An Interdisciplinary Journal

* 2007, Vol.10, No.4, pp.347-357*

The Two-Higgs-Doublet Model is considered, in its CP-non-conserving version.
It is shown quantitatively how vacuum stability and tree-level unitarity in
the Higgs-Higgs-scattering sector constrain the parameter space of the model.
In particular, at high values of tan
,
the model violates unitarity,
unless some of the Higgs bosons are heavy. In the regime of large CP violation
in the neutral-Higgs-*t*-quark sector, which requires tan
, the
Yukawa coupling parameter space (determined by the neutral-Higgs-sector
rotation matrix) is reasonably unconstrained. On the other hand, the
corresponding neutral-Higgs-*b*-quark sector allows for large CP violation at
tan .
However, here the model is more constrained: Significant CP
violation is correlated with a considerable splitting among the two heavier
Higgs bosons.

*Key words: *
vacuum stability, two-Higgs-doublet model, CP violation, unitarity

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Last updated: *January 16, 2008*