Emergent Universe from an Unstable de Sitter Phase

TL;DR

This paper explores conditions under which the universe can emerge from a non-singular, unstable de Sitter phase, analyzing scalar field models and cosmological scenarios involving dark matter and dark energy, with implications for universe evolution.

Contribution

It demonstrates that only a measure-zero set of trajectories lead to universe emergence from static or de Sitter states, and analyzes various cosmological models' evolution from an unstable de Sitter phase.

Findings

Emergence from static or de Sitter states occurs for measure-zero trajectories.

Flat and open models generally evolve from an unstable de Sitter state at high energies.

Some closed models exhibit bouncing or cyclic behavior, aligning with observable universe features.

Abstract

In the Emergent scenario, the Universe should evolve from a non-singular state replacing the typical singularity of General Relativity, for any initial condition. For the scalar field model in [1] we show that only a set of measure zero of trajectories leads to emergence, either from a static state (an Einstein model), or from a de Sitter state. Assuming a scenario based on CDM interacting with a Dark Energy fluid, we show that in general flat and open models expand from a non-singular unstable de Sitter state at high energies; for some closed models this state is a transition phase with a bounce, other closed models are cyclic. A subset of these models are qualitatively in agreement with the observable Universe, accelerating at high energies, going through a matter-dominated decelerated era, then accelerating toward a de Sitter phase.