Electromagnetic Aspects of Neutral Elementary Particles in Relativistic Quantum Mechanics

This paper presents viable scenarios in which we can check the possibility that neutral genuinely elementary particles acquire a magnetic dipole moment at quantum-mechanical level and rather than as a loop effect in Quantum Field Theory. We actually have in mind to evaluate the very role of the spin for the magnetic properties of the particles, trying to disconnect spin from electric charge. For that, we adopt the Dirac equation for the description of massive charged, neutral or, eventually, self-conjugated (Majorana-like) fermions. We propose a sistematic study of nonminimal electromagnetic couplings and their consequences, in the non-relativistic regime, on the magnetic dipole moment generation for fermionic particles. The discussion sets out also in situations where Lorentz-symmetry breaking takes place. The investigation is also pursued for massive neutral vector bosons and we contemplate situations in which a non-trivial magnetic moment appears already at the tree-approximation, despite the absence of an electric charge for the particles under consideration.