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Benchmark neutrinoless double-beta decay matrix elements in a light nucleus

We compute nuclear matrix elements of neutrinoless double-beta decay mediated by light Majorana-neutrino exchange in the A = 6 system. The goal is to benchmark two many-body approaches, the No-Core Shell Model and the Multi-Reference In-Medium Similarity Renormalization Group. We use the SRG-evolved chiral N3LO-EM500 potential for the nuclear interaction, and make the approximation that isospin is conserved. We compare the results of the two approaches as a function of the cutoff on the many-body basis space. Although differences are seen in the predicted nuclear radii, the ground-state energies and neutrinoless double-beta decay matrix elements produced by the two approaches show significant agreement. We discuss the implications for calculations in heavier nuclei.