Cosmic Strings, Inflation, and Gravity Waves

TL;DR

This paper explores how Coleman-Weinberg inflation affects the gravitational wave background from cosmic strings, showing it can reconcile theoretical models with pulsar timing array observations and discussing monopole-string formation in grand unified theories.

Contribution

It demonstrates that Coleman-Weinberg inflation modifies the gravitational wave spectrum from cosmic strings, aligning theoretical predictions with observational bounds and data.

Findings

Inflation can suppress short string loop production.

Modified spectra are compatible with PPTA and NANOGrav data.

A realistic E6 model with monopoles and strings surviving inflation is presented.

Abstract

We investigate the impact of Coleman-Weinberg inflation on the stochastic gravity wave background spectrum emitted by intermediate scale cosmic strings. The string network is partially inflated and re-enters the horizon at later times after the end of inflation, such that the short string loops are not produced. This leads to a significant modification of the gravity wave spectrum that we explore in detail. We find that Coleman-Weinberg inflation can help to satisfy the Parkes Pulsar Timing Array (PPTA) bound for dimensionless string tension values in the range $G\mu > 1.1\times 10^{-10}$. We also identify the modified gravity wave spectra which, in the case of inflation, are compatible with the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) data. We then discuss the formation of monopoles and strings at the same breaking scale and the compatibility of the Monopole, Astrophysics and Cosmic Ray Observatory (MACRO) bound with the PPTA bound, and also with the NANOGrav data. Finally, an example of a realistic non-supersymmetric $E_6$ model incorporating successful Coleman-Weinberg inflation is presented in which monopoles and strings both survive inflation and are present at an observable level.