Pre-Big-Bang cosmology meets gravitational wave astronomy: constraints from advanced LIGO and advanced Virgo’s first three observing runs

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 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.