Abstract
We investigate classically non-singular bounces caused by dark energy. In the presence of positive spatial curvature, vacuum energy, either in the form of a cosmological constant or a scalar field potential, allows for an open set of initial conditions leading to non-singular bounces, without any violation of the null energy condition. We study anisotropic Bianchi IX cosmologies, and demonstrate that they can even have multiple bounces, accompanied by intricate evolutions of the anisotropies that provide a non-singular analogue of mixmaster crunches. The relation of these solutions to more complete cosmological models, as well as to the recently proposed swampland criteria, are briefly discussed.
Highlights
Within the standard hot big bang model of cosmology, the idea of the big bang is firmly ingrained. This is mostly due to the singularity theorems of Penrose and Hawking [1], which show that under a wide range of conditions, and in the presence of matter that satisfies the null energy condition, general relativity implies that the current expansion phase must have been preceded by a curvature singularity
What is new in our paper is that we provide a systematic overview of explicit numerical solutions, thereby clearly illustrating the link with BKL/mixmaster crunches, and explaining some aspects of these solutions by making use of an analytic solution for axial Bianchi IX, while discussing the link with the recent swampland conjectures
Bounces occur due to established physics only, and without violations of the null energy condition
Summary
Within the standard hot big bang model of cosmology, the idea of the big bang is firmly ingrained. Importantly, they occur in the presence of known physics, without any exotic matter, without modifications to general relativity, and without the need for quantum theory.. II, we will first review the Bianchi IX spacetime, which is the most general homogeneous and anisotropic cosmology This allows us to exhibit nonsingular bounces in the presence of a cosmological constant, which constitutes the simplest example of dark energy. In this setting, we can immediately see the link with chaotic mixmaster behavior, which grows stronger at the edges of the allowed parameter space for bounces. What is new in our paper is that we provide a systematic overview of explicit numerical solutions, thereby clearly illustrating the link with BKL/mixmaster crunches, and explaining some aspects of these solutions by making use of an analytic solution for axial Bianchi IX, while discussing the link with the recent swampland conjectures
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