  We use the field theoretical model to perform relativistic calculations of
neutrino energy losses caused by the direct Urca processes on nucleons in the
degenerate baryon matter. By our analysis, the direct neutron decay in the
superdense nuclear matter under beta equilibrium is open only due to the
isovector meson fields, which create a large energy gap between protons and
neutrons in the medium. Our expression for the neutrino energy losses, obtained
in the mean field approximation, incorporates the effects of nucleon recoil,
parity violation, weak magnetism, and pseudoscalar interaction. For numerical
testing of our formula, we use a self-consistent relativistic model of the
multicomponent baryon matter. The relativistic emissivity of the direct Urca
reactions is found substantially larger than predicted in the non-relativistic
approach. We found that, due to weak magnetism effects, relativistic
emissivities increase by approximately 40-50%, while the pseudoscalar
interaction only slightly suppresses the energy losses, approximately by 5%.
