Stable cosmology in chameleon bigravity
  The recently proposed chameleonic extension of bigravity theory, by including
a scalar field dependence in the graviton potential, avoids several
fine-tunings found to be necessary in usual massive bigravity. In particular it
ensures that the Higuchi bound is satisfied at all scales, that no Vainshtein
mechanism is needed to satisfy solar-system experiments, and that the strong
coupling scale is always above the scale of cosmological interest all the way
up to the early universe. This paper extends the previous work by presenting a
stable example of cosmology in the chameleon bigravity model. We find a set of
initial conditions and parameters such that the derived stability conditions on
general flat Friedmann background are satisfied at all times. The evolution
goes through radiation dominated, matter dominated, and de Sitter eras. We
argue that the parameter space allowing for such a stable evolution may be
large enough to encompass an observationally viable evolution. We also argue
that our model satisfies all known constraints due to gravitational wave
observations so far and thus can be considered as a unique testing ground of
gravitational wave phenomenologies in bimetric theories of gravity.
