Gravitating cosmic strings with flat directions

TL;DR

This paper investigates cosmic string models with flat directions in curved space-time, demonstrating that the zero mode persists when coupled to gravity and significantly influences local gravitational properties.

Contribution

It proves the survival of flat directions in string solutions when coupled to gravity and explores their impact on the local structure and gravitational effects.

Findings

Zero mode persists with gravity coupling

Flat direction affects local energy density

Parameter choice influences universe size in supermassive strings

Abstract

We study field theoretical models for cosmic strings with flat directions in curved space-time. More precisely, we consider minimal models with semilocal, axionic and tachyonic strings, respectively. In flat space-time, the string solutions of these models have a flat direction, i.e., a uniparametric family of configurations with the same energy exists which is associated to a zero mode. We prove that the zero mode survives coupling to gravity, and study the role of the flat direction when coupling the strings to gravity. Even though the total energy of the solution is the same, and thus the global properties of the family of solutions remains unchanged, the energy density, and therefore the gravitational properties, are different. The local structure of the solutions depends strongly on the value of the parameter describing the flat direction; for example, for supermassive strings, the value of the free parameter can determine the size of the universe.