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The generic form of spacetime dynamics as a classical gauge field theory hasrecently been derived, based on only the action principle and on the Principleof General Relativity. It was thus shown that Einstein's General Relativity isthe special case where (i) the Hilbert Lagrangian (essentially the Ricciscalar) is supposed to describe the dynamics of the "free" (uncoupled)gravitational field, and (ii) the energy-momentum tensor is that of scalarfields representing real or complex structureless (spin-$0$) particles. Itfollowed that all other source fields---such as vector fields representingmassive and non-massive spin-$1$ particles---need careful scrutiny of theappropriate source tensor. This is the subject of our actual paper: we discussin detail the coupling of the gravitational field with (i) a massive complexscalar field, (ii) a massive real vector field, and (iii) a massless vectorfield. We show that different couplings emerge for massive and non-massivevector fields. The \emph{massive} vector field has the \emph{canonical}energy-momentum tensor as the appropriate source term---which embraces also theenergy density furnished by the internal spin. In this case, the vector fieldsare shown to generate a torsion of spacetime. In contrast, the system of a\emph{massless} and charged vector field is associated with the \emph{metric}(Hilbert) energy-momentum tensor due to its additional $\mathrm{U}(1)$symmetry. Moreover, such vector fields do not generate a torsion of spacetime.The respective sources of gravitation apply for all models of the dynamics ofthe `free' (uncoupled) gravitational field---which do not follow from the gaugeformalism but must be specified based on separate physical reasoning.

Canonical transformation path to gauge theories of gravity II --- Spacetime coupling of spin-0 and spin-1 particle fields