On the No-Boundary Proposal for Ekpyrotic and Cyclic Cosmologies

TL;DR

This paper explores how the no-boundary proposal influences initial conditions in ekpyrotic and cyclic cosmologies, revealing that such conditions are more probable than inflationary scenarios and introducing new instanton solutions.

Contribution

It introduces the concept of ekpyrotic instantons within the no-boundary framework and compares their probabilities to inflationary initial conditions.

Findings

Ekpyrotic instantons can explain the universe's classicality.

In cyclic models, de Sitter-like instantons describe universe emergence.

Ekpyrotic and cyclic initial conditions are more probable than inflationary ones.

Abstract

The no-boundary proposal provides a compelling theory for the initial conditions of our universe. We study the implications of such initial conditions for ekpyrotic and cyclic cosmologies. These cosmologies allow for the existence of a new type of "ekpyrotic instanton", which describes the creation of a universe in the ekpyrotic contraction phase. Remarkably, we find that the ekpyrotic attractor can explain how the universe became classical. In a cyclic context, in addition to the ekpyrotic instantons there exist de Sitter-like instantons describing the emergence of the universe in the dark energy phase. Our results show that typically the ekpyrotic instantons yield a higher probability. In fact, in a potential energy landscape allowing both inflationary and cyclic cosmologies, the no-boundary proposal implies that the probability for ekpyrotic and cyclic initial conditions is vastly higher than that for inflationary ones.