Testing Leptogenesis from Observable Gravitational Waves

Abstract

Leptogenesis provides an elegant mechanism to explain the observed baryon asymmetry of the Universe (BAU), yet its experimental verification remains challenging due to requirements of either extremely heavy right-handed neutrinos or precisely fine-tuned mass splittings. We adapt a solution by introducing an extra scalar field that significantly enhances $CP$ asymmetry through loop-level contributions. This scalar extension not only facilitates successful leptogenesis but also enables a strong first-order electroweak phase transition, generating potentially observable gravitational waves (GWs). We demonstrate a strong correlation between the generated BAU and the GW signal strength, establishing a unique way to test the leptogenesis. We show that when the model achieves a successful BAU, the resulting GW signal from EWPT can have signal-to-noise ratio of $\mathcal{O}(10^3)$ and $\mathcal{O}(10^6)$ at the upcoming LISA and DECIGO experiments, respectively. This work presents a concrete connection between successful leptogenesis and detectable GWs, offering a promising method for experimental testing of the leptogenesis mechanism through future GW observations.