Status and Prospects of the Two-Higgs-Doublet SU(6)/Sp(6) little-Higgs Model and the Alignment Limit

Abstract

We study in detail the little-Higgs model proposed by Low, Skiba and Smith with an SU(6)/Sp(6) group structure. The effective theory at the TeV scale is a two-Higgs doublet model (2HDM) with additional heavy vector-like fermions and vector-bosons. We identify a set of independent input parameters and develop expressions for masses and couplings in terms of these. We perform a random scan of the parameter space and find points that satisfy constraints, including the recent 8 TeV LHC Higgs measurements, namely, the Higgs mass, Higgs couplings to the top, bottom, $\tau$, $W^{\pm }$ and $Z$, top-quark mass, and collider bounds on colored vector-like fermions ($t^{\prime }$ and $b^{\prime }$), and also precision electroweak constraints. The LHC constraints on the $hWW$ and $hZZ$ couplings are satisfied by being close to the "alignment limit". We find how fine-tuned the model is after including these constraints. For the points that satisfy the constraints, we present the 1-loop effective couplings of the CP-even and CP-odd neutral scalars to two gluons including contributions of standard model and heavy vector-like quarks. We also present the branching ratios of the heavy neutral scalars into the $\gamma \gamma ,\tau \bar{\tau },b\bar{b},t\bar{t},WW,ZZ,Zh,hh$ modes, and the heavy charged scalar into $tb,\tau \nu ,cs,Wh$ modes. These will aid searches of the heavy scalars at the LHC and other future colliders.

Comments: 21 pages, 11 figures, Comments added