On the Bargmann–Michel–Telegdi equations, and spin–orbit coupling: A tribute to Raymond Stora

The Bargmann–Michel–Telegdi equations describing the motions of a spinning, charged, relativistic particle endowed with an anomalous magnetic moment in an electromagnetic field, are reconsidered. They are shown to duly stem from the linearization of the characteristic distribution of a presymplectic structure refining the original one of Souriau. In this model, once specialized to the case of a static electric-like field, the angular momentum and energy given by the associated moment map now correctly restore the spin–orbit coupling term. This is the state-of-the-art of unfinished joint work with Raymond Stora