Abstract
Cosmological perturbations of FRW solutions in ghost free massive bigravity, including also a second matter sector, are studied in detail. At early time, we find that sub horizon exponential instabilities are unavoidable and they lead to a premature departure from the perturbative regime of cosmological perturbations.
Highlights
Dark energy is the dominant component of our Universe; if future observations will establish that its equation of state differs from the one of a cosmological constant contribution, we have a case for modifying general relativity (GR) at large distances and massive gravity can be a compelling candidate
We studied in detail the dynamics of scalar perturbations in massive bigravity
The ghost free massive gravity theories can be classified according to the global symmetries of the potential V in the unitary gauge [18]
Summary
Dark energy is the dominant component of our Universe; if future observations will establish that its equation of state differs from the one of a cosmological constant contribution, we have a case for modifying general relativity (GR) at large distances and massive gravity can be a compelling candidate. Within the general class of theories that propagate 5 degrees of freedom (DoF) found in [17,18], in the Lorentz breaking case most of the theories have a much safer cutoff Λ2 1⁄4 ðmMPlÞ1=2 ≫ Λ3 and avoid all of the phenomenological difficulties mentioned above, including troubles with cosmology [19] Another option is to promote the nondynamical metric entering in the construction of massive gravity theory to a dynamical one [20,21] entering in the realm of bigravity originally introduced by Isham, Salam, and Strathdee [22].
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