Processing of Cosmological Perturbations in a Cyclic Cosmology

TL;DR

This paper investigates how cosmological fluctuations evolve in cyclic universes, revealing that each cycle reddens the spectrum and that linear theory breaks down, challenging the notion of a truly cyclic universe.

Contribution

It demonstrates the spectral evolution of perturbations in cyclic cosmology and highlights the limitations of linear theory in such models.

Findings

Each cycle causes spectral reddening.

Linear theory breaks down due to amplitude increase.

A truly cyclic universe is unlikely when perturbations are included.

Abstract

The evolution of the spectrum of cosmological fluctuations from one cycle to the next is studied. It is pointed out that each cycle leads to a reddening of the spectrum. This opens up new ways to generate a scale-invariant spectrum of curvature perturbations. The large increase in the amplitude of the fluctuations quickly leads to a breakdown of the linear theory. More generaly, we see that, after including linearized cosmological perturbations, a cyclic universe cannot be truly cyclic.