CP Violation from Scatterings with Gauge Bosons in Leptogenesis

TL;DR

This paper calculates the CP asymmetry in scatterings involving heavy neutrinos and gauge bosons within the leptogenesis framework, revealing new contributions that differentiate these asymmetries from decay asymmetries.

Contribution

It provides the first explicit computation of CP asymmetry in scatterings with gauge bosons, including novel vertex and box diagram contributions.

Findings

CP asymmetry in gauge boson scatterings differs from decay asymmetry.

New one-loop vertex and box diagram contributions are identified.

CP asymmetry persists even with hierarchical right-handed neutrinos.

Abstract

We present an explicit computation of the CP asymmetry in scattering processes involving the heavy right-handed neutrinos of the type I seesaw framework and the Standard Model gauge bosons. Compared to CP violation in two--body decays and in scatterings with top quarks there are new contributions at one loop in the form of new type of vertex corrections as well as of box diagrams. We show that their presence implies that, unlike the CP asymmetry in scatterings with top quarks, the CP asymmetry in scatterings with gauge bosons is different from the two-body decay asymmetry even for hierarchical right-handed neutrinos. This also holds for the L-conserving CP asymmetry in scatterings with U(1)$_Y$ gauge bosons.