Effectively two-dimensional mechanism of axion and neutrino bremsstrahlung in the interaction of electrons with nuclei in a magnetic field

Axion and neutrino bremsstrahlung from electrons in the processes $e(Ze) to e(Ze)a(nu bar nu )$ is considered within the proposed two-dimensional covariant method for calculating Feynman diagrams in an external magnetic field. General expressions for squared matrix elements, as well as for the probability and power of this radiation, are obtained for a nonrelativistic nondegenerate electron gas. The energy scale f _a characteristic of the violation of global Peccei-Quinn symmetry is constrained by comparing the contributions of the above processes to the emissivity of magnetic neutron stars.