Bosonic seesaw mechanism in a classically conformal extension of the Standard Model

TL;DR

This paper introduces a bosonic seesaw mechanism within a classically conformal $U(1)_{B-L}$ extended Standard Model featuring two Higgs doublets, explaining electroweak symmetry breaking through radiative symmetry breaking and a natural hierarchy of couplings.

Contribution

It proposes a novel bosonic seesaw mechanism in a conformal $U(1)_{B-L}$ model, demonstrating natural hierarchy reduction and consistent electroweak symmetry breaking.

Findings

The hierarchy among Higgs quartic couplings is reduced at high energies.

Electroweak symmetry breaking is achieved via the bosonic seesaw mechanism.

Parameter regions satisfy perturbativity, stability, and naturalness constraints.

Abstract

We suggest the so-called bosonic seesaw mechanism in the context of a classically conformal $U(1)_{B-L}$ extension of the Standard Model with two Higgs doublet fields. The $U(1)_{B-L}$ symmetry is radiatively broken via the Coleman-Weinberg mechanism, which also generates the mass terms for the two Higgs doublets through quartic Higgs couplings. Their masses are all positive but, nevertheless, the electroweak symmetry breaking is realized by the bosonic seesaw mechanism. Analyzing the renormalization group evolutions for all model couplings, we find that a large hierarchy among the quartic Higgs couplings, which is crucial for the bosonic seesaw mechanism to work, is dramatically reduced toward high energies. Therefore, the bosonic seesaw is naturally realized with only a mild hierarchy, if some fundamental theory, which provides the origin of the classically conformal invariance, completes our model at some high energy, for example, the Planck scale. We identify the regions of model parameters which satisfy the perturbativity of the running couplings and the electroweak vacuum stability as well as the naturalness of the electroweak scale.