Stabilizing the Higgs potential with a Z$'$

TL;DR

This paper explores how introducing a Z' boson in U(1) extensions of the Standard Model can stabilize the electroweak vacuum by modifying the Higgs self-coupling and top quark Yukawa coupling, even without direct Higgs coupling.

Contribution

It identifies the conditions under which a Z' boson can stabilize the Higgs potential, including models where the Z' does not directly couple to the Higgs.

Findings

A Z' boson can stabilize the Higgs potential by increasing the Higgs self-coupling.

The Z' reduces the top quark Yukawa coupling, aiding stability.

Certain U(1) charge assignments lead to a stable electroweak vacuum.

Abstract

Current data point toward metastability of the electroweak vacuum within the Standard Model. We study the possibility of stabilizing the Higgs potential in U(1) extensions thereof. A generic Z$'$ boson improves stability of the scalar potential in two ways: it increases the Higgs self--coupling, due to a positive contribution to the beta--function of the latter, and it decreases the top quark Yukawa coupling, which again has a stabilizing effect. We determine the range of U(1) charges which leads to a stable electroweak vacuum. In certain classes of models, such stabilization is possible even if the Z$'$ does not couple to the Higgs and is due entirely to the reduction of the top Yukawa coupling. We also study the effect of the kinetic mixing between the extra U(1) and hypercharge gauge fields.