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Theory of Neutrinos: A White Paper

R. N. Mohapatra, S. Antusch, K. S. Babu, G. Barenboim, M. -C. Chen, S. Davidson, A. de Gouvea, P. de Holanda, B. Dutta, Y. Grossman, A. Joshipura, B. Kayser, J. Kersten, Y. Y. Keum, S. F. King, P. Langacker, M. Lindner, W. Loinaz, I. Masina, I. Mocioiu, S. Mohanty, H. Murayama, S. Pascoli, S. T. Petcov, A. Pilaftsis, P. Ramond, M. Ratz, W. Rodejohann, R. Shrock, T. Takeuchi, T. Underwood, L. Wolfenstein

TL;DR

This white paper surveys the theory of neutrinos, arguing that oscillations demonstrate nonzero masses and flavor mixing with potential Majorana nature, sterile states, and CP violation. It reviews theoretical frameworks for small neutrino masses, including Seesaw mechanisms (Type I and II), triplet variants, and LR/SO(10) unification, as well as alternative explanations and their phenomenology, such as LFV. It discusses experimental and observational probes of the absolute mass scale and mass hierarchy, including ββ0ν searches, beta-decay endpoints, and cosmology, and emphasizes the need to distinguish Dirac vs Majorana neutrinos and to test nonstandard interactions. It connects neutrino properties to cosmology and the origin of matter via leptogenesis and outlines a roadmap for future experiments and theory. Planck, KATRIN, and next-gen oscillation experiments are highlighted as key tests of the neutrino mass mechanism.

Abstract

During 2004, four divisions of the American Physical Society commissioned a study of neutrino physics to take stock of where the field is at the moment and where it is going in the near and far future. Several working groups looked at various aspects of this vast field. The summary was published as a main report entitled ``The Neutrino Matrix'' accompanied by short 50 page versions of the report of each working group. Theoretical research in this field has been quite extensive and touches many areas and the short 50 page report provided only a brief summary and overview of few of the important points. The theory discussion group felt that it may be of value to the community to publish the entire study as a white paper and the result is the current article. After a brief overview of the present knowledge of neutrino masses and mixing and some popular ways to probe the new physics implied by recent data, the white paper summarizes what can be learned about physics beyond the Standard Model from the various proposed neutrino experiments. It also comments on the impact of the experiments on our understanding of the origin of the matter-antimatter asymmetry of the Universe and the basic nature of neutrino interactions as well as the existence of possible additional neutrinos. Extensive references to original literature are provided.

Theory of Neutrinos: A White Paper

TL;DR

This white paper surveys the theory of neutrinos, arguing that oscillations demonstrate nonzero masses and flavor mixing with potential Majorana nature, sterile states, and CP violation. It reviews theoretical frameworks for small neutrino masses, including Seesaw mechanisms (Type I and II), triplet variants, and LR/SO(10) unification, as well as alternative explanations and their phenomenology, such as LFV. It discusses experimental and observational probes of the absolute mass scale and mass hierarchy, including ββ0ν searches, beta-decay endpoints, and cosmology, and emphasizes the need to distinguish Dirac vs Majorana neutrinos and to test nonstandard interactions. It connects neutrino properties to cosmology and the origin of matter via leptogenesis and outlines a roadmap for future experiments and theory. Planck, KATRIN, and next-gen oscillation experiments are highlighted as key tests of the neutrino mass mechanism.

Abstract

During 2004, four divisions of the American Physical Society commissioned a study of neutrino physics to take stock of where the field is at the moment and where it is going in the near and far future. Several working groups looked at various aspects of this vast field. The summary was published as a main report entitled ``The Neutrino Matrix'' accompanied by short 50 page versions of the report of each working group. Theoretical research in this field has been quite extensive and touches many areas and the short 50 page report provided only a brief summary and overview of few of the important points. The theory discussion group felt that it may be of value to the community to publish the entire study as a white paper and the result is the current article. After a brief overview of the present knowledge of neutrino masses and mixing and some popular ways to probe the new physics implied by recent data, the white paper summarizes what can be learned about physics beyond the Standard Model from the various proposed neutrino experiments. It also comments on the impact of the experiments on our understanding of the origin of the matter-antimatter asymmetry of the Universe and the basic nature of neutrino interactions as well as the existence of possible additional neutrinos. Extensive references to original literature are provided.

Paper Structure

This paper contains 24 sections, 12 equations, 2 figures, 2 tables.

Table of Contents

  1. Introduction
  2. Our present knowledge about masses and mixings
  3. Dirac versus Majorana Neutrinos
  4. Neutrino mixings
  5. Matter effect on neutrino propagation
  6. Neutrino masses
  7. Overall scale for masses
  8. Neutrino masses and neutrinoless double beta decay
  9. Cosmology and neutrino masses
  10. CP violation
  11. Prospects for determining whether neutrinos are Majorana or Dirac
  12. Sterile neutrinos
  13. Neutrino electromagnetic dipole moments and neutrino decay
  14. Neutrino electromagnetic dipole moments and neutrino decay
  15. Neutrino probes of other fundamental symmetries
  16. ...and 9 more sections

Figures (2)

  • Figure 1: The three light neutrino masses as a function of the lightest mass for the normal (left plot) and inverted (right plot) hierarchy.
  • Figure :