  In this thesis a model framework for describing baryons as diquark-quark
bound states is presented which is formulated in an explicitly covariant
manner. The relativistic bound state problem for three quarks is considered.
Diquarks are introduced as separable correlations in the two-quark correlation
function and thereby baryons are described by a Bethe-Salpeter equation for
bound states of quark and diquark which interact by quark exchange. In analogy
to the meson spectrum, scalar and axialvector diquarks are considered to be the
most important two-quark configurations within baryons. The numerical solutions
of the covariant Bethe-Salpeter equation are subsequently employed in the
calculation of electromagnetic, strong and axial form factors of the nucleons.
The construction of the electromagnetic current operator in the diquark-quark
model respects gauge invariance. Invariance under chiral symmetry
transformations is slightly violated for vector diquarks have been neglected,
leading to a modest violation of the Goldberger-Treiman relation. The
possibility of an effective parametrization of confinement by suitable
modifications of the quark and diquark propagators is investigated. It is shown
that the modelling of confinement chosen here is suitable for the calculation
of the octet and devuplet spectrum and spacelike nucleon properties, but its
applicability breaks down for processes where large energies are transferred to
the nucleon as it is the case in certain meson production processes. Model
solutions for nucleon wave functions and observables are compared between the
full relativistic treatment and a widely used semi-relativistic approximation.
The considerable deviations in the results illustrate the inadequacy of
employing the semi-relativistic treatment.
