Neutron Electric Dipole Moment in the Gauge-Higgs Unification

TL;DR

This paper investigates the neutron electric dipole moment within a five-dimensional gauge-Higgs unification model, highlighting spontaneous CP violation mechanisms and deriving bounds on the compactification scale based on one-loop calculations.

Contribution

It demonstrates how CP violation arises spontaneously in gauge-Higgs unification and calculates the neutron EDM at one-loop without three-generation assumptions.

Findings

Neutron EDM appears at one-loop level in the model.

Lower bound on compactification scale is approximately 2.6 TeV.

CP violation is linked to Higgs VEV and bulk mass terms.

Abstract

We study the neutron electric dipole moment (EDM) in a five dimensional SU(3) gauge-Higgs unification compactified on M^4 \times S^1/Z_2 space-time including a massive fermion. We point out that to realize the CP violation is a non-trivial task in the gauge-Higgs unification scenario and argue how the CP symmetry is broken spontaneously by the VEV of the Higgs, the extra space component of the gauge field. We emphasize the importance of the interplay between the VEV of the Higgs and the Z_2-odd bulk mass term to get physically the CP violation. We then calculate the one-loop contributions to the neutron EDM as the typical example of the CP violating observable and find that the EDM appears already at the one-loop level, without invoking to the three generation scheme. We then derive a lower bound for the compactification scale, which is around 2.6 TeV, by comparing the contribution due to the nonzero Kaluza-Klein modes with the experimental data.