A detailed analysis of a Stueckelberg extension of the electro-weak gauge
group with an extra U(1) factor is presented for the Standard Model as well as
for the MSSM. The extra gauge boson gets massive through a Stueckelberg type
coupling to a pseudo-scalar, instead of a Higgs effect. This new massive
neutral gauge boson Z' has vector and axial vector couplings uniquely different
from those of conventional extra abelian gauge bosons, such as appear e.g. in
GUT models. The extended MSSM furthermore contains two extra neutralinos and
one extra neutral CP-even scalar, the latter with a mass larger than that of
the Z'. One interesting scenario that emerges is an LSP that is dominantly
composed out of the new neutralinos, leading to a possible new superweak
candidate for dark matter. We investigate signatures of the Stueckelberg
extension at a linear collider and discuss techniques for the detection of the
expected sharp Z' resonance. It turns out that the substantially modified
forward-backward asymmetry around the Z' pole provides an important signal.
Furthermore, we also elaborate on generalizations of the minimal Stueckelberg
extension to an arbitrary number of extra U(1) gauge factors.Comment: 49 pages, 13 figures; to appear in JHE
