Bimetric Gravity, Variable Speed of Light Cosmology and Planck2013

TL;DR

This paper presents a bimetric gravity model with a variable speed of light that aligns with Planck 2013 data, solving key cosmological problems without inflation or multiverse assumptions.

Contribution

It introduces a novel bimetric gravity framework with variable light speed that matches observed CMB fluctuations and addresses horizon, flatness, and fine-tuning issues.

Findings

Scalar spectral index n_s ≈ 0.96

Running of spectral index α_s ≈ 8×10^{-4}

Model fits Planck 2013 CMB data

Abstract

A bimetric gravity model with a variable speed of light is shown to be in agreement with the results reported from the Planck satellite in 2013. The predicted scalar mode spectral index is $n_s\approx 0.96$ and its running is $\alpha_s\approx 8\times 10^{-4}$ when the fundamental length scale $\ell_0$ in the model is fixed to be $\ell_0\approx 10^5\ell_P$, where $\ell_P$ is the Planck length $\ell_P=1.62\times 10^{-33}\,{\rm cm}$, giving the observed CMB fluctuations: $\delta_H\approx 10^{-5}$. The enlarged lightcone ensures that horizon and flatness problems are solved. The model is free from many of the fine-tuning problems of the inflationary models and the fluctuations that form the seeds of structure formation do not lead to a chaotic inhomogeneous universe and the need for a multiverse.