Inflationary Theory versus Ekpyrotic/Cyclic Scenario

TL;DR

This paper reviews inflationary theory, critiques alternative models like ekpyrotic and cyclic scenarios, and proposes modifications to improve cyclic models by incorporating standard inflation, thereby addressing their major issues.

Contribution

It demonstrates that cyclic scenarios are not true alternatives to inflation and suggests adding a standard inflationary phase to resolve their problems.

Findings

Ekpyrotic scenario does not solve major cosmological problems.

Cyclic scenario is essentially a version of inflationary theory with unresolved issues.

Adding a standard inflation stage after the singularity simplifies and improves cyclic models.

Abstract

I will discuss the development of inflationary theory and its present status, as well as some recent attempts to suggest an alternative to inflation. In particular, I will argue that the ekpyrotic scenario in its original form does not solve any of the major cosmological problems. Meanwhile, the cyclic scenario is not an alternative to inflation but rather a complicated version of inflationary theory. This scenario does not solve the flatness and entropy problems, and it suffers from the singularity problem. We describe many other problems that need to be resolved in order to realize a cyclic regime in this scenario, produce density perturbations of a desirable magnitude, and preserve them after the singularity. We propose several modifications of this scenario and conclude that the best way to improve it is to add a usual stage of inflation after the singularity and use that inflationary stage to generate perturbations in the standard way. This modification significantly simplifies the cyclic scenario, eliminates all of its numerous problems, and makes it equivalent to the usual chaotic inflation scenario.