Equilibrium configuration of perfect fluid orbiting around black holes
  in some classes of alternative gravity theories
  The hydrodynamic behaviour of perfect fluid orbiting around black holes in
spherically symmetric spacetime for various alternative gravity theories has
been investigated. For this purpose we have assumed an uniform distribution for
the angular momentum density of the rotating perfect fluid. The contours of
equipotential surfaces are illustrated in order to obtain the nature of inflow
and outflow of matters. It has been noticed that, the marginally stable
circular orbits originating from decreasing angular momentum density lead to
closed equipotential surfaces along with cusp allowing existence of accretion
disks. On the other hand, the growing part of angular momentum density exhibits
central rings for which stable configurations are possible. However inflow of
matter is prohibited. Among the solutions discussed in this work, the charged
$F(R)$ gravity and Einstein-Maxwell-Gauss-Bonnet solution exhibit inflow and
outflow of matter with central rings present. These varied accretion disk
structure of perfect fluid attribute these spacetimes astrophysical importance.
The effect of higher curvature terms predominantly arises from region near the
black hole horizon. Hence the structural difference of accretion disk in
modified gravity theories with comparison to general relativity may act as an
experimental probe for these alternative gravity theories.
