Slow-rotating black holes with potential in dynamical Chern-Simons modified gravitational theory

TL;DR

This paper derives new slow-rotating black hole solutions in dynamical Chern-Simons gravity with a potential, showing how these solutions differ from Kerr and could pass weak-field experimental tests.

Contribution

It presents the first novel solutions for rotating black holes in dynamical Chern-Simons gravity with a potential, extending previous work by including non-zero potentials.

Findings

Solutions are axisymmetric and stationary with dipole scalar field distortion.

Metric corrections decay as inverse fourth power of radial distance when V∝φ.

Solutions potentially pass weak-field experimental constraints.

Abstract

The Chern-Simons amended gravity theory appears as a low-energy effective theory of string theory. The effective theory includes an anomaly-cancelation correction to the Einstein-Hilbert action. The Chern-Simons expression consists of the product $\varphi R \tilde R $ of the Pontryagin density $R \tilde R $ with a scalar field $\varphi$, where the latter is considered as a background field (dynamical construction or non-dynamical construction). Many different solutions to Einstein's general relativity continue to be valid in the amended theories. The Kerr metric is, however, considered an exceptional case that raised a search for rotating black hole solutions. We generalize the solution presented in Phys. Rev. D \textbf{77}, 064007 (2008) by allowing the potential $V$ to have a non-vanishing value and we discuss three different cases of the potential, that is, $V=\mathrm{const.}$, $V\propto \varphi$, and $V\propto \varphi^2$ cases. The present study presents, for the first time, novel solutions prescribing rotating black holes in the frame of the dynamical formulation of the Chern-Simons gravity, where we include a potential and generalize the previously derived solutions. We derive the solutions in the slow-rotation limit, where we write the parameter of the slow-rotation expansion by $\varepsilon$. These solutions are axisymmetric and stationary and they give a distortion of the Kerr solution by a dipole scalar field. Moreover, we investigate that the rectification to the metric behaves in the inverse of the fourth order of radial distance from the center of the black hole when $V\propto \varphi$. This suggests that any meaningful limits from the weak-field experiments could be passed.