In the Standard Model we have one Higgs doublet corresponding to one physical
Higgs particle. There are several motivations to extend the Higgs sector of
the Standard Model. For instance in supersymmetric extensions of the
Standard Model at least two
Higgs doublets are required. In fact, we have three fermion families - why should
we only have one Higgs doublet?

We have been studying different aspects of
the general Two-Higgs-Doublet Model (THDM). A new formalism, where we introduce
four real bilinear terms in the doublets, turns out to be quite powerfull.
In this formalism the investigation of
stability, stationarity solutions, electroweak symmetry breaking,
CP transformations, and Higgs family symmetries in THDM's
turns out to be possible in a very general und transparent way.
Moreover, it is found that
the bilinear formalism has often a very simple geometric meaning:
for example, generalised CP transformations
correspond to
reflections on planes or to point reflections.

Currently, we are working on special THDM's which
follow from symmetry arguments.

For more informations about our recent research, we
refer to
the Spires listing.