2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/36112The Minkowski space of special relativity can be understood as a flat 4-dimensional affine space enriched by a constant Minkowski metric. If we gauge the general affine group and `superimpose' the metric, then we arrive at the metric-affine theory of gravity (MAG). The gravitational potentials are the spacetime coframe, the metric, and the linear connection. The material energy-momentum is coupled to the coframe (and the metric), a hypothetical hypermomentum current to the connection. The hypermomentum splits in a spin, a dilation, and a shear piece. We collect some evidence in favor of the existence of a material shear current in the context of Regge type trajectories of `hadronic' matter, thus supporting the link between particle physics and MAG.Latex, mprocl.sty, 3 pages. Contribution to 8th Marcel Grossmann meeting, Jerusalem 1997General Relativity and Quantum Cosmologytext