Shadow Fermions, Messenger Scalars and Leptogenesis

TL;DR

This paper proposes a leptogenesis mechanism at the electroweak scale within a dark energy and dark matter model involving shadow fermions and messenger scalars, generating lepton asymmetry through their CP-violating decays.

Contribution

It introduces a novel leptogenesis scenario using shadow fermions and messenger scalars in an SU(2)Z gauge framework, linking dark matter and dark energy to baryogenesis.

Findings

Calculated lepton asymmetry from decay interference

Identified conditions for shadow fermion decay channels

Proposed shadow fermions as lepton asymmetry progenitors

Abstract

A mechanism for leptogenesis at the electroweak scale was investigated in a model of dark energy and dark matter proposed by one of us (PQH). This model involves an asymptotically free gauge group SU(2)Z and an axion-like particle with an SU(2)Z-instanton-induced potential which yields a scenario for the dark energy. Furthermore, the extended particle content of this SU(2)Z model contains a possible candidate for the cold dark matter, namely, the SU(2)Z "shadow" fermion, which couples with the Standard Model lepton through a scalar "messenger field" carrying both SU(2)Z and electroweak quantum numbers. Since these shadow fermions are in a real representation of SU(2)Z, lepton number can be violated in the Yukawa sector and a lepton number asymmetry can be generated in the SU(2)Z particle's decay which is also CP-violating and "out-of-equilibrium". The asymmetry coming from the interference between the tree-level and one-loop amplitudes was calculated for both messenger scalar and shadow fermion decays. It turns out, in order to have a non-vanishing lepton asymmetry and to be consistent with the unitarity condition, some shadow fermions have to decay into lighter messenger scalars, hence could be a candidate "progenitor" for the lepton asymmetry.