Gravitational wave oscillations in bimetric cosmology

Understand

Unlike general relativity, in bimetric gravity linear gravitational waves do not evolve as free fields.

• In this theory there are two types of tensor perturbations, whose interactions are inherited from non-trivial couplings between two dynamical metric tensor fields in the Hassan-Rosen action, and are responsible for the phenomenon of bigravity oscillations.
• In this work, we analyze the dynamics of cosmological tensor modes in bimetric gravity on sub-horizon scales and close to the general relativity limit.
• In this limit, the system has a characteristic length scale $L$ that is strictly contained within the comoving Hubble radius.