IMPACT OF MEDIUM EFFECTS ON THE COOLING OF NON-SUPERFLUID AND SUPERFLUID NEUTRON-STARS

Neutrino emission from the dense hadronic component in neutron stars i s subject to strong modifications due to collective effects in the nuc lear medium. We implement new estimates of the neutrino emissivities o f two processes operating in the nuclear medium into numerical cooling simulations of neutron stars. The first process is the modified Urea process, for which the softening of the pion exchange mode and other p olarization effects as well as the neutrino emission arising from the intermediate reaction states are taken into account. The second proces s concerns neutrino emission through superfluid pair breaking and form ation processes. It is found that the medium effects on the emissivity of the modified Urea process result in a strong density dependence, w hich gives a smooth crossover from the standard to the nonstandard coo ling scenario for increasing star masses. For superfluid stars, the su perfluid pair breaking and formation processes accelerate mildly both the standard and the nonstandard cooling scenario. This leads to a goo d agreement between the theoretical cooling tracks and the rather low temperatures observed for objects like PSRs 0833-45 (Vela), 0656+14, a nd 0630+18 (Geminga). The robustness of our findings against variation s in both the underlying equation of state of baryonic matter and the used fast cooling processes is demonstrated. Hence we conclude that th e two recalculated neutrino emissivities studied here enable one to re produce theoretically most of the observed pulsar temperatures by vary ing the masses of neutron star models.