The CST Bounce Universe model -- a parametric study

TL;DR

This paper explores the CST Bounce Universe model, a string theory-inspired cosmological scenario that avoids singularities and can produce sufficient inflation, offering an alternative to traditional inflationary models.

Contribution

It provides a detailed parameter space analysis of the CSTB model, demonstrating its viability to produce a single bounce and address key cosmological problems.

Findings

The CSTB model can produce a single bounce leading to a radiation-dominated universe.

It naturally generates enough e-foldings to solve flatness, horizon, and homogeneity problems.

The model is ghost-free and satisfies the null energy condition.

Abstract

A bounce universe model with a scale-invariant and stable spectrum of primordial density perturbations was constructed using a consistent truncation of the D-brane dynamics from Type IIB string theory. A coupling was introduced between the tachyon field and the adjoint Higgs field on the D3-branes to lock the tachyon at the top of its potential hill and to model the bounce process, which is known as the Coupled Scalar and Tachyon Bounce (CSTB) Universe. The CSTB model has been shown to be ghost free, and it fulfils the null energy condition; in addition, it can also solve the Big Bang cosmic singularity problem. In this paper we conduct an extensive follow-up study of the parameter space of the CSTB model. In particular we are interested in the parameter values that can produce a single bounce to arrive at a radiation-dominated universe. We further establish that the CSTB universe is a viable alternative to inflation, as it can naturally produce a sufficient number of e-foldings in the locked inflation epoch and in the post-bounce expansion to overcome the four fundamental limitations of the Big Bang cosmology, which are flatness, horizon, homogeneity and singularity, resulting in a universe of the current size.