2018/10/11 by Sin Kyu Kang, Zhuoni Qian, Jeonghyeon Song +1
Physics and Astronomy · #Black Holes and Theoretical Physics #Boson #Fermion #Higgs boson #Higgs field #Higgs mechanism #Particle physics #Particle physics theoretical and experimental studies #Physics #Quantum Chromodynamics and Particle Interactions #Scalar (mathematics) #Two-Higgs-doublet model #Unitarity #Yukawa potential #hep-ph
paper · pdf · doi:10.1103/physrevd.98.095025
published as Phys. Rev. D 98, 095025 (2018) · 30 pages with 17 figures
arxiv created 2018/10/11 · openalex publication_date 2018/11/27 · arxiv updated 2018/12/05 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
A sequential fourth generation is known to be excluded because the nondecoupling contribution to \ensuremathκg, 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^\ensuremath' and b^\ensuremath' to \ensuremathκg 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\ensuremath\lesssim920 GeV and M_H^\ifmmode±\else\textpm\fi\ensuremath\lesssim620 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\ensuremathβ 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\ensuremath→ZZ for H, along with the theoretical and indirect constraints, exclude the model at leading order.