Topological Defects from the Multiverse

TL;DR

This paper explores the formation and evolution of topological defects from the multiverse, estimating their distribution and potential detectability within our observable universe, especially considering collisions with our bubble in a multiverse scenario.

Contribution

It introduces the idea that topological defects can nucleate in the multiverse and studies their evolution, distribution, and potential observational signatures within our bubble universe.

Findings

Number of nearby defects is small even at high nucleation rates.

Simulated sky maps show the distribution of defect collisions.

Detection prospects improve with higher parent vacuum cosmological constant.

Abstract

Many theories of the early universe predict the existence of a multiverse where bubbles continuously nucleate giving rise to observers in their interior. In this paper, we point out that topological defects of several dimensionalities will also be produced in de Sitter like regions of the multiverse. In particular, defects could be spontaneously nucleated in our parent vacuum. We study the evolution of these defects as they collide with and propagate inside of our bubble. We estimate the present distribution of defects in the observable part of the universe. The expected number of such nearby defects turns out to be quite small, even for the highest nucleation rate. We also study collisions of strings and domain walls with our bubble in our past light cone. We obtain simulated full-sky maps of the loci of such collisions, and find their angular size distribution. Similarly to what happens in the case of bubble collisions, the prospect of detecting any collisions of our bubble with ambient defects is greatly enhanced in the case where the cosmological constant of our parent vacuum is much higher than the vacuum energy density during inflation in our bubble.