Fermion mass effects on Γ ( Z → bb̄ + a light Higgs ) in a two - Higgs - doublet model

Fermion mass effects on Γ(Z → b ¯ b + a light Higgs) in a two-Higgs-doublet model Abstract Large fermion mass effect on the Yukawa process Z → b ¯ b → b ¯ bh(A) in the entire range of the neutral Higgs boson masses is found. It is particularly important for light Higgs bosons, which are still not excluded experimentally in a general two-Higgs-doublet model. The light Higgs bosons in the context of the standard model (SM) and its minimal supersymmetric extension (MSSM) have been ruled out at LEP from zero up to a value that depends on the model assumed. In the framework of the SM the dominant Higgs boson production process is the Bjorken process and the mass limit m H SM ≥ 65.1 GeV has been established based on the results of 4 collaborations collecting data at LEP[1]. In extensions of the SM, like MSSM or general two-Higgs-doublet model (2HDM), the Higgs sector is much richer: there are two CP-even neutral Higgs bosons denoted by h and H (we assume that m h ≤ m H), a CP-odd neutral – A, and a pair of charged scalars H ±. The CP-even Higgs bosons can be produced via the process (1) however with lower rates because they share the couplings to Z boson, i.e. *) cos 2 (β − α) (3) where α and β are mixing angles in the neutral and charged Higgs sectors, respectively, with tan β given by the ratio of the vaccuum expectation values of the Higgs doublets, tan β = v 2 /v 1. 1 In both MSSM and 2HDM models there is another production process, namely the Higgs pair production, which is complementary to (2) and (3) in the sense that