The effects of delta mesons on the baryonic direct Urca processes in neutron star matter

In the framework of relativistic mean field theory, the relativistic neutrino emissivity of the nucleonic and hyperonic direct Urca processes in the degenerate baryon matter of neutron stars are studied. We investigate particularly the influence of the isovector scalar interaction which is considered by exchanging $\delta$ meson on the nucleonic and hyperonic direct Urca processes. The results indicate that $\delta$ mesons lead to obvious enhancement of the total neutrino emissivity, which must result in more rapid cooling rate of neutron star matter.