Cosmological and High Energy Physics implications from gravitational-wave background searches in LIGO-Virgo-KAGRA's O1-O4a runs

TL;DR

This paper uses LIGO-Virgo-KAGRA gravitational-wave data from O1 to O4a runs to set constraints on early Universe processes, improving our understanding of fundamental physics and cosmology.

Contribution

It provides the first comprehensive analysis combining multiple runs to constrain a wide range of early Universe models through gravitational-wave background limits.

Findings

Set new upper limits on gravitational-wave background energy density.

Constrained parameters for phase transitions, cosmic strings, and other early Universe phenomena.

Demonstrated that current data significantly restricts various cosmological scenarios.

Abstract

We search for gravitational-wave background signals produced by various early Universe processes in the Advanced LIGO O4a dataset, combined with the data from the earlier O1, O2, and O3 (LIGO-Virgo) runs. The absence of detectable signals enables powerful constraints on fundamental physics. We derive gravitational-wave background energy density upper limits from the O1-O4a data to constrain parameters associated with various possible processes in the early Universe: first-order phase transitions, cosmic strings, domain walls, stiff equation of state, axion inflation, second-order scalar perturbations, primordial black hole binaries, and parity violation. In our analyses, the presence of an astrophysical background produced by compact (black hole and neutron star) binary coalescences throughout the Universe is also considered. We address the implications for various cosmological and high energy physics models based on the obtained parameter constraints. We conclude that LIGO-Virgo data already yield significant constraints on numerous early Universe scenarios.