Physical effects of massless cosmic strings

TL;DR

This paper investigates the physical effects of massless cosmic strings, analyzing their influence on test body velocities and cosmic microwave background anisotropies, revealing different regimes based on the string's energy.

Contribution

It introduces a method to describe phenomena caused by massless cosmic strings considering parabolic holonomy, highlighting differences from massive strings at high energies.

Findings

Massless strings cause velocity perturbations and CMB anisotropies similar to massive strings at low energies.

At high energies, effects of massless strings significantly differ from those of massive strings.

The study provides a framework to analyze physical phenomena in spacetimes with massless strings.

Abstract

We study massless cosmic strings which are one-dimensional objects moving with the speed of light. Perturbations of velocities of test bodies and anisotropy of cosmic microwave background generated by massless cosmic strings are analysed. These phenomena are analogous to the string wake effect and the Kaiser-Stebbins effect for standard (massive) cosmic strings. There are two regimes depending on the energy $E$ of a massless string per unit length. At low energies, $EG/c^4\ll 1$, massless and massive strings act similarly. At high energies, $EG/c^4 \sim 1$, massless string effects are quite different. Our work provides a method to describe different physical phenomena on spacetimes of massless strings which take into account the presence of a parabolic holonomy.