Leptogenesis and gravity: baryon asymmetry without decays

TL;DR

This paper introduces a novel gravitational mechanism for leptogenesis that generates the Universe's matter-antimatter asymmetry independently of particle decays, by leveraging curved-spacetime effects and Yukawa phases.

Contribution

It reveals that gravitational effects combined with CP-violating phases can produce baryon asymmetry without relying on heavy particle decays, expanding the understanding of leptogenesis.

Findings

Identified parameter regions where decays are unnecessary for asymmetry generation.

Demonstrated the full Boltzmann equation analysis of the asymmetry evolution.

Showed gravitational effects can solely account for the baryon asymmetry.

Abstract

A popular class of theories attributes the matter-antimatter asymmetry of the Universe to CP-violating decays of super-heavy BSM particles in the Early Universe. Recently, we discovered a new source of leptogenesis in these models, namely that the same Yukawa phases which provide the CP violation for decays, combined with curved-spacetime loop effects, lead to an entirely new gravitational mechanism for generating an asymmetry, driven by the expansion of the Universe and independent of the departure of the heavy particles from equilibrium. In this Letter, we build on previous work by analysing the full Boltzmann equation, exploring the full parameter space of the theory and studying the time-evolution of the asymmetry. Remarkably, we find regions of parameter space where decays play no part at all, and where the baryon asymmetry of the Universe is determined solely by gravitational effects.