  Gravitational gauge theories with de Sitter, Poincare and affine symmetry
group are investigated under the aspect of the breakdown of the initial
symmetry group down to the Lorentz subgroup. We review the theory of
spontaneously broken de Sitter gravity by Stelle and West and apply a similar
approach to the case of the Poincare and affine groups. Especially, we find
that the groundstate of the metric affine theory leads to the determination of
the Lorentzian signature of the metric in the groundstate. We show that the
Higgs field remains in its groundstate, i.e., that the metric will have
Lorentzian signature, unless we introduce matter fields that explicitely couple
to the symmetric part of the connection. We also show that some features, like
the necessity of the introduction of a dilaton field, that seem artificial in
the context of the affine theory, appear most natural if the gauge group is
taken to be the special linear group in five dimensions. Finally, we present an
alternative model which is based on the spinor representation of the Lorentz
group and is especially adopted to the description of spinor fields in a
general linear covariant way, without the use of the infinite dimensional
representations which are usually considered to be unavoidable.
