Emergent 2HDM in LSS Little-Higgs: Musings from Flavor and Electroweak Physics

TL;DR

This paper investigates the emergent two-Higgs doublet model within the Little-Higgs framework, analyzing its flavor physics, electroweak constraints, and LHC search bounds to understand its viability and parameter space restrictions.

Contribution

It provides a comprehensive analysis of the LSS Little-Higgs model's emergent 2HDM, highlighting its distinct constraints from flavor physics and collider searches compared to general 2HDMs.

Findings

The emergent 2HDM is less constrained by flavor and Zbb measurements.

Electroweak searches at the LHC impose severe bounds on the model.

Charged Higgs mass and tanβ are tightly constrained by combined data.

Abstract

The low energy effective theory ($\sim$ TeV) of the little-Higgs model with $SU(6)/Sp(6)$, as proposed by Low, Skiba and Smith (LSS), exhibits a two-Higgs doublet model (2HDM) structure. The symmetry dictates interesting Yukawa patterns, translating to non-trivial fermion couplings with both of the Higgs doublets. The couplings of the scalars with the fermions can induce flavor changing neutral currents (FCNC), which get constraints from flavor physics observables such as BR$(B\rightarrow X_s\gamma)$, $B_s - \bar{B}_s$ mixing etc. The precision measurement of $Z b \bar{b}$ vertex, the top and Higgs mass along with other Higgs coupling measurements at the Large Hadron Collider (LHC) also enforce severe restrictions on the LSS model. Direct LHC search results of beyond the Standard Model (BSM) particles also impose bounds on the masses. We probe the LSS model in view of the above constraints through a random scan in the multi-dimensional parameter space. We observe, on contrary to the general 2HDM scenario, the emergent 2HDM from the LSS model is less constrained from the flavor data and the $Z b \bar{b}$ measurement but is severely constrained form the electroweak (EW) searches at the LHC. From the flavor data and $Z b \bar{b}$, we find that the charged Higgs mass is relaxed with $\tan\beta$ being restricted to $0.5-5$, whereas the charged Higgs mass is pushed to larger than 1 TeV along with $\tan\beta$ being further restricted to $< 3$ when the LHC bounds are incorporated.