Neutrino and Lepton Physics
Neutrino observables answer different questions: oscillations determine mass-squared splittings and mixing, endpoint kinematics probes an incoherent mass norm, neutrinoless double-beta decay is sensitive to a coherent lepton-number-violating amplitude, cosmology constrains a model-dependent mass sum, and charged-lepton flavor violation tests other operators. This chapter supplies the mass-to-observable chain needed to keep those statements distinct, calculate each one, and combine them without turning an inference into a property of the Lagrangian.
Enter this chapter
Section titled “Enter this chapter”Begin with Dirac, Majorana, and Seesaw Neutrino Masses to distinguish lepton-number-preserving and lepton-number-violating masses.
Topics
Section titled “Topics”- Dirac, Majorana, and Seesaw Neutrino Masses — Constructs Dirac, Majorana, and seesaw mass terms.
- Lepton Mixing, PMNS Parameters, and Majorana Phases — Counts physical mixing parameters and Majorana phases.
- Neutrino Oscillations, Coherence, and Matter Effects — Computes interference with coherence and matter effects.
- Absolute Neutrino Mass and Majorana-Sensitive Probes — Separates kinematic, nuclear-decay, and cosmological mass information.
- Charged-Lepton Flavor Violation — Organizes rare charged-lepton transitions by effective operators.
- Leptonic CP Observables and Combined Inference — Combines oscillation and other likelihoods with shared conventions.
How the ideas fit together
Section titled “How the ideas fit together”Oscillations depend on relative propagation phases, hence on mass-squared differences, and cannot fix a common absolute mass scale. Endpoint spectra instead involve an incoherent weighted mass norm, whereas the light-Majorana contribution to neutrinoless double-beta decay involves a coherent sum that can cancel. A weak bound on one therefore need not imply a weak bound on another, and translating a decay limit into a mass statement requires an assumed mechanism and nuclear matrix elements. Particle Data Group 2022, 2023 update, §§ 14.2–14.3, PDF.
Where to go next
Section titled “Where to go next”Continue to Standard Model Assembly and Consistency to assemble the fields, interactions, and independent parameters of the model.
References
Section titled “References”- Particle Data Group. “Neutrino Masses, Mixing, and Oscillations.” In Review of Particle Physics, 2022 edition with 2023 update. PDF.