Signatures of Einstein-Maxwell dilaton-axion gravity from the observed jet power and the radiative efficiency

Blandford-Znajek Process in Quadratic Gravity

“…Previous studies of the BZ mechanism outside GR [23][24][25] have only been considered to first relative order in the small-spin expansion, where a degeneracy occurs that hinders our ability to use this mechanism to distinguish GR from other theories of gravity. Furthermore, [23,24] have used parametrically deformed metrics with only one deformation parameter.…”

“…However, most of the known modified solutions cannot be mapped to such metrics (with only one deformation parameter), and when multiple parameters are included in the analyses of observables, the degeneracies between the astrophysical and BH parameters are enhanced, making theory-agnostic studies very challenging [59,60]. Therefore studies of specific theories, as the one presented here or in [25], should be seen as complementary.…”

“…Recent studies of the BZ process in modified gravity theories (e.g. [23,25,41]) adopted this suggestion and gave estimates of the BZ power in the slow-rotation limit without solving for the fields. This treatment, however, is not justified since Ω ≈ Ω H /2 may not hold in general, i.e., for other theories of gravity.…”

“…In modified gravity, however, the BZ mechanism has been much less studied than in GR, and when considered, it has been studied only analytically. For instance, in [22][23][24][25], the BZ power was computed to leading order in the BH's spin, either for an agnostic, parametrically deformed ("bumpy" [26]) BH metric [22][23][24] or for a theory-specific (Kerr-Sen) BH metric [25].…”

Blandford-Znajek jets in MOdified Gravity

“…Recently there have been efforts to understand how deviations from GR can manifest in the physics of relativistic jets. Examples range from studies on emission mechanisms in regular black hole metrics [35], Kerr-Sen black holes [36], quadratic and cubic theories of gravity [37,38], and on signatures from extra dimensions [39]. A first attempt to investigate how MOG deformations reflect on jet dynamics has been conducted in [40], where the Blandford & Payne mechanism [41] was assumed to cause the jet launching and particle trajectories around Kerr-MOG black holes were computed.…”