Neutrinoless Double-Beta Decay: A Roadmap for Matching Theory to Experiment

Abstract

The observation of neutrino oscillations and hence non-zero neutrino masses provided a milestone in the search for physics beyond the Standard Model. But even though we now know that neutrinos are massive, the nature of neutrino masses, i.e., whether they are Dirac or Majorana, remains an open question. A smoking-gun signature of Majorana neutrinos is the observation of neutrinoless double-beta decay, a process that violates the lepton-number conservation of the Standard Model. This white paper focuses on the theoretical aspects of the neutrinoless double-beta decay program and lays out a roadmap for future developments. The roadmap is a multi-scale path starting from high-energy models of neutrinoless double-beta decay all the way to the low-energy nuclear many-body problem that needs to be solved to supplement measurements of the decay rate. The path goes through a systematic effective-field-theory description of the underlying processes at various scales and needs to be supplemented by lattice quantum chromodynamics input. The white paper also discusses the interplay between neutrinoless double-beta decay, experiments at the Large Hadron Collider and results from astrophysics and cosmology in probing simplified models of lepton-number violation at the TeV scale, and the generation of the matter-antimatter asymmetry via leptogenesis. This white paper is prepared for the topical groups TF11 (Theory of Neutrino Physics), TF05 (Lattice Gauge Theory), RF04 (Baryon and Lepton Number Violating Processes), NF03 (Beyond the Standard Model) and NF05 (Neutrino Properties) within the Theory Frontier, Rare Processes and Precision Frontier, and Neutrino Physics Frontier of the U.S. Community Study on the Future of Particle Physics (Snowmass 2021).

Lattice QCD calculation of light sterile neutrino contribution in $0\nu2β$ decay

“…As pointed out by the Snowmass white paper [13], the EFTs that systematically describe 0ν2β decay amplitude in the few-nucleon and pion sector need to be complemented with values for LECs from lattice QCD. Our work serves as one more example for such purpose.…”

“…To further determine the absolute mass of the neutrinos and verify whether the neutrinos are Dirac or Majorana fermions, neutrinoless double beta (0ν2β) decay experiments [3][4][5][6][7][8][9][10][11][12] provide an excellent probe. In the framework of effective field theory (EFT), a roadmap to reach the theoretical determination of the 0ν2β decay amplitude is laid out through a path from the BSM scenarios at high energy towards the nuclear many-body theories at low energy [13]. At the energy of O (1) GeV -O(100) MeV, chiral perturbation theory (χPT) and its extension to the multi-nucleon sector, namely chiral EFT, serve as a bridge to connect quark-level theories and nuclear-level theories [1,[14][15][16][17][18][19][20][21][22].…”

Quantum Simulation for High Energy Physics

“…III for more details). They are also important to evaluate nuclear matrix elements required to analyze experiments looking for neutrinoless double-β decay [227,517], and for direct detection of potential dark-matter particles [228,229].…”

Majorana neutrino mass constraints in the landscape of nuclear matrix elements

“…However, no consensus estimates exist yet for NME fiducial values and covariances, although relevant work is in progress toward this goal [1,30]. Part of the planned strategy involves benchmarking nuclear models for 0νββ decay against a variety of data, coming from related electroweak and strong interaction processes or from nuclear structure [31][32][33].…”