Superradiance in modified gravity (MOG)

We consider the case of rotating black holes in a dark-matter-emulating theory of gravity called MOG. The latter introduces a gravitational vector field with an associated gravitational charge proportional to the black hole mass and a scalar field in place of the gravitational constant. The resulting black hole metrics resemble the Kerr-Newman geometry and enjoy superradiant scattering. MOG, however, presents important new features. By studying the scattering of a scalar field, we show that there is a marked reduction of the critical frequency of mode amplification. This corresponds to saying that the superradiance peak frequency is red shifted. Analyses of the reflected energy flux also show that MOG black holes are fainter with respect to the standard ones. The proposed results pave the way for testing MOG against astronomical observations.

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