Scalar particle with intrinsic structure in the electromagnetic field in curved space-time

Relativistic theory of the Cox’s scalar not point-like particle with intrinsic structure is developed in the presence of external electromagnetic and gravitational fields; the latter is described by pseudo-Riemannian space-time geometry. It is shown that the generalized Proca-like tensor system of equations of the first order contains non minimal interaction terms through electromagnetic tensor $F_{\beta\alpha}$ and Ricci tensor $R_{\beta\alpha}$. Generalized scalar equation of the Klein–Fock–Gordon type turns out to be much more complicated than the ordinary wave equation.