The Oblique Parameters In Electroweak Theory with Two Massless Higgs Doublets

The oblique parameters $S$ and $T$ are studied in electroweak theory with two massless Higgs doublets. The effect of quadratic dependence on the charged Higgs mass in the parameter $T$ could be cancelled. %when mass differences between the charged and neutral scalars %become large. The constraint on the charged Higgs mass from the parameter $T$ is not so stringent as it was expected. The parameter $S$ can be both positive and negative but it can't take large negative value. We search allowed scalar mass regions for both $S$ and $T$ in the case of two different reference points.