Accelerating Universe in a Big Bounce Model

TL;DR

This paper presents a big bounce cosmological model with a variable cosmological constant derived from higher dimensions, explaining universe acceleration and matching observational data.

Contribution

It introduces a novel big bounce model with a time-variable dark energy component derived from higher dimensions, providing an exact solution for universe evolution stages.

Findings

Universe transitions from contraction to expansion at the bounce.

Late-time acceleration driven by dark energy overtaking matter.

Dark energy approaches two-thirds of total energy density over time.

Abstract

Recent observations of Type Ia supernovae provide evidence for the acceleration of our universe, which leads to the possibility that the universe is entering an inflationary epoch. We simulate it under a ``big bounce'' model, which contains a time variable cosmological ``constant'' that is derived from a higher dimension and manifests itself in 4D spacetime as dark energy. By properly choosing the two arbitrary functions contained in the model, we obtain a simple exact solution in which the evolution of the universe is divided into several stages. Before the big bounce, the universe contracts from a $\Lambda $-dominated vacuum, and after the bounce, the universe expands. In the early time after the bounce, the expansion of the universe is decelerating. In the late time after the bounce, dark energy (i.e., the variable cosmological ``constant'') overtakes dark matter and baryons, and the expansion enters an accelerating stage. When time tends to infinity, the contribution of dark energy tends to two third of the total energy density of the universe, qualitatively in agreement with observations.