Theory and phenomenology of a four dimensional string-corrected black hole

TL;DR

This paper constructs a four-dimensional string-corrected black hole model, explores its theoretical properties such as entropy and singularity structure, and assesses its observational distinguishability from Schwarzschild black holes.

Contribution

It introduces a novel 4D string-corrected black hole model and analyzes its theoretical features and observational signatures, connecting string theory corrections with astrophysical phenomena.

Findings

String corrections match generalized uncertainty principle effects.

Black hole entropy gains logarithmic corrections.

Observational differences from Schwarzschild black holes are too small to detect with current data.

Abstract

We construct an effective four dimensional string-corrected black hole (4D SCBH) by rescaling the string coupling parameter in a $D$-dimensional Callan-Myers-Perry black hole. From the theoretical point of view, the most interesting findings are that the string corrections coincide with the so-called generalized uncertainty principle (GUP) corrections to black hole solutions, Bekenstein-Hawking entropy acquires logarithmic corrections, and that there exists a critical value of the coupling parameter for which the black hole temperature vanishes. We also find that, due to the string corrections the nature of the central singularity may be altered from spacelike to timelike singularity. In addition, we study the possibility of testing such a black hole with astrophysical observations. Since the dilaton field does not decouple from the metric it is not a priori clear that the resulting 4D SCBH offers only small corrections to the Schwarzschild black hole. We used motion of the S2 star around the black hole at the center of our galaxy to constrain the parameters (the string coupling parameter and ADM mass) of the 4D SCBH. To test the weak gravity regime we calculate the deflection angle in this geometry and apply it to gravitational lensing. To test the strong field regime, we calculate the black hole shadow radius. While we find that the observables change as we change the string coupling parameter, the magnitude of the change is too small to distinguish it from the Schwarzschild black hole. With the current precision, to the leading order terms, the 4D SCBH cannot be distinguished from the Schwarzschild black hole.