A Simple Model of two Little Higgses

TL;DR

This paper presents a simple little Higgs model based on the SU(9)/SU(8) coset with embedded $SU(3)\times U(1)$ electroweak gauge symmetry, yielding a two-Higgs-doublet sector at the electroweak scale. By arranging spurions and Yukawa couplings, it achieves one-loop quadratic-divergence cancellation while introducing a tower of TeV-scale heavy states. Precision electroweak data constrain the symmetry-breaking scale to $f \gtrsim 3.3$ TeV, corresponding to heavy gauge-boson masses around 1.5–1.8 TeV; the heavy fermion partner mass is more weakly constrained. The framework offers a simple, potentially UV-completable alternative to other little-Higgs constructions and predicts testable TeV-scale particles.

Abstract

We construct a little Higgs model using a simple global symmetry group SU(9) spontaneously broken to SU(8). The electroweak interactions are extended to SU(3)xU(1) and embedded in SU(9). At the electroweak scale, our model is a two Higgs-doublet model. At the TeV scale, there are additional states, which are responsible for the cancellation of one loop quadratic divergences. We compute the effects of heavy states on the precision electroweak observables and find that the lower bounds on the masses of heavy gauge bosons and fermions are between 1 and 2 TeV.

Figures (2)

• Figure 1: 95% confidence level bound on $f$ as a function of the mixing parameter $\eta$.
• Figure 2: Mass of the heavy fermion $\chi$ in the parameter space $f_2/f_1$ versus $\lambda_1$, for large $\tan \beta$ on the left and $\tan \beta = 1$ on the right.