Electron and Positron Capture Rates on $\bf{^{55}}$Co in Stellar Matter

TL;DR

This paper calculates electron and positron capture rates on cobalt-55 in stellar environments using a microscopic pn-QRPA approach, revealing enhanced rates due to larger model space and more realistic assumptions, impacting supernova core collapse models.

Contribution

It introduces a microscopic pn-QRPA method for calculating capture rates on cobalt-55, avoiding Brink's hypothesis, and provides more accurate rates over a wide range of stellar conditions.

Findings

Capture rates are higher than previous shell model estimates.

Large model space allows consideration of more excited states.

Rates are computed over extensive temperature and density ranges.

Abstract

Cobalt-55 is not only present in abundance in presupernova phase but is also advocated to play a decisive role in the core collapse of massive stars. The spectroscopy of electron capture and emitted neutrinos yields useful information on the physical conditions and stellar core composition. B(GT) values to low-lying states are calculated microscopically using the pn-QRPA theory. Our rates are enhanced compared to the shell model rates. The enhancement is attributed partly to the liberty of selecting a huge model space, allowing consideration of many more parent excited states in our rate calculation. Unlike previous calculations, the so-called Brink's hypothesis is not assumed leading to a more realistic estimate of the rates. The electron and positron capture rates are calculated over a wide temperature and density grid.