Is flat rotation curve a sign of cosmic expansion?
  Four alternative proposals as the possible solutions for the rotation curve
problem are introduced on the basis of assumption that the cosmic expansion is
engaged with the galactic dynamics over the halo. The first one proposes a
modification of equivalence principle in an accelerating universe. The second
one proposes a modification of Mach principle in an expanding universe. The
third one proposes a dynamics of variable mass system for the halo in an
expanding universe, and the fourth one proposes the replacement of physical
radius with comoving one over the halo, in an expanding universe.
