Electric Dipole Moments from Post-Sphaleron Baryogenesis

TL;DR

This paper proposes a low-scale baryogenesis model involving diquark scalars that violate baryon number and can explain the universe's matter-antimatter asymmetry, while analyzing constraints from electric dipole moment measurements.

Contribution

It introduces a novel low-scale baryogenesis mechanism with diquark scalars and examines phenomenological constraints from EDM measurements.

Findings

The model can generate the observed baryon asymmetry with couplings to left-handed quarks.

Electric dipole moments impose strong constraints, favoring couplings to left-handed quarks.

Constraints from neutron and mercury EDM measurements are critical for model viability.

Abstract

We consider a model in which baryogenesis occurs at low scale, at a temperature below the electroweak phase transition. This model involves new diquark-type scalars which carry baryon number. Baryon number violation is introduced in the scalar potential, permitting $\Delta B=2$ violating process involving Standard Model quarks while avoiding stringent proton decay constraints. Depending on their quantum number assignment, the diquark-type scalars can couple to either right or left handed quarks, or to both. We show that this model can provide a viable explanation of the baryon asymmetry of the universe provided that the coupling to left handed quarks are present. However, the coexistence of couplings to left and right handed quarks introduces important phenomenological constraints on the model, such as radiative contributions to quark masses and the generation of electric dipole moments for nuclei, which probe the CP even and CP odd products of the relevant couplings constants, respectively. We demonstrate that the strongest such constraints arise from electric dipole moment measurements of the neutron and $^{199}$Hg. These constraints are sufficiently strong that, in the absence of an intricate flavor structure, baryogenesis must be dominated by the couplings of the new scalars to left handed quarks.