Neutrino Mass and New Physics

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.Comment: 90 pages and 9 figures; With permission from the Annual Review of Nuclear and Particle Science. Final version of this material is scheduled to appear in the Annual Review of Nuclear and Particle Science Vol. 56, to be published in November 2006 by Annual Reviews (http://www.annualreviews.org); some references and parts of text update

Screening of Dirac flavor structure in the seesaw and neutrino mixing

We consider the mechanism of screening of the Dirac flavor structure in the context of the double seesaw mechanism. As a consequence of screening, the structure of the light neutrino mass matrix, m_\nu, is determined essentially by the structure of the (Majorana) mass matrix, M_S, of new super-heavy (Planck scale) neutral fermions S. We calculate effects of the renormalization group running in order to investigate the stability of the screening mechanism with respect to radiative corrections. We find that screening is stable in the supersymmetric case, whereas in the standard model it is unstable for certain structures of M_S. The screening mechanism allows us to reconcile the (approximate) quark-lepton symmetry and the strong difference of the mixing patterns in the quark and lepton sectors. It opens new possibilities to explain a quasi-degenerate neutrino mass spectrum, special ``neutrino'' symmetries and quark-lepton complementarity. Screening can emerge from certain flavor symmetries or Grand Unification.Comment: 27 pages, 3 figures; references added, discussion of the E6 model modifie

Neutrino oscillations: Entanglement, energy-momentum conservation and QFT

We consider several subtle aspects of the theory of neutrino oscillations which have been under discussion recently. We show that the $S$-matrix formalism of quantum field theory can adequately describe neutrino oscillations if correct physics conditions are imposed. This includes space-time localization of the neutrino production and detection processes. Space-time diagrams are introduced, which characterize this localization and illustrate the coherence issues of neutrino oscillations. We discuss two approaches to calculations of the transition amplitudes, which allow different physics interpretations: (i) using configuration-space wave packets for the involved particles, which leads to approximate conservation laws for their mean energies and momenta; (ii) calculating first a plane-wave amplitude of the process, which exhibits exact energy-momentum conservation, and then convoluting it with the momentum-space wave packets of the involved particles. We show that these two approaches are equivalent. Kinematic entanglement (which is invoked to ensure exact energy-momentum conservation in neutrino oscillations) and subsequent disentanglement of the neutrinos and recoiling states are in fact irrelevant when the wave packets are considered. We demonstrate that the contribution of the recoil particle to the oscillation phase is negligible provided that the coherence conditions for neutrino production and detection are satisfied. Unlike in the previous situation, the phases of both neutrinos from $Z^0$ decay are important, leading to a realization of the Einstein-Podolsky-Rosen paradox.Comment: 30 pages, 3 eps figures; presentation improved, clarifications added. To the memory of G.T. Zatsepi

Natural relations among physical observables in the neutrino mass matrix

We find all possible relations among physical observables arising from neutrino mass matrices that describe in a natural way the currently observed pattern (tan_23 and tan_12 large, dm^2_Sun/dm^2_Atm and tan_13 small) in terms of a minimum number of parameters. Natural here means due only to the relative smallness (vanishing) of some parameters in the relevant lagrangian, without special relations or accidental cancellations among them.Comment: 14 pages, 1 eps figur

Neutrino Oscillations in a Supersymmetric SO(10) Model with Type-III See-Saw Mechanism

The neutrino oscillations are studied in the framework of the minimal supersymmetric SO(10) model with Type-III see-saw mechanism by additionally introducing a number of SO(10) singlet neutrinos. The light Majorana neutrino mass matrix is given by a combination of those of the singlet neutrinos and the $SU(2)_L$ active neutrinos. The minimal SO(10) model gives an unambiguous Dirac neutrino mass matrix, which enables us to predict the masses and the other parameters for the singlet neutrinos. These predicted masses take the values accessible and testable by near future collider experiments under the reasonable assumptions. More comprehensive calculations on these parameters are also given.Comment: 14 pages, 5 figures; the version to appear in JHE

Neutrino masses from operator mixing

We show that in theories that reduce, at the Fermi scale, to an extension of the standard model with two doublets, there can be additional dimension five operators giving rise to neutrino masses. In particular there exists a singlet operator which can not generate neutrino masses at tree level but generates them through operator mixing. Under the assumption that only this operator appears at tree level we calculate the neutrino mass matrix. It has the Zee mass matrix structure and leads naturally to bimaximal mixing. However, the maximal mixing prediction for solar neutrinos is very sharp even when higher order corrections are considered. To allow for deviations from maximal mixing a fine tuning is needed in the neutrino mass matrix parameters. However, this fine tuning relates the departure from maximal mixing in solar neutrino oscillations with the neutrinoless double beta decay rate.Comment: 11 pages, 1 figure, revte

R-parity-violating SUSY and CP violation in B --> phi K_s

Recent measurements of CP asymmetry in B --> phi K_S appear to be inconsistent with Standard Model expectations. We explore the effect of R-parity-violating SUSY to understand the data.Comment: Equations corrected. Conclusions unchanged. Latex, 6 pages, one fi

Can Measurements of Electric Dipole Moments Determine the Seesaw Parameters?

In the context of the supersymmetrized seesaw mechanism embedded in the Minimal Supersymmetric Standard Model (MSSM), complex neutrino Yukawa couplings can induce Electric Dipole Moments (EDMs) for the charged leptons, providing an additional route to seesaw parameters. However, the complex neutrino Yukawa matrix is not the only possible source of CP violation. Even in the framework of Constrained MSSM (CMSSM), there are additional sources, usually attributed to the phases of the trilinear soft supersymmetry breaking couplings and the mu-term, which contribute not only to the electron EDM but also to the EDMs of neutron and heavy nuclei. In this work, by combining bounds on various EDMs, we analyze how the sources of CP violation can be discriminated by the present and planned EDM experiments.Comment: 26 pages, 9 figures; added reference

Effects of quantum space time foam in the neutrino sector

We discuss violations of CPT and quantum mechanics due to interactions of neutrinos with space-time quantum foam. Neutrinoless double beta decay and oscillations of neutrinos from astrophysical sources (supernovae, active galactic nuclei) are analysed. It is found that the propagation distance is the crucial quantity entering any bounds on EHNS parameters. Thus, while the bounds from neutrinoless double beta decay are not significant, the data of the supernova 1987a imply a bound being several orders of magnitude more stringent than the ones known from the literature. Even more stringent limits may be obtained from the investigation of neutrino oscillations from active galactic nuclei sources, which have an impressive potential for the search of quantum foam interactions in the neutrino sector.Comment: 5 page

New-Physics Effects on Triple-Product Correlations in Lambda_b Decays

We adopt an effective-lagrangian approach to compute the new-physics contributions to T-violating triple-product correlations in charmless Lambda_b decays. We use factorization and work to leading order in the heavy-quark expansion. We find that the standard-model (SM) predictions for such correlations can be significantly modified. For example, triple products which are expected to vanish in the SM can be enormous (~50%) in the presence of new physics. By measuring triple products in a variety of Lambda_b decays, one can diagnose which new-physics operators are or are not present. Our general results can be applied to any specific model of new physics by simply calculating which operators appear in that model.Comment: 20 pages, LaTeX, no figures. Added a paragraph (+ references) discussing nonfactorizable effects. Conclusions unchange