Neutral fermion with a magnetic moment in external electromagnetic fields

The interaction between a massive ventral fermion with a static (spin) magnetic dipole moment mu and in external electromagnetic field is described by the Dirac-Pauli equation. Exact solutions of this equation are obtained along with the corresponding energy spectrum fill, ail axially symmetric external magnetic field and for soiree centrally symmetric electric fields. It is shown drat the spin-orbital interaction of a neutral fermion with a magnetic moment determines both the characteristic properties of the quantum states and the fermion energy spectrum. It is found that (1) the discrete energy spectrum of a neutral fermion depends oil the projection of the fermion spin on a certain quantization axis. (2) the ground energy level of a fermion in these electric Fields as is-oil as the energy levels of all bound states with a fixed value of the quantum number characterizing the projection of the fermion spin in the electric Field E = er is degenerate and the degeneration order is countably infinite, and (3) the energy spectra of neutral fermions and antifermions with spin magnetic moments are symmetric in centrally symmetric fields. Bound states of a neutral fermion with a magnetic moment in an external electric field do exist even if the Dirac-Pauli equation does not explicitly contain the term with the fermion mass. In addition, in centrally symmetric electric fields. there exists a countably infinite set of pairs of isolated charge-conjugate zero-energy solutions of the Dirac-Pauli equation.