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

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 vectorlike 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-+/- and Z, top-quark mass, and collider bounds on colored vector-like fermions (t' and b'), 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(tau) over bar, b (b) over bar, t (t) over bar, 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.