Can the Lepton Flavor Mixing Matrix Be Symmetric?

Current neutrino oscillation data indicate that the 3x3 lepton flavor mixing matrix V is likely to be symmetric about its V_{e3}-V_{\mu 2}-V_{\tau 1} axis. This off-diagonal symmetry corresponds to three pairs of {\it congruent} unitarity triangles in the complex plane. Terrestrial matter effects can substantially modify the genuine CP-violating parameter and off-diagonal asymmetries of V in realistic long-baseline experiments of neutrino oscillations.Comment: RexTex 14 pages (4 PS figures). More discussions adde

Massive and Massless Neutrinos on Unbalanced Seesaws

The observation of neutrino oscillations requires new physics beyond the standard model (SM). A SM-like gauge theory with p lepton families can be extended by introducing q heavy right-handed Majorana neutrinos but preserving its SU(2)_L x U(1)_Y gauge symmetry. The overall neutrino mass matrix M turns out to be a symmetric (p+q) x (p+q) matrix. Given p>q, the rank of M is in general equal to 2q, corresponding to 2q non-zero mass eigenvalues. The existence of (p-q) massless left-handed Majorana neutrinos is an exact consequence of the model, independent of the usual approximation made in deriving the Type-I seesaw relation between the effective p x p light Majorana neutrino mass matrix M_\nu and the q x q heavy Majorana neutrino mass matrix M_R. In other words, the numbers of massive left- and right-handed neutrinos are fairly matched. A good example to illustrate this seesaw fair play rule is the minimal seesaw model with p=3 and q=2, in which one massless neutrino sits on the unbalanced seesaw.Comment: RevTex 8 pages, 1 PS figure. Two crucial references adde

More Straightforward Extraction of the Fundamental Lepton Mixing Parameters from Long-Baseline Neutrino Oscillations

We point out the simple reversibility between the fundamental neutrino mixing parameters in vacuum and their effective counterparts in matter. The former can therefore be expressed in terms of the latter, allowing more straightforward extraction of the genuine lepton mixing quantities from a variety of long-baseline neutrino oscillation experiments. In addition to the parametrization-independent results, we present the formulas based on the standard parametrization of the lepton flavor mixing matrix and give a typical numerical illustration.Comment: RevTex 10 pages. Minor changes. Phys. Rev. D in printin

Updated Values of Running Quark and Lepton Masses

Reliable values of quark and lepton masses are important for model building at a fundamental energy scale, such as the Fermi scale M_Z \approx 91.2 GeV and the would-be GUT scale \Lambda_GUT \sim 2 \times 10^16 GeV. Using the latest data given by the Particle Data Group, we update the running quark and charged-lepton masses at a number of interesting energy scales below and above M_Z. In particular, we take into account the possible new physics scale (\mu \sim 1 TeV) to be explored by the LHC and the typical seesaw scales (\mu \sim 10^9 GeV and \mu \sim 10^12 GeV) which might be relevant to the generation of neutrino masses. For illustration, the running masses of three light Majorana neutrinos are also calculated. Our up-to-date table of running fermion masses are expected to be very useful for the study of flavor dynamics at various energy scales.Comment: 23 pages, 6 tables, 2 figures; version published in PR

Neutrino Masses, Lepton Flavor Mixing and Leptogenesis in the Minimal Seesaw Model

We present a review of neutrino phenomenology in the minimal seesaw model (MSM), an economical and intriguing extension of the Standard Model with only two heavy right-handed Majorana neutrinos. Given current neutrino oscillation data, the MSM can predict the neutrino mass spectrum and constrain the effective masses of the tritium beta decay and the neutrinoless double-beta decay. We outline five distinct schemes to parameterize the neutrino Yukawa-coupling matrix of the MSM. The lepton flavor mixing and baryogenesis via leptogenesis are investigated in some detail by taking account of possible texture zeros of the Dirac neutrino mass matrix. We derive an upper bound on the CP-violating asymmetry in the decay of the lighter right-handed Majorana neutrino. The effects of the renormalization-group evolution on the neutrino mixing parameters are analyzed, and the correlation between the CP-violating phenomena at low and high energies is highlighted. We show that the observed matter-antimatter asymmetry of the Universe can naturally be interpreted through the resonant leptogenesis mechanism at the TeV scale. The lepton-flavor-violating rare decays, such as $\mu \to e + \gamma$, are also discussed in the supersymmetric extension of the MSM.Comment: 50 pages, 22 EPS figures, macro file ws-ijmpe.cls included, accepted for publication in Int. J. Mod. Phys.

Image tag completion by local learning

The problem of tag completion is to learn the missing tags of an image. In this paper, we propose to learn a tag scoring vector for each image by local linear learning. A local linear function is used in the neighborhood of each image to predict the tag scoring vectors of its neighboring images. We construct a unified objective function for the learning of both tag scoring vectors and local linear function parame- ters. In the objective, we impose the learned tag scoring vectors to be consistent with the known associations to the tags of each image, and also minimize the prediction error of each local linear function, while reducing the complexity of each local function. The objective function is optimized by an alternate optimization strategy and gradient descent methods in an iterative algorithm. We compare the proposed algorithm against different state-of-the-art tag completion methods, and the results show its advantages

D^0-\bar{D}^0 Mixing and CP Violation in Neutral D-meson Decays

D^0-\bar{D}^0 mixing at the detectable level or significant CP violation in the charm system may strongly signify the existence of new physics. In view of the large discovery potential associated with the fixed target experiments, the B-meson factories and the \tau-charm factories, we make a further study of the phenomenology of D^0-\bar{D}^0 mixing and CP violation in neutral $D$-meson decays. The generic formulas for the time-dependent and time-integrated decay rates of both coherent and incoherent D^0\bar{D}^0 events are derived, and their approximate expressions up to the second order of the mixing parameters x_D and y_D are presented. Explicitly we discuss D^0-\bar{D}^0 mixing and various CP-violating signals in neutral D decays to the semileptonic final states, the hadronic CP eigenstates, the hadronic non-CP eigenstates and the CP-forbidden states. A few non-trivial approaches to the separate determination of x_D and y_D and to the demonstration of direct and indirect CP asymmetries in the charm sector are suggested.Comment: Latex 42 pages (including 6 PS figures). Minor changes: a) the more popular notation for D^0-\bar{D}^0 mixing is adopted; b) the possibility to test CPT symmetry in D^0-\bar{D}^0 system is not overrated. The present version is going to appear in Phys. Rev. D 1 (January 1997

Exploring the parameter space of texture 4 zero quark mass matrices

We have attempted to extend the parameter space of the elements of the texture 4 zero Hermitian quark mass matrices, to include the case of `weak hierarchy' amongst them along with the usually considered `strong hierarchy' case. This has been carried out by giving wide variation to the hierarchy defining parameters D_U and D_D, having implications for the structural features of the mass matrices. We find that not only the weakly hierarchical mass matrices are able to reproduce the strongly hierarchical mixing angles but also both the phases having their origin in the mass matrices have to be non zero to achieve compatibility of these matrices with recent quark mixing data. Further noting the difference between the exclusive and inclusive values of V_ub, we have carried out separate analyses corresponding to these.Comment: 13 pages, 4 figures, version accepted for publication in Journal Of Physics

A full parametrization of the 6 X 6 flavor mixing matrix in the presence of three light or heavy sterile neutrinos

In addition to three active neutrinos, one or more light sterile neutrinos have been conjectured to account for the LSND, MiniBooNE and reactor antineutrino anomalies (at the sub-eV mass scale) or for warm dark matter in the Universe (at the keV mass scale). Heavy Majorana neutrinos at or above the TeV scale have also been assumed in some seesaw models. Such hypothetical particles can weakly mix with active neutrinos, and thus their existence can be detected at low energies. In the (3+3) scenario with three sterile neutrinos we present a full parametrization of the 6 X 6 flavor mixing matrix in terms of fifteen rotation angles and fifteen phase angles. We show that this standard parametrization allows us to clearly describe the salient features of some problems in neutrino phenomenology, such as (a) possible contributions of light sterile neutrinos to the tritium beta decay and neutrinoless double-beta decay; (b) leptonic CP violation and deformed unitarity triangles of the 3 X 3 flavor mixing matrix of three active neutrinos; (c) a reconstruction of the 6 X 6 neutrino mass matrix in the type-(I+II) seesaw mechanism; and (d) flavored and unflavored leptogenesis scenarios in the type-I seesaw mechanism with three heavy Majorana neutrinos.Comment: RevTex 18 pages, 1 figure. Minor changes, references updated. Accepted for publication in Phys. Rev.