Confronting the fourth generation two Higgs doublet model with the phenomenology of heavy Higgs bosons

Abstract

A sequential fourth generation is known to be excluded because the non-decoupling contribution to ${\kappa }_g$, the Higgs coupling modifier with a gluon pair, is unacceptably large. Recently a new way to save the model was suggested in the Type-II two Higgs doublet model: if the Yukawa couplings of down-type fermions have wrong-sign, the contributions from $t^{\prime }$ and $b^{\prime }$ to ${\kappa }_g$ are cancelled. We study the theoretical and experimental constraints on this model, focusing on the heavy Higgs bosons. Two constraining features are pointed out. First the exact wrong-sign limit does not allow the alignment, which makes the perturbative unitarity for the scalar-scalar scattering put the upper bounds on the heavy Higgs boson masses like $M_H,M_A\lesssim 920$ GeV and $M_{H^{\pm }}\lesssim 620$ GeV. Secondly, the Yukawa couplings of the fourth generation fermions to the heavy Higgs bosons are generically large as being proportional to the heavy fermion mass and, for the down-type fermions, to $\tan \beta$ as well. The gluon fusion productions of $H$ and $A$ through the fourth generation quark loops become significant. We found that the current LHC data on $pp\to ZZ$ for $H$ along with the theoretical and indirect constraints exclude the model at leading order.

Comments: 30 pages with 17 figures