Gamow-Teller (GT$\pm$) strength distributions of $^{56}Ni$ for ground and excited states

Abstract

Gamow-Teller (GT) transitions play an important and consequential role in many astrophysical phenomena. These include, but are not limited to, electron and positron capture rates which determine the fate of massive stars and play an intricate role in the dynamics of core collapse. These $GT_{\pm}$ transitions rates are the significant inputs in the description of supernova explosions. $GT_{\pm}$ strength function values are sensitive to the $^{56}Ni$ core excitation in the middle \textit{pf}-shell region and to the size of the model space as well. We used the pn-QRPA theory for extracting the GT strength for ground and excited states of $^{56}Ni$. We then used these GT strength distributions to calculate the electron \textit{and} positron capture rates which show differences with the earlier calculations. One curious finding of this paper is our enhanced electron capture rates on $^{56}Ni$ at presupernova temperatures. These differences need to be taken into account for the modeling of the early stages of Type II supernova evolution.