V. Cirigliano, W. Dekens, J. de Vries, M.L. Graesser, E. Mereghetti, S. Pastore, and U. van Kolck,
Phys. Rev. Lett. 120 (2018) 202001

One of the most important advancements in modern particle physics was the observation of neutrino oscillations and the inference that neutrinos have mass. However, the origin of neutrino masses remains a mystery. They can arise from an interaction with the Higgs field that violates lepton number, makes neutrinos Majorana particles, and potentially explains the observed matter-antimatter asymmetry of the universe. This mechanism is only accessible through neutrinoless double-beta decay experiments, where two neutrons in a nucleus turn into two protons, with the emission of two electrons and no neutrinos. Nuclear physics is required for the interpretation of a non-zero signal (or lack thereof) from the enormous experimental effort which is underway around the world.

Based on renormalization arguments, we have now shown that the leading contribution to neutrinoless double-beta decay, where light Majorana neutrinos are exchanged between nucleons, is not well defined without a short-range interaction. This short-range contribution is missing in all current calculations and should eventually be determined from simulations of Quantum Chromodynamics on a spacetime lattice. It can also be estimated, via chiral symmetry, from isospin-breaking observables in the two-nucleon sector. Using existing data for such an estimate, we have shown explicitly in the decay of 12Be that this new short-range contribution can be comparable to model-dependent estimates of the long-range neutrino exchange. This new leading effect could thus significantly affect the neutrino mass properties extracted from double-beta-decay experiments.