Cosmic Strings

TL;DR

Cosmic strings are linear energy concentrations formed during early universe phase transitions, with recent renewed interest due to potential links to fundamental superstring theory and their possible macroscopic sizes.

Contribution

This paper reviews the formation, properties, and evolving significance of cosmic strings, highlighting their connection to fundamental strings in modern superstring and M-theory.

Findings

Cosmic strings are constrained to a sub-dominant role in structure formation.

Recent theories suggest possible macroscopic sizes of fundamental strings.

Cosmic strings may have observable effects on cosmic microwave background.

Abstract

Cosmic strings are linear concentrations of energy that form whenever phase transitions in the early universe break axial symmetries as originally shown by Kibble. They are the result of frustrated order in the quantum fields responsible for elementary particles and their interactions. For about two decades, motivation for their study was provided by the possibility that they could be behind the density inhomogeneities that led to the observed large-scale structures in the universe. Precision observations, particularly of the cosmic microwave background radiation, have limited strings to a sub-dominant role in structure formation. More recently, interest has been revived with the realization that there may be strong links between field theory cosmic strings and fundamental strings. The latter are the supposed ultimate building blocks of matter, and in their original context of superstring theory were thought to be microscopic. However, in its modern version---sometimes referred to as M-theory---it is possible and perhaps even mandatory to have macroscopic (cosmological-sized) fundamental strings...