Mass Matrix Ansatz Research Articles

Flavored axions and the flavor problem

A Peccei-Quinn (PQ) symmetry is proposed, in order to generate in the Standard Model (SM) quark sector a realistic mass matrix ansatz with five texture-zeros. Limiting our analysis to Hermitian mass matrices we show that this requires a minimum of 4 Higgs doublets. This model allows assigning values close to 1 for several Yukawa couplings, giving insight into the origin of the mass scales in the SM. Since the PQ charges are non-universal the model features Flavor-Changing Neutral Currents (FCNC) at the tree level. From the analytical expressions for the FCNC we report the allowed region in the parameter space obtained from the measurements of branching ratios of semileptonic meson decays.

Flavor-changing neutral currents in the Higgs sector

This review considers models with extended Higgs sectors in which there are tree-level flavor-changing neutral currents (FCNC) mediated by scalars. After briefly reviewing models without tree-level FCNC, several models with such currents are discussed. A popular mass-matrix ansatz, in which the flavor-changing couplings are the geometric mean of the individual flavor couplings, is presented. While it provided a target for experimentalists for three decades, it is now being severely challenged by experiments. Couplings expected to be of [Formula: see text] must be substantially smaller and the ansatz is now not favored. The minimal flavor violation hypothesis is introduced. Then specific models are presented, including the Branco–Grimus–Lavoura models. These models are not yet excluded experimentally, but they are highly predictive and will be tested once heavy Higgs bosons are discovered. We then turn to flavorful models and flavor-changing decays of heavy Higgs bosons, and it is shown that in many of these models, the heavy Higgs could predominantly decay in a flavor-changing manner (such as [Formula: see text] or [Formula: see text]) and experimentalists are encouraged to include these possibilities in their searches.

Grand Unified Yukawa Matrix Ansatz: The Standard Model Fermion Mass, Quark Mixing and CP Violation Parameters

We propose a new mass matrix ansatz: At the grand unified (GU) scale, the standard model (SM) Yukawa coupling matrix elements are integer powers of the square root of the GU gauge coupling constant ∊ = √αGU, multiplied by order unity random complex numbers. It relates the hierarchy of the SM fermion masses and quark mixings to the gauge coupling constants, greatly reducing the SM parameters, and can give good fitting results of the SM fermion mass, quark mixing and CP violation parameters. This is a neat but very effective ansatz.

Mass-matrix ansatz and constraints onBs0−B¯s0mixing in 331 models

Comparing the theoretically predicted and measured values of the mass difference of the ${B}_{s}^{0}$ system, we estimate the lower bound on the mass of the ${Z}^{\ensuremath{'}}$ boson of models based on the $SU(3{)}_{c}\ensuremath{\bigotimes}SU(3{)}_{L}\ensuremath{\bigotimes}U(1{)}_{X}$ gauge group. By assuming zero-texture approaches of the quark mass matrices, we find the ratio of the measured value to the theoretical prediction from the standard model and the ${Z}^{\ensuremath{'}}$ contribution from the 331 models of the mass difference of the ${B}_{s}^{0}$ system. We find lower bounds on the ${Z}^{\ensuremath{'}}$ mass ranging between 1 TeV and 30 TeV for the two most popular 331 models, and four different zero-textures ans\"atze. The above results are expressed as a function of the weak angle associated to the $b\ensuremath{-}s\ensuremath{-}{Z}^{\ensuremath{'}}$ couplings.

FERMION MASSES AND MIXING IN FOUR AND MORE DIMENSIONS

We give an overview of recent progress in the study of fermion mass and flavor mixing phenomena. Mass matrix ansatze are considered within the Standard Model (SM) and SUSY GUT's where some predictive frameworks based on SU(5) and SO(10) are reviewed. We describe a variety of schemes to construct quark mass matrices in extra dimensions focusing on four major classes: models with the SM residing on 3-brane, models with universal extra dimensions, models with split fermions and models with warped extra dimensions. We outline how realistic patterns of quark mass matrices could be derived from orbifold models in heterotic superstring theory. Finally, we address the fermion mass problem in intersecting D-branes scenarios, and present models with D6-branes able to give a good quantitatively description of quark masses and mixing. The role of flavor/CP violation problem as a probe of new physics is emphasized.

Quark-lepton complementarity relation and neutrino mass hierarchy

Latest measurements have revealed that the deviation from a maximal solar mixing angle is approximately the Cabibbo angle, i.e. QLC relation. We argue that it is not plausible that this deviation from maximality, be it a coincidence or not, comes from the charged lepton mixing. Consequently we have calculated the required corrections to the exactly bimaximal neutrino mass matrix ansatz necessary to account for the solar mass difference and the solar mixing angle. We point out that the relative size of these two corrections depends strongly on the hierarchy case under consideration. We find that the inverted hierarchy case with opposite CP parities, which is known to guarantee the RGE stability of the solar mixing angle, offers the most plausible scenario for a high energy origin of a QLC-corrected bimaximal neutrino mass matrix. This possibility may allow us to explain the QLC relation in connection with the origin of the charged fermion mass matrices.

Mass matrix ansatz and lepton flavor violation in the two-Higgs doublet model-III

Predictive Higgs-boson--fermion couplings can be obtained when a specific texture for the fermion mass matrices is included in the general two-Higgs doublet model. We derive the form of these couplings in the charged lepton sector using a Hermitian mass matrix ansatz with four-texture zeros. The presence of unconstrained phases in the vertices ${\ensuremath{\varphi}}_{i}{l}_{i}{l}_{j}$ modifies the pattern of flavor-violating Higgs boson interactions. Bounds on the model parameters are obtained from present limits on rare lepton flavor-violating processes, which could be extended further by the search for the decay $\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\tau}}\ensuremath{\mu}\ensuremath{\mu}\ensuremath{\mu}$ and $\ensuremath{\mu}\ensuremath{-}e$ conversion at future experiments. The signal from Higgs boson decays ${\ensuremath{\varphi}}_{i}\ensuremath{\rightarrow}\ensuremath{\tau}\ensuremath{\mu}$ could be searched for at the CERN Large Hadron Collider, while $e\ensuremath{-}\ensuremath{\mu}$ transitions could produce a detectable signal at a future $e\ensuremath{\mu}$ collider, through the reaction ${e}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}\ensuremath{\rightarrow}{h}^{0}\ensuremath{\rightarrow}{\ensuremath{\tau}}^{+}{\ensuremath{\tau}}^{\ensuremath{-}}.$

Higgsino mass matrix ansatz for MSSM

An ansatz, DetMH̃=0, for the Higgsino mass matrix is suggested toward the minimal supersymmetric standard model (MSSM). Small instanton solutions effective around the GUT scale can fulfill this condition. An argument that the couplings contain a moduli field is given for a dynamical realization of this Higgsino mass matrix ansatz. We also present a string orbifold trinification toward this realization.

A natural framework for bi-large neutrino mixing

In this Letter we present a “natural” framework for obtaining bi-large neutrino mixing incorporating the Frampton–Glashow–Yanagida neutrino mass matrix ansatz. We show that an SU(2)×U(1) family symmetry can provide the desired FGY neutrino mass ansatz in a minimal supersymmetric standard model. We also show how to obtain an approximate FGY ansatz in an SO(10) SUSY GUT. In this context, the same SU(2)×U(1) family symmetry also generates the hierarchy of fermion masses as well as ameliorating SUSY flavor problems.

Neutrino masses and leptonicCPviolation

Neutrino oscillations as solutions of the solar neutrino problems and the atmospheric neutrino deficits may restrict neutrino mass squared differences and mixing angles in three-neutrino mixing scheme. Currently we have several solutions depending on the interpretations of the solar neutrino problems. Combining the neutrino oscillation solutions and a mass matrix ansatz, we investigated the neutrino mass bounds and found possible leptonic CP-violating rephasing-invariant quantity $J^{l}_{\tiny CP} \leq 0.012$ for large mixing angle MSW and just-so vacuum oscillations solutions, and $J^{l}_{\tiny CP} \leq 0.0013$ for small mixing angle MSW solution.

Lepton flavor mixing and baryogenesis

Recently a new general class of quark mass matrix ansatz has been proposed, which originates from some flavor symmetry. We extend that symmetry to the lepton sector and study the neutrino mass matrix and address the question of the baryon asymmetry of the universe in this model.

Hierarchical quark mixing and bimaximal lepton mixing on the same footing

We show that not only the hierarchical quark CKM mixing matrix but also the ``bimaximal'' lepton flavor mixing matrix can be derived from the same mass-matrix ansatz based on broken permutation symmetry, by assuming the hierarchy of neutrino masses to be ${m}_{1}\ensuremath{\simeq}{m}_{2}\ensuremath{\ll}{m}_{3}.$ We also reproduce the recently measured angle of the unitary triangle, $\mathrm{sin}2\ensuremath{\beta},$ as well as all the observed experimental values of ${V}_{\mathrm{CKM}}$ of the quark CKM matrix. And we predict the Jarlskog rephasing-invariant quantity ${J}_{\mathrm{CP}}\ensuremath{\simeq}0.18\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ and the upper bound of the same quantity in the lepton sector, ${J}_{\mathrm{CP}}^{l}<~0.012,$ which may be indeed large enough to generate lepton number violation of the universe.

Mass matrix ansatz for degenerate neutrinos consistent with solar and atmospheric neutrino data

We suggest mass matrices for neutrinos and charged leptons that can explain solar and atmospheric neutrino data. The resulting flavor mixing matrix V ν has a property that ( V ν ) 13=0, thus making ν e ↔ ν μ and ν μ ↔ ν τ oscillations to be effectively a two-channel problem. Phenomenological consequences of the lepton mass matrix ansatze are consistent with the current data on various type of neutrino oscillation experiments except the LSND measurement. Three neutrinos, being almost degenerate with ∑ |m ν i |≲1 eV, can be a part of hot dark matter without any conflict with the constraint from neutrinoless double beta decay experiments. The ν μ ↔ ν τ oscillation, sin 22 θ μτ , is predicted to be 0.86–0.97 with Δm 2 μτ≃2×10 −3 eV 2 , which is consistent with the atmospheric neutrino data and can be tested further at the planned MINOS and K2K experiments searching for ν μ → ν τ oscillation.

A four-neutrino mixing scheme for observed neutrino data

It has been observed that simultaneous explanation of the solar and atmospheric neutrino deficits and the reported evidence for $\nu_{\mu}\to \nu_{e}$ oscillation from the Los Alamos Liquid Scintillator Detector (LSND) requires at least one extra neutrino species in addition to the three known ones. The extra neutrino must be sterile with respect to the known weak interactions. We present a new mass matrix for these four neutrinos in which the LSND effect and the atmospheric neutrino deficit are governed by only one parameter. We investigate the phenomenological implications of such a mass matrix ansatz and suggest possible ways to understand it in gauge theories.

New class of quark mass matrix and calculability of the flavor mixing matrix

We discuss a new general class of mass matrix Ansatz that respects the fermion mass hierarchy and calculability of the flavor mixing matrix. This is a generalization and justification of the various specific forms of the mass matrix by successive breaking of the maximal permutation symmetry. By confronting the experimental data, a large class of the mass matrices are shown to survive, while certain specific cases are phenomenologically ruled out. Also the $\mathrm{CP}$ violation turns out to be maximal, when the phase of the (1,2) element of the mass matrix is $\ensuremath{\pi}/2$.

Almost Maximally Broken Permutation Symmetry for Neutrino Mass Matrix

Assuming three light neutrinos are Majorana particles, we propose mass matrix ansatz for the charged leptons and Majorana neutrinos with family symmetry S3 broken into S1 and S2, respectively. Each matrix has three parameters, which are fixed by measured charged lepton masses, differences of squared neutrino masses relevant to the solar and the atmospheric neutrino puzzles, and the masses of three light Majorana neutrinos as a candidate for hot dark matter with ∑|mν|~ 6 eV . The resulting neutrino mixing is compatible with the data for the current upper limit, <mνe> th <0.7 eV , of neutrino-less double beta decay experiments, and the current data for various types of neutrino oscillation experiments. One solution of our model predicts that νμ→ντ oscillation probability is about < 0.008 with Δm2 ~ 10-2 eV 2, which may not be accessible at CHORUS and other on-going experiments.

The Unitarity Triangle on the First Quadrant and the Quark Mass Matrices in the Nearest-Neighbor Interaction Basis

The unitarity triangle on the first quadrant in the $\rho -\eta$ plane is discussed in the framework of the quark mass matrices in the NNI basis. If the quark mass matrices of the up-type is the Fritzsch one and the down-type is the one proposed by Branco et al., respectively, one gets the unitarity triangle with the vertex on the first quadrant. This simple model may be a candidate of the quark mass matrix ansatze, if the allowed region of the vertex of the unitarity triangle is restricted in the first quadrant by future experiments.

ANSATZ FOR QUARK, CHARGED LEPTON, AND NEUTRINO MASSES IN SUSY GUTs

We extend a fermion mass matrix ansatz by Giudice to include neutrino masses. The previous predictions are maintained. With two additional parameters, a large Majorana neutrino mass and a hierarchy factor, we have seven further low energy predictions: the masses of the neutrinos, the mixing angles and the phase in the leptonic sector. We choose a reasonable hierarchy of Majorana masses and fit the overall mass scale according to a solution of the solar neutrino problem via the MSW mechanism, which is in agreement with the 37 Cl , Kamiokande, SAGE and GALLEX data. We then also obtain a cosmologically interesting tau-neutrino mass.

Mass-matrix ansatz and flavor nonconservation in models with multiple Higgs doublets.

Motivated by the existence of three fermion generations, we consider models with three Higgs doublets (for each hypercharge). It is shown that, if the basic Yukawa coupling matrices are of the Fritzsch form or some generalizations thereof (two such examples are presented), then the neutral flavor-changing couplings have a hierarchical structure given by ${\ensuremath{\Delta}}_{\mathrm{ij}}$ \ensuremath{\surd}${m}_{i}$${m}_{j}$ , where ${\ensuremath{\Delta}}_{\mathrm{ij}}$ is a combination of mixing angles and the ${m}_{i}$'s are the relevant fermion masses. These couplings give a lower bound of the order of ${\ensuremath{\Delta}}_{\mathrm{ds}}$ times 1 TeV on the mass of the exchanged scalar from the neutral-kaon mass difference. If the Higgs-boson mass is not significantly greater than this limit, one expects DD\ifmmode\bar\else\textasciimacron\fi{} mixing comparable to the present experimental bound.

Regularities of fermion masses and mixing angles and their extension to the fourth generation.

The success of the Fritzsch mass-matrix Ansatz in reproducing the observed pattern of the Kobayashi-Maskawa mixings can be explained by having the mass matrices of the charge (2/3) and -(1/3) quarks closely proportional to each other. Thus except for light quarks, the ratio of these two masses in each generation should be the same. Extending this to the fourth generation and using the electroweak rho-parameter constraint we expect that the fourth charged lepton, the seventh (down type), and the eighth (up type) quarks, if they exist, are likely to have masses around 25, 60, and 450 GeV, respectively.