Alignment of Yukawa couplings in two Higgs doublet models

Abstract: We study the alignment of Yukawa couplings in the framework of general two Higgs doublet models (2HDMs) considering a scenario in which the lightest neutral Higgs boson is purely CP even while the two heavier neutral Higgs bosons are allowed to mix in the presence of nontrivial CP-violating phases in the Higgs potential. Identifying the lightest neutral Higgs boson as the 125 GeV one discovered at the LHC, we find that the alignment of Yukawa couplings without decoupling could be easily achieved in the type-I 2HDM with no much conflict with the current LHC Higgs precision data. Otherwise, we observe that the Yukawa couplings of the lightest Higgs boson could decouple much slowly compared to the Higgs coupling to a pair of massive vector bosons and they significantly deviate from the corresponding SM values even when the deviation of the Higgs to vector boson coupling is below the percent level. On the other hand, independently of 2HDM type and regardless of decoupling, we find a wrong-sign alignment limit of the Yukawa couplings in which the Yukawa couplings to the down-type quarks and/or those to the charged leptons are equal in strength but opposite in sign to the corresponding SM ones. The magnitude and sign of the up-type quark Yukawa couplings remain the same as in the SM. Accordingly, in this limit, all four types of 2HDMs are viable against the LHC Higgs precision data.