The Ekpyrotic Universe: Colliding Branes and the Origin of the Hot Big Bang

TL;DR

This paper introduces a cosmological model where the hot big bang results from brane collision in extra-dimensional space, addressing key cosmological problems without inflation and predicting a distinctive gravitational wave spectrum.

Contribution

It presents a novel brane collision scenario within heterotic M-theory that explains the universe's origin and structure without inflation.

Findings

Addresses horizon, flatness, and monopole problems

Predicts a strongly blue gravitational wave spectrum

Generates nearly scale-invariant density perturbations

Abstract

We propose a cosmological scenario in which the hot big bang universe is produced by the collision of a brane in the bulk space with a bounding orbifold plane, beginning from an otherwise cold, vacuous, static universe. The model addresses the cosmological horizon, flatness and monopole problems and generates a nearly scale-invariant spectrum of density perturbations without invoking superluminal expansion (inflation). The scenario relies, instead, on physical phenomena that arise naturally in theories based on extra dimensions and branes. As an example, we present our scenario predominantly within the context of heterotic M-theory. A prediction that distinguishes this scenario from standard inflationary cosmology is a strongly blue gravitational wave spectrum, which has consequences for microwave background polarization experiments and gravitational wave detectors.