Constraints on the radio loud/radio quiet dichotomy from the fundamental
  plane
  The fundamental plane for black hole activity constitutes a tight correlation
between jet power, X-ray luminosity, and black hole mass. Under the assumption
that a Blandford-Znajek-type mechanism, which relies on black hole spin,
contributes non-negligibly to jet production, the sufficiently small scatter in
the fundamental plane shows that black hole spin differences of
$\mid$$\Delta$a$\mid \sim$1 are not typical among the active galactic nuclei
population. If $-$ as it seems $-$ radio loud and radio quiet objects are both
faithful to the fundamental plane, models of black hole accretion in which the
radio loud/radio quiet dichotomy is based on a spin dichotomy of
a$\sim$1/a$\sim$0, respectively, are difficult to reconcile with the
observations.
  We show how recent theoretical work based on differences in accretion flow
orientation between retrograde and prograde, accommodates a small scatter in
the fundamental plane for objects that do have non-negligible differences in
black hole spin values. We also show that the dichotomy in spin between the
most radio loud and the most radio quiet involves $\mid$$\Delta$a$\mid
\approx$0. And, finally, we show how the picture that produces compatibility
with the fundamental plane, also allows one to interpret other otherwise
puzzling observations of jets across the mass scale including 1) the recently
observed inverse relation between radio and X-rays at higher Eddington ratios
in both black hole X-ray binaries as well as active galactic nuclei and 2) the
apparent contradiction between jet power and black hole spin observed in X-ray
hard and transitory burst states in X-ray binaries.
