2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/50270The motion of spinning relativistic particles in external electromagnetic and gravitational fields is considered. Covariant equations for this motion are demonstrated to possess pathological solutions, when treated nonperturbatively in spin. A self-consistent approach to the problem is formulated, based on the noncovariant description of spin and on the usual, ``naive'' definition of the coordinate of a relativistic particle. A simple description of the gravitational interaction of first order in spin, is pointed out for a relativistic particle. The approach developed allows one to consider effects of higher order in spin. Explicit expression for the second-order Hamiltonian is presented. We discuss the gravimagnetic moment, which is a special spin effect in general relativity.LaTeX, 10 pages, Submitted to Proceedinds of E.S.Fradkin Memorial ConferenceHigh Energy Physics - TheoryGeneral Relativity and Quantum Cosmologytext