125 GeV Higgs state in the context of four generations with two Higgs doublets

Abstract

We interpret the recent discovery of a 125 GeV Higgs-like state in the context of a two-Higgs-doublet model with a heavy fourth sequential generation of fermions, in which one Higgs doublet couples only to the fourth-generation fermions, while the second doublet couples to the lighter fermions of the first three families. This model is designed to accommodate the apparent heaviness of the fourth-generation fermions and to effectively address the low-energy phenomenology of a dynamical electroweak-symmetry-breaking scenario. The physical Higgs states of the model are, therefore, viewed as composites primarily of the fourth-generation fermions. We find that the lightest Higgs, $h$, is a good candidate for the recently discovered 125 GeV spin-zero particle, when $\mathrm{tan}\ensuremath{\beta}\ensuremath{\sim}\mathcal{O}(1)$, for typical fourth-generation fermion masses of ${M}_{4\mathrm{G}}=400--600\text{ }\text{ }\mathrm{GeV}$, and with a large $t\mathrm{\text{\ensuremath{-}}}{t}^{\ensuremath{'}}$ mixing in the right-handed quark sector. This, in turn, leads to $\mathrm{BR}({t}^{\ensuremath{'}}\ensuremath{\rightarrow}th)\ensuremath{\sim}\mathcal{O}(1)$, which drastically changes the ${t}^{\ensuremath{'}}$ decay pattern. We also find that, based on the current Higgs data, this two-Higgs-doublet model generically predicts an enhanced production rate (compared to the Standard Model) in the $pp\ensuremath{\rightarrow}h\ensuremath{\rightarrow}\ensuremath{\tau}\ensuremath{\tau}$ channel, and reduced rates in the $VV\ensuremath{\rightarrow}h\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\gamma}$ and $p\overline{p}/pp\ensuremath{\rightarrow}V\ensuremath{\rightarrow}hV\ensuremath{\rightarrow}Vbb$ channels. Finally, the heavier $CP$-even Higgs is excluded by the current data up to ${m}_{H}\ensuremath{\sim}500\text{ }\text{ }\mathrm{GeV}$, while the pseudoscalar state, $A$, can be as light as 130 GeV. These heavier Higgs states and the expected deviations from the Standard Model din some of the Higgs production channels can be further excluded or discovered with more data.