Gravitational waves during inflation from a 5D large-scale repulsive gravity model

TL;DR

This paper explores how a 5D large-scale repulsive gravity model can generate a nearly scale-invariant spectrum of relic gravitational waves during inflation, connecting cosmological and astrophysical scales.

Contribution

It introduces a 5D Ricci-flat metric framework to derive tensor fluctuations, unifying cosmological and astrophysical gravitational wave predictions.

Findings

Spectrum is nearly scale invariant under certain conditions

Dynamical equations valid at both cosmological and astrophysical scales

Gravity-antigravity radius determines the scale transition

Abstract

We investigate, in the transverse traceless (TT) gauge, the generation of the relic background of gravitational waves, generated during an early inflationary stage, on the framework of a large-scale repulsive gravity model. We calculate the spectrum of the tensor metric fluctuations of an effective 4D Schwarzschild-de-Sitter metric, which is obtained after implementing a planar coordinate transformation on a 5D Ricci-flat metric solution, in the context of a non-compact Kaluza-Klein theory of gravity. We found that the spectrum is nearly scale invariant under certain conditions. One interesting aspect of this model is that is possible to derive dynamical field equations for the tensor metric fluctuations, valid not just at cosmological scales, but also at astrophysical scales, from the same theoretical model. The astrophysical and cosmological scales are determined by the gravity- antigravity radius, which is a natural length scale of the model, that indicates when gravity becomes repulsive in nature.