A new mechanism for matter-antimatter asymmetry and connection with dark matter

TL;DR

This paper introduces a novel matter-antimatter asymmetry mechanism based on interference of tree-level diagrams involving unstable mediators, linking it to dark matter through a specific Standard Model extension.

Contribution

It presents a new CP-asymmetry generation mechanism using only tree-level diagrams and connects it to dark matter within a TeV-scale Standard Model extension.

Findings

CP asymmetry from tree-level interference demonstrated

Dark matter candidate identified in inert doublet

Baryon asymmetry and dark matter relic densities are related

Abstract

We propose a new mechanism for generating matter-antimatter asymmetry via the interference of tree-level diagrams only, where the imaginary part of the Breit-Wigner propagator for an unstable mediator plays a crucial role. We first derive a general result that a nonzero $CP$-asymmetry can be generated via at least two sets of interfering tree-level diagrams involving either $2\rightarrow2$ or $1\rightarrow n$ (with $n\geq3$) processes. We illustrate this point in a simple TeV-scale extension of the Standard Model with an inert Higgs doublet and right-handed neutrinos, along with an electroweak-triplet scalar field, where small Majorana neutrino masses are generated via a combination of radiative type-I and tree-level type-II seesaw mechanisms. The imaginary part needed for the required $CP$-asymmetry comes from the trilinear coupling of the inert doublet with the triplet scalar, along with the width of the triplet scalar mediator. The real part of the neutral component of the inert doublet serves as a cold dark matter candidate. The evolutions of the dark matter relic density and the baryon asymmetry are intimately related in this scenario.