  Considering homogeneous four-dimensional space-time geometries within real
projective geometry provides a mathematically well-defined framework to discuss
their deformations and limits without the appearance of coordinate
singularities. On Lie algebra level the related conjugacy limits act
isomorphically to concatenations of contractions. We axiomatically introduce
projective quantum fields on homogeneous space-time geometries, based on
correspondingly generalized unitary transformation behavior and
projectivization of the field operators. Projective correlators and their
expectation values remain well-defined in all geometry limits, which includes
their ultraviolet and infrared limits. They can degenerate with support on
space-time boundaries and other lower-dimensional space-time subspaces. We
explore fermionic and bosonic superselection sectors as well as the
irreducibility of projective quantum fields. Dirac fermions appear, which obey
spin-statistics as composite quantum fields. The framework systematically
formalizes and generalizes the ambient space techniques regularly employed in
conformal field theory.
