Inflationary perturbations in bimetric gravity
  In this paper we study the generation of primordial perturbations in a
cosmological setting of bigravity during inflation. We consider a model of
bigravity which can reproduce the $\Lambda$CDM background and large scale
structure and a simple model of inflation with a single scalar field and a
quadratic potential. Reheating is implemented with a toy-model in which the
energy density of the inflaton is entirely dissipated into radiation. We
present analytic and numerical results for the evolution of primordial
perturbations in this cosmological setting. We find that the amplitude of
tensor perturbations generated during inflation is sufficiently suppressed to
avoid the effects of the tensor instability discovered in Refs.[1,2] which
develops during the cosmological evolution in the physical sector. We argue
that from a pure analysis of the tensor perturbations this bigravity model is
compatible with present observations. However, we derive rather stringent
limits on inflation from the vector and scalar sectors.
