Neutrino mean free path in neutron star matter with Δ isobars

The \ensuremath{\Delta}-isobar degrees of freedom are taken into account in neutron star matter and their contributions to neutrino mean free paths are evaluated. It is found that the charged-current contributions are comparable to those from the neutral-current reactions. The contributions of \ensuremath{\Delta}-isobars may be a leading sector of neutrino opacities in neutron star matter, but the effects of the process in which the baryon transforms between nucleon and \ensuremath{\Delta} are unimportant.