Horndeski meets McVittie: A scalar field theory for accretion onto
  cosmological black holes
  We show that the generalized McVittie spacetime, which represents a black
hole with time-dependent mass in an expanding universe, is an exact solution of
a subclass of the Horndeski family of actions. The heat-flow term responsible
for the energy transfer between the black hole and the cosmological background
is generated by the higher-order kinetic gravity braiding term, which
generalizes the cuscuton action that yields McVittie with constant mass as a
solution. Finally, we show that this generalization can be understood in terms
of a duality realized by a disformal transformation, connecting the cuscuton
field theory to an extension of the Horndeski action which does not propagate
any scalar degrees of freedom. Our finding opens a novel window into studies of
non-trivial interactions between dark energy/modified gravity theories and
astrophysical black holes.
