Expanded calculation of weak-interaction mediated neutrino cooling rates due to ${}^{56}$Ni in stellar matter

Abstract

Accurate estimate of the neutrino cooling rates is required in order to study the various stages of stellar evolution of massive stars. Neutrino losses from proto-neutron stars play a crucial role in deciding whether these stars would be crushed into black holes or explode as supernovae. Both pure leptonic and weak-interaction processes contribute to the neutrino energy losses in stellar matter. At low temperatures and densities, characteristic of the early phase of presupernova evolution, cooling through neutrinos produced via the weak-interaction is important. Proton-neutron quasi-particle random phase approximation (pn-QRPA) theory has recently being used for calculation of stellar weak-interaction rates of $fp$-shell nuclide with success. The lepton-to-baryon ratio ($Y_e$) during early phases of stellar evolution of massive stars changes substantially alone due to electron captures on ${}^{56}$Ni. The stellar matter is transparent to the neutrinos produced during the presupernova evolution of massive stars. These neutrinos escape the site and assist the stellar core in maintaining a lower entropy. Here I present the expanded calculation of weak-interaction mediated neutrino and antineutrino cooling rates due to ${}^{56}$Ni in stellar matter using the pn-QRPA theory. This detailed scale is appropriate for interpolation purposes and of greater utility for simulation codes. The calculated rates are compared against earlier calculations. During the relevant temperature and density regions of stellar matter the reported rates show little differences with the shell model rates and might contribute in fine-tuning of the lepton-to-baryon ratio during the presupernova phases of stellar evolution of massive stars.

Comments: 20 pages, 6 figures and 1 table. arXiv admin note: text overlap with arXiv:1108.1010, arXiv:1203.4344