On the efficiency of jet production in FR II radio galaxies and quasars
  Jet powers in many radio galaxies with extended radio structures appear to
exceed their associated accretion luminosities. In systems with very low
accretion rates, this is likely due to the very low accretion luminosities
resulting from radiatively inefficient accretion flows. In systems with high
accretion rates, the accretion flows are expected to be radiatively efficient,
and the production of such powerful jets may require an accretion scenario
which involves magnetically arrested discs (MADs). However, numerical
simulations of the MAD scenario indicate that jet production efficiency is
large only for geometrically thick accretion flows and scales roughly with
$(H/R)^2$, where $H$ is the disc height and $R$ is the distance from the BH.
Using samples of FRII radio galaxies and quasars accreting at moderate
accretion rates we show that their jets are much more powerful than predicted
by the MAD scenario. We discuss possible origins of this discrepancy,
suggesting that it can be related to approximations adopted in MHD simulations
to treat optically thick accretion flow within the MAD-zone, or may indicate
that accretion disks are geometrically thicker than the standard theory
predicts.
