The nanohertz stochastic gravitational wave background from cosmic string loops and the abundant high redshift massive galaxies

TL;DR

This paper explores whether cosmic string loops can explain the nanohertz gravitational wave background detected by pulsar timing arrays and examines their impact on high-redshift galaxy abundance, highlighting challenges in unifying these observations.

Contribution

It demonstrates that cosmic string loops can account for the SGWB data but faces difficulties in simultaneously explaining high-redshift galaxy observations, suggesting the need for model extensions or separate origins.

Findings

Cosmic string loops can explain the nanohertz SGWB with specific tension and density parameters.

Challenges exist in reconciling SGWB explanations with high-redshift galaxy data.

Model extensions or different physical origins may be necessary.

Abstract

Recently, pulsar timing array (PTA) experiments have provided compelling evidence for the existence of the nanohertz stochastic gravitational wave background (SGWB). In this work, we demonstrated that cosmic string loops generated from cosmic global strings offer a viable explanation for the observed nanohertz SGWB data, requiring a cosmic string tension parameter of $\log(G\mu) \sim -12$ and a loop number density of $\log N \sim 4$. Additionally, we revisited the impact of cosmic string loops on the abundance of massive galaxies at high redshifts. However, our analysis revealed challenges in identifying a consistent parameter space that can concurrently explain both the SGWB data and observations from the James Webb Space Telescope. This indicates the necessity for either extending the existing model employed in this research or acknowledging distinct physical origins for these two phenomena.