Primordial fluctuations from inflation in dRGT bimetric theory of gravity

TL;DR

This paper studies primordial gravitational waves and curvature perturbations within dRGT bimetric gravity, revealing modifications to the tensor-to-scalar ratio and gravitational wave spectrum compared to general relativity.

Contribution

It demonstrates how dRGT bimetric gravity affects inflationary perturbations, including the tensor-to-scalar ratio and gravitational wave spectrum, using a simplified Einstein-like action.

Findings

Tensor-to-scalar ratio is larger than in GR for large field inflation.

The usual consistency relation for inflation holds.

Gravitational wave spectrum is steeper than in standard models.

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.