2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/189412Three-body systems of scalar bosons are described in the framework of relativistic constraint dynamics. With help of a change of variables followed by a change of wave function, two redundant degrees of freedom get eliminated and the mass-shell constraints can be reduced to a three-dimensional eigenvalue problem. In general, this problem is complicated, but for three equal masses a drastic simplification arises at the first post-Galilean order: the reduced wave equation becomes tractable, and we can compute a first-order correction beyond the nonrelativistic limit. The harmonic interaction is displayed as a toy model.16 pages, no figure. Several points clarified, one typo corrected. References added. To appear in Physical Review AHigh Energy Physics - Theorytext