One-loop expressions for h → l(l)over-barγ in Higgs extensions of the Standard Model

A systematic study of one-loop contributions to the decay channels h -> l (l) over bar gamma with l = nu(e, mu, t), e, mu, performed in Higgs extended versions of the Standard Model (SM), is presented in the 't Hooft-Veltman gauge. Analytic formulas for one-loop form factors are expressed in terms of the logarithm and di-logarithmic functions. As a result, these form factors can be reduced to those relating to the loop-induced decay processes h -> gamma gamma, Z gamma, confirming not only previous results using different approaches but also close relations between the three kinds of loop-induced Higgs decay rates. For phenomenological study, we focus on the two observables, namely the enhancement factors defined as ratios of the decay rates calculated between the Higgs extended versions and the SM, and the forward-backward asymmetries of fermions, which can be used to search for Higgs extensions of the SM. We show that direct effects of mixing between neutral Higgs bosons and indirect contributions of charged Higgs boson exchanges can be probed at future colliders.