Dark Energy and the Return of the Phoenix Universe

TL;DR

This paper explores cyclic universe models with dark energy, showing that a long dark energy phase enables the universe to survive through cycles despite perturbation challenges, leading to a universe structure different from eternal inflation.

Contribution

It demonstrates that a prolonged dark energy phase allows cyclic universe models to persist despite perturbation issues, offering a new perspective on universe stability and structure.

Findings

A long dark energy phase (around a trillion years) ensures cyclic universe survival.

Most of the universe fails to pass the ekpyrotic phase, but enough volume persists.

The universe's global structure differs from eternal inflation models.

Abstract

In cyclic universe models based on a single scalar field (e.g., the radion determining the distance between branes in M-theory), virtually the entire universe makes it through the ekpyrotic smoothing and flattening phase, bounces, and enters a new epoch of expansion and cooling. This stable evolution cannot occur, however, if scale-invariant curvature perturbations are produced by the entropic mechanism because it requires two scalar fields (e.g., the radion and the Calabi-Yau dilaton) evolving along an unstable classical trajectory. In fact, we show here that an overwhelming fraction of the universe fails to make it through the ekpyrotic phase; nevertheless, a sufficient volume survives and cycling continues forever provided the dark energy phase of the cycle lasts long enough, of order a trillion years. Two consequences are a new role for dark energy and a global structure of the universe radically different from that of eternal inflation.