Abstract: Nuclei could neutrinoless double-beta (0νββ) decay by emitting two electrons, reaching a final state with two more protons and two fewer neutrons than the initial one. Such a process, therefore, creates two matter particles. This violation of the Standard Model’s lepton number conservation is only possible if neutrinos are their own antiparticles.  0νββ decay remains to be observed, but due to its unique potential to shed light on neutrino properties and physics beyond the Standard Model, worldwide collaborations eagerly pursue its detection.  However, the interpretation of 0νββ experiments depends on nuclear matrix elements that govern the 0νββ decay rate, but these are poorly known. This theoretical uncertainty limits severely the exploitation of 0νββ experiments.

I will present several avenues to overcome this limitation and improve our understanding of 0νββ decay.  On the nuclear experiment side, I will show the potential to learn about 0νββ by measuring double Gamow-Teller transitions in double charge-exchange reactions or electromagnetic double-gamma decays.  On the nuclear theory side, I will discuss a previously neglected short-range matrix element’s contribution that can significantly impact the 0νββ decay rate. In addition, I will present preliminary results which improve traditional matrix element calculations for heavy nuclei, complementing them with ab initio quantum Monte Carlo ones that capture additional nuclear correlations.