Coupled-Cluster Calculations Of Neutrinoless Double-Beta Decay In Ca-48

We use coupled-cluster theory and nuclear interactions from chiral effective field theory to compute the nuclear matrix element for the neutrinoless double-beta decay of Ca-48. Benchmarks with the no-core shell model in several light nuclei inform us about the accuracy of our approach. For Ca-48 we find a relatively small matrix element. We also compute the nuclear matrix element for the two-neutrino double-beta decay of Ca-48 with a quenching factor deduced from two-body currents in recent ab initio calculation of the Ikeda sum rule in Ca-48 [Gysbers et al., Nat. Phys. 15, 428 (2019)].