Primordial Gravitational Waves in Bimetric Gravity

TL;DR

This paper investigates the generation and evolution of primordial gravitational waves during inflation within a minimal bimetric gravity model, revealing suppression effects and decay behaviors of tensor modes.

Contribution

It provides the first detailed calculation of tensor perturbations in bimetric gravity during inflation, highlighting the decay of massive modes and suppression of the power-spectrum.

Findings

Massless tensor mode power-spectrum remains constant during inflation.

Massive tensor mode and cross spectra decay rapidly during inflation.

Physical power-spectrum amplitude is suppressed due to flavor mixing.

Abstract

We study primordial tensor power-spectra generated during inflation in bimetric gravity. More precisely, we examine a homogeneous expanding spacetime in a minimal bimetric model with an inflaton and calculate tensor perturbations on the homogeneous background under slow-roll approximation. In terms of the mass eigenstates, only the power-spectrum of the massless state remains constant and both the power-spectrum of the massive state and the cross power-spectrum rapidly decay during inflation. The amplitude of the physical power-spectrum is suppressed due to the flavor mixing. All power-spectra in the flavor eigenstates coincide with each other up to the first order of the slow-roll parameter.