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Ernest Ma

Publications and source records attributed to Ernest Ma.

At least 217 records · Page 12Linked to original sources
arXiv2005

Neutrino Mass Matrix from S_4 Symmetry

The cubic symmetry S_4 contains A_4 and S_3, both of which have been used to study neutrino mass matrices. Using S_4 as the family symmetry of a complete supersymmetric theory of leptons, it is shown how the requirement of breaking S_4 at the seesaw scale without breaking supersymmetry enforces a special form of the neutrino mass matrix which exhibits maximal nu_mu - nu_tau mixing as well as zero U_e3. In addition, (nu_e + nu_mu + nu_tau)/sqrt{3} is naturally close to being a mass eignestate, thus predicting tan^2 theta_12 to be near but not equal to 1/2.

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arXiv2005

Efficacious Additions to the Standard Model

If split supersymmetry can be advocated as a means to have gauge-coupling unification as well as dark matter, another plausible scenario is to enlarge judiciously the particle content of the Standard Model to achieve the same goals without supersymmetry. A simple efficacious example is presented.

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arXiv2005

Tetrahedral Family Symmetry and the Neutrino Mixing Matrix

In a new application of the discrete non-Abelian symmetry A_4 using the canonical seesaw mechanism, a three-parameter form of the neutrino mass matrix is derived. It predicts the following mixing angles for neutrino oscillations: theta_{13}=0, sin^2 theta_{23}=1/2, and sin^2 theta_{12} close, but not exactly equal to 1/3, in one natural symmetry limit.

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arXiv2005

Hybrid Seesaw Neutrino Masses with A_4 Family Symmetry

We consider the scenario in which neutrino data are explained by the interplay of type I and II seesaw terms in the Majorana neutrino mass matrix ${\cal M}_ν= {\cal M}_L - {\cal M}_D {\cal M}_R^{-1} {\cal M}_D^T$. We construct a predictive model with ${\cal M}_L$ proportional to the unit matrix, 3 diagonal texture zeros in ${\cal M}_R$, and ${\cal M}_D$ diagonal. We show how this pattern can be maintained by the non-Abelian discrete symmetry $A_4$, and discuss its phenomenological consequences. It turns out that the two types of seesaw give contributions of the same order to ${\cal M}_ν$. In the CP conserving case, we find $\sinθ_{13}\approx 2/(\tan 2θ_{23} \tan 2θ_{12})$ and we predict inverted (normal) ordering of the mass spectrum for $\tan^2θ_{12} < 0.5 ~(>0.5)$.

hep-ph↗
arXiv2005

Predicting Neutrinoless Double Beta Decay

We give predictions for the neutrinoless double beta decay rate in a simple variant of the A_4 family symmetry model. We show that there is a lower bound for the neutrinoless double beta decay amplitude even in the case of normal hierarchical neutrino masses, corresponding to an effective mass parameter |m_{ee}| >= 0.17 \sqrt{Δm^2_{ATM}}. This result holds both for the CP conserving and CP violating cases. In the latter case we show explicitly that the lower bound on |m_{ee}| is sensitive to the value of the Majorana phase. We conclude therefore that in our scheme, neutrinoless double beta decay may be accessible to the next generation of high sensitivity experiments.

hep-ph↗
arXiv2005

Hiding the Existence of a Family Symmetry in the Standard Model

If a family symmetry exists for the quarks and leptons, the Higgs sector is expected to be enlarged to be able to support the transformation properties of this symmetry. There are however three possible generic ways (at tree level) of hiding this symmetry in the context of the Standard Model with just one Higgs doublet. All three mechanisms have their natural realizations in the unification symmetry E_6 and one in SO(10). An interesting example based on SO(10) X A_4 for the neutrino mass matrix is discussed.

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arXiv2005

Aspects of the Tetrahedral Neutrino Mass Matrix

The four-parameter tetrahedral neutrino mass matrix introduced earlier by the author is studied in two specific limits, both having only two parameters and resulting in theta_13=0, theta_23=pi/4, and tan^2 theta_12=1/2. One limit corresponds to a recent proposal which predicts a normal ordering of neutrino masses; the other is new and allows both inverted and normal ordering.

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arXiv2005

Discrete Symmetry and CP Phase of the Quark Mixing Matrix

A simple specific pattern of the two 3 X 3 quark mass matrices is proposed, resulting in a prediction of the CP phase of the charged-current mixing matrix V_CKM, i.e. sin 2 phi_1 (beta) = 0.733, which is in remarkable agreement with data, i.e. sin 2 phi_1 = 0.728 +/- 0.056 +/- 0.023 from Belle and sin 2 beta = 0.722 +/- 0.040 +/- 0.023 from Babar. This pattern can be maintained by a discrete family symmetry, an example of which is D_7, the symmetry group of the heptagon.

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arXiv2005

Smallness of Leptonic $θ_{13}$ and Discrete Symmetry

The leptonic mixing angle $θ_{13}$ is known to be small. If it is indeed tiny, the simplest explanation is that charged leptons mix only in the $μ-τ$ sector and neutrinos only in the 1-2 sector. We show that this pattern may be explained by the discrete symmetry $Z_2 \times Z_2$ of a complete Lagrangian, which has 2 Higgs doublets and 2 Higgs triplets (or 2 heavy right-handed singlet neutrinos). In the case of Higgs triplets, the Majorana neutrino masses are arbitrary, whereas in the case of heavy singlet neutrinos, an inverted hierarchy is predicted. Lepton-Flavor-Violation effects, present only in the $μ-τ$ sector, are analyzed in detail: the LFV $τ$-decay rates are predicted below the present bounds by a few orders of magnitude, whereas LFV Higgs decays could allow for a direct test of the model.

hep-ph↗
arXiv2005

Two predictive supersymmetric S3 x Z2 models for the quark mass matrices

We propose two simple models for the quark mass matrices which may be implemented through an S3 x Z2 symmetry in a supersymmetric context. Each model has eight parameters and, therefore, makes two independent predictions for the quark mixing matrix. The first model predicts |Vub / Vcb| approx sqrt{m_u / m_c} sim 0.06 and |Vtd / Vts| approx sqrt{m_d / m_s} sim 0.23. The second model, in which the forms of the up-type-quark and down-type-quark mass matrices are interchanged relative to the first one, predicts |Vub / Vcb| sim 0.11 and |Vtd / Vts| sim 0.33. Both models have sin(2 beta) sim 0.5.

hep-ph↗
arXiv2005

Triplicity of Quarks and Leptons

Quarks come in three colors and have electric charges in multiples of one-third. There are also three families of quarks and leptons. Whereas the first two properties can be understood in terms of unification symmetries such as SU(5), SO(10), or E_6, why there should only be three families remains a mystery. I propose how all three properties involving the number three are connected in a fivefold application of the gauge symmetry SU(3).

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arXiv2004

Grand Unification and Physics Beyond the Standard Model

Recent progress in some selected areas of grand unification and physics beyond the standard model is reviewed. Topics include gauge coupling unification, SU(5), SO(10), symmetry breaking mechanisms, finite field theory: SU(3)^3, leptonic color: SU(3)^4, chiral color and quark-lepton nonuniversality: SU(3)^6.

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arXiv2004

Polygonal Derivation of the Neutrino Mass Matrix

Representations of the symmetry group D_n of the n-sided regular polygon have generic multiplication rules if n is prime. Using D_n with n=5 or greater, a particular well-known form of the Majorana neutrino mass matrix is derived.

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arXiv2004

Quaternion Family Symmetry of Quarks and Leptons

To a first approximation, the quark mixing matrix has $θ^q_{13} = θ^q_{23} = 0$, whereas the lepton mixing matrix has $θ^l_{23} = π/4$. We show how this structure may be understood if the family symmetry is $Q_8$, the quaternion group of eight elements. We find three viable scenarios for the Majorana neutrino mass matrix, each depending on 4 parameters and predicting a specific mass spectrum. The phenomenology of the two Higgs doublets which generate the Yukawa sector is analyzed and testable predictions are derived. We discuss also the closely related model based on $D_4$, the symmetry group of the square.

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