Slowly rotating black hole in chiral scalar-tensor theory

TL;DR

This paper studies how a chiral scalar-tensor theory, which breaks parity symmetry, affects slowly rotating black holes, revealing that effects are quadratic in spin and cubic in coupling, with potential significance in strong gravity regimes.

Contribution

It extends known solutions in Chern-Simons gravity to include slowly rotating black holes within chiral scalar-tensor theory, highlighting parity violation effects at higher orders.

Findings

Parity violation effects are quadratic in spin and cubic in coupling.

Effects are suppressed in weak fields but may be significant in strong fields.

The solution's properties near the horizon and ergosphere are analyzed.

Abstract

The chiral scalar-tensor theory is an extension of the Chern-Simons modified gravity by introducing couplings between the first and second derivatives of the scalar field and parity-violating spacetime curvatures. A key feature of this theory is its explicit breaking of parity symmetry in the gravitational sector, which is expected to affect the spatial-time component of axisymmetric spacetime. In this paper, we investigate the effects of the chiral scalar-tensor theory on slowly rotating black holes by building on known solutions in the dynamical Chern-Simons modified gravity. Using perturbative methods with small coupling and slow rotation approximations, we find that the contributions of the chiral scalar-tensor theory appear at quadratic order in the spin and cubic order in the coupling constants. Furthermore, we explore the properties of this solution in the weak field and check its ergosphere and horizon. In the weak limit, we find that the effects of parity violation are suppressed in the weak field but could become significant in the strong field regime. These results provide insights into the behavior of parity-violating gravity in the presence of rotation and may be used for further investigations into its observational signatures.