Eur. Phys. J. C (2020) 80: 1033
https://doi.org/10.1140/epjc/s10052-020-08612-5

Regular Article – Theoretical Physics

Equivalence of solutions between the four-dimensional novel and regularized EGB theories in a cylindrically symmetric spacetime

¹ Institute of Theoretical Physics and Research Center of Gravitation, Lanzhou University, 730000, Lanzhou, China
² School of Physical Science and Technology, Southwest University, 400715, Chongqing, China
³ Key Laboratory for Magnetism and Magnetic of the Ministry of Education, Lanzhou University, 730000, Lanzhou, China

^e liuyx@lzu.edu.cn

Received: 19 June 2020
Accepted: 28 October 2020
Published online: 8 November 2020

Abstract

Recently, a novel four-dimensional Einstein–Gauss–Bonnet (EGB) theory was presented to bypass the Lovelock’s theorem and to give nontrivial effects on the four-dimensional local gravity. The main mechanism is to introduce a redefinition $\alpha \to \alpha /(D-4)$ and to take the limit $D\to 4$. However, this theory does not have standard four-dimensional field equations. Some regularization procedures are then proposed to address this problem (http://arxiv.org/abs/2003.11552, http://arxiv.org/abs/2003.12771, http://arxiv.org/abs/2004.08362, http://arxiv.org/abs/2004.09472, http://arxiv.org/abs/2004.10716). The resultant regularized four-dimensional EGB theory has the same on-shell action as the original theory. Thus it is expected that the novel four-dimensional EGB theory is equivalent to its regularized version. However, the equivalence of these two theories is symmetry-dependent. In this paper, we test the equivalence in a cylindrically symmetric spacetime. The well-defined field equations of the two theories are obtained, with which our follow-up analysis shows that they are equivalent in such spacetime. Cylindrical cosmic strings are then considered as specific examples of the metric. Three sets of solutions are obtained and the corresponding string mass densities are evaluated. The results reveal how the Gauss–Bonnet term in four dimensions contributes to the string geometry in the new theory.