Variable Speed of Light Cosmology and Bimetric Gravity: An Alternative to Standard Inflation

TL;DR

This paper reviews a scalar-tensor bimetric gravity model with variable speed of light, proposing an alternative to inflation that predicts a nearly scale-invariant power spectrum and explores observational distinctions from standard inflation.

Contribution

It introduces a VSL bimetric gravity framework as an alternative to inflation, with specific predictions for the power spectrum and causal structure of early universe fluctuations.

Findings

Predicts a scale-invariant power spectrum with n_s=0.97

Fluctuation modes are causally connected via VSL mechanism

Cosmological constant is set to zero, independent of scalar potential

Abstract

A scalar-tensor bimetric gravity model of early universe cosmology is reviewed. The metric frame with a variable speed of light (VSL) and a constant speed of gravitational waves is used to describe a Friedmann-Robertson-Walker universe. The Friedmann equations are solved for a radiation dominated equation of state and the power spectrum is predicted to be scale invariant with a scalar mode spectral index $n_s=0.97$. The scalar modes are born in a ground state superhorizon and the fluctuation modes are causally connected by the VSL mechanism. The cosmological constant is equated to zero and there is no significant dependence on the scalar field potential energy. A possible way of distinguishing the metric gravity model from standard inflationary models is discussed.