Smoking-gun signatures of bounce cosmology from echoes of relic gravitational waves

TL;DR

This paper predicts a unique oscillatory pattern in relic gravitational waves spectrum caused by bounce cosmology, which can be tested with current and future gravitational wave detectors, offering a new way to explore early universe physics.

Contribution

It introduces a distinctive oscillatory feature in relic GWs spectrum as a signature of non-singular bounce cosmology, which is potentially observable with existing GW detectors.

Findings

Relic GWs spectrum shows oscillatory patterns at high frequencies.

The amplitude of the GWs spectrum is within the sensitivity of current detectors.

Oscillatory features are distinctive to bounce cosmology, differentiating it from inflationary models.

Abstract

We report a novel feature of relic gravitational waves (GWs) in non-singular bounce cosmologies that is testable in light of GWs astronomy. In non-singular bounce cosmologies, the effective potential $M_p^2 a^{\prime \prime}/a$ that governs the evolution of primordial GWs contains two peaks due to the existence of contraction phase prior to the standard expansion phase. Accordingly, relic GWs interference between the two peaks, resulting in a distinctive oscillatory feature in the spectrum, analog to the resonant tunneling effect in quantum mechanics. As a result, the GWs spectrum exhibits an oscillatory patterns on high frequecy regime, distinctive to other cosmological scenarios such as inflation. We show that the amplitude of GWs spectrum is high enough to reach the sensitivity of current and forthcoming GWs instruments, making our predictions falsifiable. Hence, our finding offers a promising way to experimentally test the non-singular bounce scenarios and search for new physics in early universe cosmologies.