Signature of inflation in the stochastic gravitational wave background generated by cosmic string networks

TL;DR

This paper predicts a unique high-frequency gravitational wave signature from inflationary cosmic string networks, which, if observed, could confirm the inflationary origin of the early universe.

Contribution

It introduces a model to compute the gravitational wave spectrum from inflationary cosmic strings, revealing a distinctive high-frequency signature.

Findings

High-frequency signature in gravitational wave spectrum due to i-strings

A simple algorithm for spectrum computation from standard cosmic strings

Potential observational evidence for primordial inflation

Abstract

A cosmic string network created during an inflationary stage in the early Universe - here defined as i-string network - is expected to enter a transient stretching regime during inflation, in which its characteristic length is stretched to scales much larger than the Hubble radius, before attaining a standard evolution once the network re-enters the Hubble volume after inflation. During the stretching regime, the production of cosmic string loops and consequent emission of gravitational radiation are significantly suppressed. Here, we compute the power spectrum of the stochastic gravitational wave background generated by i-string networks using the velocity-dependent one scale model to describe the network dynamics, and demonstrate that this regime introduces a high-frequency signature on an otherwise standard spectrum of the stochastic gravitational wave background generated by cosmic strings. We argue that, if observed by current or forthcoming experiments, this signature would provide strong evidence for i-strings and, therefore, for (primordial) inflation. We also develop a simple single-parameter algorithm for the computation of the stochastic gravitational wave background generated by i-strings from that of a standard cosmic string network, which may be useful in the determination of the observational constraints to be obtained by current and forthcoming gravitational wave experiments.