Leptogenesis from loop effects in curved spacetime

TL;DR

This paper introduces a novel gravitational leptogenesis mechanism driven by quantum loop effects in curved spacetime, which can generate matter-antimatter asymmetry during the early Universe's thermal equilibrium.

Contribution

It demonstrates how quantum loops in a CP-violating theory induce a curvature-dependent chemical potential for leptons, enabling leptogenesis in thermal equilibrium.

Findings

Explicit two-loop calculations show the asymmetry depends on sterile neutrino masses.

The mechanism can produce a lepton asymmetry sufficient to influence the baryon-to-photon ratio.

The process relies on the violation of the strong equivalence principle in curved spacetime.

Abstract

We describe a new mechanism - radiatively-induced gravitational leptogenesis - for generating the matter-antimatter asymmetry of the Universe. We show how quantum loop effects in C and CP violating theories cause matter and antimatter to propagate differently in the presence of gravity, and prove this is forbidden in flat space by CPT and translation symmetry. This generates a curvature-dependent chemical potential for leptons, allowing a matter-antimatter asymmetry to be generated in thermal equilibrium in the early Universe. The time-dependent dynamics necessary for leptogenesis is provided by the interaction of the virtual self-energy cloud of the leptons with the expanding curved spacetime background, which violates the strong equivalence principle and allows a distinction between matter and antimatter. We show here how this mechanism is realised in a particular BSM theory, the see-saw model, where the quantum loops involve the heavy sterile neutrinos responsible for light neutrino masses. We demonstrate by explicit computation of the relevant two-loop Feynman diagrams how these radiative corrections display the necessary dependence on the sterile neutrino masses to generate an asymmetry, and show how the induced lepton asymmetry may be sufficiently large to play an important role in determining the baryon-to-photon ratio of the Universe.