Ab Initio Calculations of β-Decay Half-Lives for N=50 Neutron-Rich Nuclei

β-decay rates of extreme neutron-rich nuclei remain largely unknown experimentally, while they are critical inputs for r-process nucleosynthesis. We present first ab initio calculations of total β-decay half-lives, with a focus on N=50 nuclei. Starting from nuclear forces and currents based on chiral effective field theory, we use the in-medium similarity renormalization group to consistently derive valence-space Hamiltonians and weak operators, from which we calculate the nuclear states involved and the Gamow-Teller transition strengths, without phenomenological adjustments. In addition, we explore effects of first-forbidden contributions. Our results show that the inclusion of two-body currents increases the total half-lives, which then show good agreement with the existing experimental data, thereby validating the predictive capability of our approach.