arXiv subjects

Carl H. Albright

Publications and source records attributed to Carl H. Albright.

At least 19 recordsLinked to original sources

arXiv2016

Unification of gauge, family, and flavor symmetries illustrated in gauged SU(12) models

To explain quark and lepton masses and mixing angles, one has to extend the standard model, and the usual practice is to put the quarks and leptons into irreducible representations of discrete groups. We argue that discrete flavor symmetries (and their concomitant problems) can be avoided if we extend the gauge group. In the framework of SU(12) we give explicit examples of models having varying degrees of predictability obtained by scanning over groups and representations and identifying cases with operators contributing to mass and mixing matrices that need little fine- tuning of prefactors. Fitting with quark and lepton masses run to the GUT scale and known mixing angles allows us to make predictions for the neutrino masses and hierarchy, the octant of the atmospheric mixing angle, leptonic CP violation, Majorana phases, and the effective mass observed in neutrinoless double beta decay.

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arXiv2012

An Explicit SU(12) Family and Flavor Unification Model

An explicit SUSY SU(12) unification model with three light chiral families is presented which avoids any external flavor symmetries. The hierarchy of quark and lepton masses and mixings is explained by higher dimensional Yukawa interactions involving Higgs bosons containing SU(5) singlet fields with VEVs appearing at or below the SUSY GUT scale of 2 \times 10^{16} GeV, approximately 50 times smaller than the SU(12) unification scale. The model has been found to be in good agreement with the observed quark and lepton masses and mixings, with nearly all prefactors of O(1) in the four Dirac and one Majorana fermion mass matrices.

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arXiv2012

An explicit SU(12) family and flavor unification model with natural fermion masses and mixings

We present an SU(12) unification model with three light chiral families, avoiding any external flavor symmetries. The hierarchy of quark and lepton masses and mixings is explained by higher dimensional Yukawa interactions involving Higgs bosons that contain SU(5) singlet fields with VEVs about 50 times smaller than the SU(12) unification scale. The presented model has been analyzed in detail and found to be in very good agreement with the observed quark and lepton masses and mixings.

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arXiv2010

Possible Alternatives to Tri-bimaximal Mixing

Possible alternatives to tri-bimaximal mixing are presented based on other symmetry principles, and their predictions for |U_{e3}|, sin^2 theta_{12} and sin^2 theta_{23} are compared to the present neutrino mixing data. In some cases perturbations are required to give better agreement with the data, and the use of a minimal approach is illustrated. Precise experimental determinations of the mixing parameters will be required to decipher the correct mixing pattern and to pin down the appropriate flavor symmetry.

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arXiv2009

Overview of Neutrino Mixing Models and Their Mixing Angle Predictions

An overview of neutrino-mixing models is presented with emphasis on the types of horizontal flavor and vertical family symmetries that have been invoked. Distributions for the mixing angles of many models are displayed. Ways to differentiate among the models and to narrow the list of viable models are discussed.

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arXiv2009

Comparing Trimaximal Mixing and Its Variants with Deviations from Tri-bimaximal Mixing

We analyze in detail the predictions of "trimaximal" neutrino mixing, which is defined by a mixing matrix with identical second column elements. This column is therefore identical to the second column in the case of tri-bimaximal mixing. We also generalize trimaximal mixing by assuming that the other rows and columns of the mixing matrix individually have the same forms as for tri-bimaximal mixing. The phenomenology of these new mixing scenarios is studied. We emphasize how trimaximal mixings can be distinguished experimentally from broken tri-bimaximal mixing.

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arXiv2009

Overview of Neutrino Mixing Models and Ways to Differentiate among Them

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arXiv2008

Lepton Flavor Violation in Predictive Supersymmetric GUT Models

There have been many theoretical models constructed which aim to explain the neutrino masses and mixing patterns. While many of the models will be eliminated once more accurate determinations of the mixing parameters, especially $\sin^2 2θ_{13}$, are obtained, charged lepton flavor violation (LFV) experiments are able to differentiate even further among the models. In this paper, we investigate various rare LFV processes, such as $\ell_{i} \to \ell_{j} + γ$ and $μ-e$ conversion, in five predictive supersymmetric (SUSY) SO(10) models and their allowed soft-SUSY breaking parameter space in the constrained minimal SUSY standard model. Utilizing the Wilkinson Microwave Anisotropy Probe dark matter constraints, we obtain lower bounds on the branching ratios of these rare processes and find that at least three of the five models we consider give rise to predictions for $μ\to e + γ$ that will be tested by the MEG Collaboration at PSI. In addition, the next generation $μ-e$ conversion experiment has sensitivity to the predictions of all five models, making it an even more robust way to test these models. While generic studies have emphasized the dependence of the branching ratios of these rare processes on the reactor neutrino angle $θ_{13}$ and the mass of the heaviest right-handed neutrino $M_3$, we find very massive $M_3$ is more significant than large $θ_{13}$ in leading to branching ratios near to the present upper limits.

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arXiv2008

Model-Independent Analysis of Tri-bimaximal Mixing -- a Softly-Broken Hidden or an Accidental Symmetry?

To address the issue of whether tri-bimaximal mixing (TBM) is a softly-broken hidden or an accidental symmetry, we adopt a model-independent analysis in which we perturb a neutrino mass matrix leading to TBM in the most general way but leave the three texture zeros of the diagonal charged lepton mass matrix unperturbed. We compare predictions for the perturbed neutrino TBM parameters with those obtained from typical SO(10) grand unified theories with a variety of flavor symmetries. Whereas SO(10) GUTs almost always predict a normal mass hierarchy for the light neutrinos, TBM has a priori no preference for neutrino masses. We find, in particular for the latter, that the value of |U_{e3}| is very sensitive to the neutrino mass scale and ordering. Observation of |U_{e3}|^2 > 0.001 to 0.01 within the next few years would be incompatible with softly-broken TBM and a normal mass hierarchy and would suggest that the apparent TBM symmetry is an accidental symmetry instead. No such conclusions can be drawn for the inverted and quasi-degenerate hierarchy spectra.

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arXiv2008

Differentiating Neutrino Models on the Basis of $θ_{13}$ and Lepton Flavor Violation

We show how models of neutrino masses and mixings can be differentiated on the basis of their predictions for $θ_{13}$ and lepton flavor violation in radiative charged lepton decays and $μ- e$ conversion. We illustrate the lepton flavor violation results for five predictive SO(10) SUSY GUT models and point out the relative importance of their heavy right-handed neutrino mass spectra and $θ_{13}$ predictions.

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arXiv2006

Model Predictions for Neutrino Oscillation Parameters

We have surveyed leptonic and grand unified models of neutrino masses and mixings in the literature which are still viable and give numerical predictions for the reactor angle, $θ_{13}$. The results are of considerable interest in anticipation of the next generation reactor experiments and the possible future need for neutrino factories. Of the 63 models considered which were published or posted on the Archive before June 2006, half predict values of $\sin^2 2θ_{13} \gsim 0.015$, which should yield positive signals for $\barν_e$ disappearance in the reactor experiments planned for the near future. Depending upon the outcome of those experiments, half of the models can be eliminated on the basis of the presence or absence of such an observed $\barν_e$ disappearance signal.

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arXiv2005

Bounds on the Neutrino Mixing Angles and CP Phase for an SO(10) Model with Lopsided Mass Matrices

The bounds on the neutrino mixing angles and CP Dirac phase for an SO(10) model with lopsided mass matrices, arising from the presence of ${\bf 16}_H$ and $\bar{\bf 16}_H$ Higgs representations, are studied by variation of the one real and three unknown complex input parameters for the right-handed Majorana neutrino mass matrix. The scatter plots obtained favor nearly maximal atmospheric neutrino mixing, while the reactor neutrino mixing lies in the range $10^{-5} \lsim \sin^2 θ_{13} \lsim 1 \times 10^{-2}$ with values greater than $10^{-3}$ most densely populated. A rather compelling scenario within the model follows, if we restrict the three unknown complex parameters to their imaginary axes and set two of them equal. We then find the scatter plots are reduced to narrow bands, as the mixing angles and CP phase become highly correlated and predictive. The bounds on the mixing angles and phase then become $0.45 \lsim \sin^2 θ_{23} \lsim 0.55$, $0.38 \lsim \tan^2 θ_{12} \lsim 0.50$, $0.002 \lsim \sin^2 θ_{13} \lsim 0.003$, and $60^\circ \lsim \pm δ_{CP} \lsim 85^\circ$. Moreover, successful leptogenesis and subsequent baryogenesis are also obtained, with $η_B$ increasing from $(2.7 to 6.3) \times 10^{-10}$ as $\sin^2 θ_{23}$ increases from 0.45 to 0.55.

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arXiv2004

Resonant leptogenesis in a predictive SO(10) grand unified model

An SO(10) grand unified model considered previously by the authors featuring lopsided down quark and charged lepton mass matrices is successfully predictive and requires that the lightest two right-handed Majorana neutrinons be nearly degenerate in order to obtain the LMA solar neutrino solution. Here we use this model to test its predictions for baryogenesis through resonant-enhanced leptogenesis. With the conventional type I seesaw mechanism, the best predictions for baryogenesis appear to fall a factor of three short of the observed value. However, with a proposed type III seesaw mechanism leading to three pairs of massive pseudo-Dirac neutrinos, resonant leptogenesis is decoupled from the neutrino mass and mixing issues with successful baryogenesis easily obtained.

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arXiv2004

Normal vs. Inverted Hierarchy in Type I Seesaw Models

We demonstrate that, for every grand unified model based on a conventional type I seesaw mechanism leading to a normal light neutrino mass hierarchy, one can easily generate a corresponding model with an inverted hierarchy which yields the same neutrino oscillation parameters. However, the latter type model has several unattractive instabilities which will disfavor any grand unified type I seesaw model, if an inverted neutrino mass hierarchy is observed experimentally. This should be contrasted with the softly-broken $L_e - L_μ- L_τ$ flavor symmetry models which are eliminated, if the data favors a normal mass hierarchy.

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arXiv2004

Leptogenesis in the type III seesaw mechanism

It is shown that the type III seesaw mechanism proposed recently can have certain advantages over the conventional (or type I) seesaw mechanism for leptogenesis. In particular a resonant enhancement of leptogenesis via heavy quasi-Dirac right-handed neutrino pairs can occur without a special flavor form or "texture" of the mass matrices being assumed. Some of the requirements for neutrino mixing and leptogenesis are effectively decoupled.

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arXiv2002

SO(10) GUT Models and Their Present Success in Explaining Mass and Mixing Data

Some features of SO(10) GUT models are reviewed, and a number of such models in the literature are compared. While some have been eliminated by recent neutrino data, others are presently successful in explaining the quark and lepton mass and mixing data. A short description of one very predictive model is given which illustrates some of the features discussed. Future tests of the models are pointed out including one which contrasts sharply with those models based on an $L_e - L_μ - L_τ$ type symmetry.

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arXiv2002

Lifting a Realistic SO(10) Grand Unified Model to Five Dimensions

It has been shown recently that the problem of rapid proton decay induced by dimension five operators arising from the exchange of colored Higgsinos can be simply avoided in grand unified models where a fifth spatial dimension is compactified on an orbifold. Here we demonstrate that this idea can be used to solve the Higgsino-mediated proton decay problem in any realistic SO(10) model by lifting that model to five dimensions. A particular SO(10) model that has been proposed to explain the pattern of quark and lepton masses and mixings is used as an example. The idea is to break the SO(10) down to the Pati-Salam symmetry by the orbifold boundary conditions. The entire four-dimensional SO(10) model is placed on the physical SO(10) brane except for the gauge fields, the 45 and a single 10 of Higgs fields, which are placed in the five-dimensional bulk. The structure of the Higgs superpotential can be somewhat simplified in doing so, while the Yukawa superpotential and mass matrices derived from it remain essentially unaltered.

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arXiv2002

Comparison of LMA and LOW Solar Solution Predictions in an SO(10) GUT Model

Within the framework of an SO(10) GUT model that can accommodate both the LMA and LOW solar neutrino mixing solutions by appropriate choice of the right-handed Majorana matrix elements, we present explicit predictions for the neutrino oscillation parameters Δm^2_{21}, \sin^2 2θ_{12}, \sin^2 2θ_{23}, \sin^2 2θ_{13}, and δ_{CP}. Given the observed near maximality of the atmospheric mixing, the model favors the LMA solution and predicts that δ_{CP} is small. The suitability of Neutrino Superbeams and Neutrino Factories for precision tests of the two model versions is discussed.

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