Axion induced angular momentum reversal in Kerr-like black holes

Understand

We consider a pseudoscalar axion-like field coupled to a Chern-Simons gravitational anomaly term.

• The axion field backreacts on a rotating Kerr black hole background, resulting in modifications in the spacetime.
• In an attempt to determine potentially observable signatures, we study the angular momentum of the system of the modified Kerr-like black hole and the axionic matter outside the horizon of the black hole.
• As the strength of the coupling of the axion field to the Chern-Simons term is increasing, the requirement that the total angular momentum of the system remain constant forces the black hole angular momentum to decrease.