FRW cosmology in Milgrom's bimetric theory of gravity
  We consider spatially homogeneous and isotropic Friedmann-Robertson-Walker
(FRW) solutions of Milgrom's recently proposed class of bimetric theories of
gravity. These theories have two different regimes, corresponding to high and
low acceleration. We find simple power-law matter dominated solutions in both,
as well as solutions with spatial curvature, and exponentially expanding
solutions. In the high acceleration limit these solutions behave like the FRW
solutions of General Relativity, with a cosmological constant term that is of
the correct order of magnitude to explain the observed accelerating expansion
of the Universe. We find that solutions that remain in the high acceleration
regime for their entire history, however, require non-baryonic dark matter
fields, or extra interaction terms in their gravitational Lagrangian, in order
to be observationally viable. The low acceleration regime also provides some
scope to account for this deficit, with solutions that differ considerably from
their general relativistic counterparts.
