Thin accretion disk signatures in dynamical Chern-Simons modified gravity

TL;DR

This paper investigates how dynamical Chern-Simons modified gravity affects accretion disk signatures around black holes, proposing observational tests to distinguish it from general relativity through electromagnetic spectra.

Contribution

It explores the observational signatures of dynamical CS modified gravity on accretion disks, including energy flux and emission spectra, providing a basis for testing the theory with astrophysical data.

Findings

Kerr black holes are more efficient energy converters than CS black holes.

Distinct electromagnetic signatures can differentiate CS gravity from general relativity.

Accretion disk properties in CS gravity show measurable deviations from Kerr solutions.

Abstract

A promising extension of general relativity is Chern-Simons (CS) modified gravity, in which the Einstein-Hilbert action is modified by adding a parity-violating CS term, which couples to gravity via a scalar field. In this work, we consider the interesting, yet relatively unexplored, dynamical formulation of CS modified gravity, where the CS coupling field is treated as a dynamical field, endowed with its own stress-energy tensor and evolution equation. We consider the possibility of observationally testing dynamical CS modified gravity by using the accretion disk properties around slowly-rotating black holes. The energy flux, temperature distribution, the emission spectrum as well as the energy conversion efficiency are obtained, and compared to the standard general relativistic Kerr solution. It is shown that the Kerr black hole provide a more efficient engine for the transformation of the energy of the accreting mass into radiation than their slowly-rotating counterparts in CS modified gravity. Specific signatures appear in the electromagnetic spectrum, thus leading to the possibility of directly testing CS modified gravity by using astrophysical observations of the emission spectra from accretion disks.