Two-Higgs-doublet models and enhanced rates for a 125 GeV Higgs

We examine the level of enhancement that can be achieved in the ZZ and gamma gamma channels for a two-Higgs-doublet model Higgs boson (either the light h or the heavy H) with mass near 125 GeV after imposing all constraints from LEP data, B physics, precision electroweak data, vacuum stability, unitarity and perturbativity. The latter constraints restrict substantially the possibilities for enhancing the gg -> h -> gamma gamma or gg -> H -> gamma gamma signal relative to that for the SM Higgs, h(SM). Further, we find that a large enhancement of the gg -> h -> gamma gamma or gg -> H -> gamma gamma signal in Type II models is possible only if the gg -> h -> ZZ or gg -> H -> ZZ mode is even more enhanced, a situation disfavored by current data. In contrast, in the Type I model one can achieve enhanced rates in the gamma gamma final state for the h while having the ZZ mode at or below the SM rate - the largest [gg -> h -> gamma gamma]/[gg -> h(SM) -> gamma gamma] ratio found is of order similar to 1.3 when the two Higgs doublet vacuum expectation ratio is tan beta = 4 or 20 and the charged Higgs boson has its minimal LEP-allowed value of m(H)perpendicular to = 90 GeV.