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 nondecoupling contribution to ��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 the wrong sign, the contributions from t�� and b�� to ��g are canceled. We study the theoretical and experimental constraints on this model, focusing on the heavy Higgs bosons. We point out two constraining features. First, the exact wrong-sign limit does not allow alignment, which causes the perturbative unitarity for the scalar-scalar scattering to put upper bounds on the heavy Higgs boson masses like MH, MA 920 GeV and MH�� 620 GeV. Second, the Yukawa couplings of the fourth generation fermions to the heavy Higgs bosons are generically large, being proportional to the heavy fermion mass and, for the down-type fermions, to tan�� as well. The gluon fusion production of H and A through the fourth generation quark loops becomes significant. We find that the current LHC data on pp��ZZ for H, along with the theoretical and indirect constraints, exclude the model at leading order. (c) 2018 authors. Published by the American Physical Society