Cosmic Perturbations Through the Cyclic Ages

TL;DR

This paper studies how cosmological perturbations evolve in cyclic universe models, showing that each cycle's structures originate from quantum fluctuations in the previous cycle and that the ekpyrotic phase effectively solves horizon and flatness problems without inflation.

Contribution

It demonstrates that the ekpyrotic phase alone can resolve key cosmological issues and that perturbations are generated and evolve independently across cycles in the cyclic model.

Findings

Galaxies in one cycle originate from quantum fluctuations in the previous cycle.

The ekpyrotic phase ensures homogeneity, isotropy, and flatness within each horizon.

Global structure is complex due to superhorizon perturbations, not describable by simple FRW models.

Abstract

We analyze the evolution of cosmological perturbations in the cyclic model, paying particular attention to their behavior and interplay over multiple cycles. Our key results are: (1) galaxies and large scale structure present in one cycle are generated by the quantum fluctuations in the preceding cycle without interference from perturbations or structure generated in earlier cycles and without interfering with structure generated in later cycles; (2) the ekpyrotic phase, an epoch of gentle contraction with equation of state $w\gg 1$ preceding the hot big bang, makes the universe homogeneous, isotropic and flat within any given observer's horizon; and, (3) although the universe is uniform within each observer's horizon, the global structure of the cyclic universe is more complex, owing to the effects of superhorizon length perturbations, and cannot be described in a uniform Friedmann-Robertson-Walker picture. In particular, we show that the ekpyrotic phase is so effective in smoothing, flattening and isotropizing the universe within the horizon that this phase alone suffices to solve the horizon and flatness problems even without an extended period of dark energy domination (a kind of low energy inflation). Instead, the cyclic model rests on a genuinely novel, non-inflationary mechanism (ekpyrotic contraction) for resolving the classic cosmological conundrums.