Semi-perturbative unification with extra vector-like families

TL;DR

This paper analyzes an extended supersymmetric model with vector-like families, showing how it achieves gauge coupling unification around 10^{16.9} GeV and explores conditions avoiding charge and color breaking minima.

Contribution

It provides a detailed two-loop analysis of gauge coupling unification and soft mass effects in an extended supersymmetric model with vector-like families, highlighting conditions for stability.

Findings

Gauge coupling unification at 10^{16.9} GeV with α_X ≈ 0.2.

Existence of parameter space avoiding charge and color breaking minima.

Upper bounds on the lightest Higgs boson mass from one-loop effective potential.

Abstract

We make a comprehensive analysis of an extended supersymmetric model(ESSM) obtained by adding a pair of vector-like families to the minimal supersymmetric standard model and having specific forms of 5 x 5 fermion mass matrices. The singlet Higgs couplings which link the ordinary to vector-like generations do not have the renormalization effects of the gauge interactions and hence the "quasi-infrared fixed point" near the scale of the top quark mass. The two-loop Yukawa effects on gauge couplings lead to an unified coupling $\alpha_X$ around 0.2 with an unification scale M_X of 10^{16.9} GeV. Large Yukawa effects in the high energy region arrest the growth of the QCD coupling near M_X making the evolution flat. The renormalization effects of the vector-like generations on soft mass parameters has important effects on the charge and color breaking(CCB)minima. We will show that there exists parameter space where there is no charge and color breaking. We will also demonstrate that there exists minima of the Higgs potential which satisfies the mass of the Z boson but avoid CCB. Upper limits on the mass of the lightest Higgs boson from the one-loop effective scalar potential is obtained for sets of universal soft supersymmetry breaking mass parameters.