {arXiv preprint arXiv:2411.09193},
year = {2025}
}
Comments
Accepted in Physics Letters B: 8 pages, no figure