Constraints on Pre-Big-Bang Cosmology from Advanced LIGO and Advanced Virgo's First Three Observing Runs

TL;DR

This study uses data from Advanced LIGO and Virgo's first three observing runs to search for a gravitational-wave background predicted by pre-big-bang cosmology, setting constraints on its parameters and testing early Universe models.

Contribution

The paper provides the first Bayesian analysis constraining pre-big-bang cosmology parameters using gravitational-wave data, with no detection but meaningful bounds.

Findings

No evidence for PBB-induced SGWB was found.

Established a lower bound on the model parameter $eta$ at 95% confidence.

Results are consistent with the theoretical framework of PBB cosmology.

Abstract

We search for the stochastic gravitational-wave background (SGWB) predicted by pre-big-bang (PBB) cosmology using data from the first three observing runs of Advanced LIGO and Advanced Virgo. PBB cosmology proposes an alternative to cosmic inflation where the Universe evolves from a weak-coupling, low-curvature state to the hot Big Bang through a high-curvature bounce phase, predicting a distinctive SGWB spectrum. We perform a Bayesian analysis of the cross-correlation data to constrain the model parameters characterizing the PBB spectrum. We find no evidence for a PBB-induced SGWB, with a Bayes factor of $0.03$ between the PBB and noise-only model, strongly favoring the noise-only hypothesis. Our analysis establishes a lower bound $\beta \gtrsim -0.19$ at $95\%$ confidence level, which is compatible with the theoretical requirement $\beta \geq 0$ for a smooth bounce transition. While we do not detect a signal, our constraints remain consistent with the basic theoretical framework of PBB cosmology, demonstrating the potential of gravitational-wave observations to test early Universe theories.