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 β≳−0.19 at 95% confidence level, which is compatible with the theoretical requirement β≥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.
@article{arxiv.2412.09461,
title = {Constraints on Pre-Big-Bang Cosmology from Advanced LIGO and Advanced Virgo's First Three Observing Runs},
author = {Qin Tan and Zu Cheng Chen and You Wu and Lang Liu},
journal= {arXiv preprint arXiv:2412.09461},
year = {2025}
}