Abstract
We investigate primordial gravitational waves and curvature perturbations in de Rham-Gabadadze-Tolley (dRGT) bimetric gravity. We evaluate the power-spectra in the leading order in slow roll. Taking into account the decay of massive graviton, we find that the action up to the second order reduces to the Einstein theory with a non-minimally coupled scalar field, which is simplified to a minimally coupled model by conformal transformation. We also find that the tensor to scalar ratio for large field inflation with power law potential is larger than the general relativity counterpart for any choice of parameters in dRGT bimetric gravity. In addition, we confirm that the usual consistency relation holds and we have a steeper spectrum for gravitational waves.
Highlights
In the slow roll limit, perturbations in the matter sector are decoupled from the gravitational sector, obey the equation of motion of a massless field and have a flat spectrum as in general relativity
Introducing an approximation, which is based on the decay of the massive gravitons and is valid at the leading order in slow roll, we calculated the spectrum of the tensor perturbation and that of the scalar perturbation generated during inflation
We found how the tensor to scalar ratio and the spectral index of the scalar perturbation are modified for general choice of model parameters in de Rham-Gabadadze-Tolley (dRGT) bimetric gravity except when the Higuchi bound is saturated
Summary
In the slow roll limit, perturbations in the matter sector are decoupled from the gravitational sector, obey the equation of motion of a massless field and have a flat spectrum as in general relativity. The massive scalar modes and the scalar field modes are coupled when we expand the perturbations with respect to the slow roll parameters.
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