Extreme Compactness, Extreme Gravity: Higher-Derivative Corrections to ECOs

TL;DR

This paper investigates how higher-derivative gravity theories, specifically Gauss-Bonnet and Einstein-dilaton-Gauss-Bonnet models, modify the compactness scale of extremely compact objects, with potential observational implications.

Contribution

It derives the compactness scale in higher-curvature gravity models and quantifies deviations from standard ECOs due to these corrections.

Findings

Higher-curvature corrections alter ECO compactness scales.

Corrections are proportional to the coupling constant and inverse powers of the horizon radius.

Potential observational effects in astrophysical systems are identified.

Abstract

Higher-derivative gravity theories offer insights into the behavior of extremely compact objects (ECOs). Focusing on Gauss-Bonnet (GB) and Einstein-dilaton-Gauss-Bonnet (EdGB) gravity, we derive the compactness scale in these models and demonstrate how higher-curvature corrections lead to deviations from the standard ECO compactness scale. The corrections are of order $\alpha/r_0^2$ in EGB gravity and $\alpha^2/r_0^4$ in EdGB gravity, where $\alpha$ is the coupling constant and $r_0$ is the horizon radius corresponding to the mass of the ECO. Observational constraints suggest these effects could be significant in certain astrophysical systems, providing a new perspective on the nature of extremely compact objects in models of modified gravity.