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.
Highlights
Even if the Standard Model (SM) is the favorite candidate to explain all the results obtained at the Large Hadron Collider (LHC), models with extended symmetries beyond the SM are of great interest due to their elegant UV completion along with the power of stabilizing the scalars against radiative corrections—i.e., solving the gauge hierarchy problem [1]
From the flavor data and Zbb, we find that the charged Higgs mass is relaxed, with tan β being restricted to 0.5–5, whereas the charged Higgs mass is pushed to larger than 1 TeV along with tan β being further restricted to < 3 when the LHC bounds are incorporated
Scenarios, the extended scalar sector manifests from the Goldstone bosons, and unbroken symmetry does contain the SM electroweak group SUð2Þ × Uð1Þ. These sets of models, where the Higgs boson emerges as a “little” part of a bigger representation and where some global symmetry is broken by the interplay between two or more coupling constants, are termed little Higgs (LH) models [3], and many different variations of these models have been proposed in literature [5,6,7,8]
Summary
Even if the Standard Model (SM) is the favorite candidate to explain all the results obtained at the Large Hadron Collider (LHC), models with extended symmetries beyond the SM are of great interest due to their elegant UV completion along with the power of stabilizing the scalars against radiative corrections—i.e., solving the gauge hierarchy problem [1]. Scenarios, the extended scalar sector manifests from the Goldstone bosons, and unbroken symmetry does contain the SM electroweak group SUð2Þ × Uð1Þ These sets of models, where the Higgs boson emerges as a “little” part of a bigger representation and where some global symmetry is broken by the interplay between two or more coupling constants, are termed little Higgs (LH) models [3], and many different variations of these models have been proposed in literature [5,6,7,8]. It is worthwhile to study how the neutral and the charged BSM scalars can modify the flavor and other EW observables, and impose constraints on the emergent 2HDM parameters derived from the LSS little Higgs model. For a detailed description of the model, we refer to Refs. [21,22]
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