Neutrino Mass and New Physics

Abstract

We review the present state of and future outlook for our understanding of neutrino masses and mixings. We discuss what we think are the most important perspectives on the plausible and natural scenarios for neutrinos and what may have the most promise to throw light on the flavor problem of quarks and leptons. We focus on the seesaw mechanism which fits into the big picture of particle physics such as supersymmetry and grand unification providing a unified approach to flavor problem of quarks and leptons. We argue that in combination with family symmetries, this may be at the heart of a unified understanding of flavor puzzle. We also discuss other new physics ideas such as neutrinos in models with extra dimensions and possible theoretical implications of sterile neutrinos. We outline some tests for the various schemes.

Figures (9)

• Figure 1: The best-fit values and the allowed regions of lepton mixing angle $\theta_{12}$ at different confidence levels determined by different groups. From SNO (from ref.homestake), SV sv and Bari bari. Shown are predictions from quark-lepton complementarity (QLC) and tri-bimaximal mixing (see secs. 4,5).
• Figure 2: The best-fit values and the allowed regions of $\sin^2 \theta_{23}$ at different confidence levels determined by different groups: SK atm, GMS concha, Bari bari. Shown are expectations from QLC (sec. 5) and sensitivity limit of T2K experiment T2K.
• Figure 3: The best-fit values and allowed regions of $\sin^2\theta_{13}$ at different confidence levels determined by different groups: SV sv and Bari bari. Shown are also some theoretical predictions and sensitivity limits of Double CHOOZ DC and T2K T2K.
• Figure 4: The 99% C.L. range for $m_{ee}$ as a function of the lightest neutrino mass for the normal ($\Delta m_{23}^2 > 0$) and inverted ($\Delta m_{23}^2 < 0$) mass hierarchies. The darker regions show the allowed range for the present best-fit values of the parameters with negligible errors; from sv.
• Figure 5: Neutrino mass and flavor spectra for the normal (left) and inverted (right) mass hierarchies. The distribution of flavors (colored parts of boxes) in the mass eigenstates corresponds to the best-fit values of mixing parameters and $\sin^2 \theta_{13} = 0.05$.