G = 2 AS THE NATURAL VALUE OF THE TREE-LEVEL GYROMAGNETIC RATIO OF ELEMENTARY-PARTICLES

We implement at the Lagrangian level a "natural" electromagnetic coupling prescription, different from the minimal one, and proposed a long time ago by Weinberg. This prescription yields, for elementary particles of arbitrary-spin, a gyromagnetic ratio g = 2 at the tree level. This value is already known to arise in renormalizable theories for spin 1/2 and spin 1, is suggested by the classical, relativistic equations of the spin polarization, and is also found for arbitrary-spin, charged excitations of the open string.