S. Dev, Sanjeev Kumar, Surender Verma, Shivani Gupta
Phenomenological implications of a class of lepton mass matrices with parallel texture structure have been examined and phenomenologically interesting constraints on charged lepton and neutrino mass matrix parameters have been obtained.
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We propose simple phenomenological lepton mass matrices which describe the three neutrinos almost degenerate in mass, leading to a very large mixing angle between $ν_μ$ and $ν_τ$, as consistent with a recent report on atmospheric neutrino oscillation from the Superkamiokande collaboration. Our matrix model also gives $ν_e-ν_μ$ mixing in agreement with the value required for neutrino oscillation to explain the solar neutrino problem.
We construct phenomenological quark-lepton mass matrices based on S$_3$ permutation symmetry in a manner fully compatible with SU(5) grand unification. The Higgs particles we need are {\bf 5}, {\bf 45} and their conjugates. The model gives a charge $-$1/3 quark vs charged lepton mass relation, and also a good fit to mass-mixing relations for the quark sector, as well as an attractive mixing pattern for the lepton sector, explaining a large mixing angle between $ν_μ$ and $ν_τ$, and either large or small $ν_e-ν_μ$ mixing angle, depending on the choice of couplings, consistent with the currently …
A phenomenological approach for the universal mass matrix model with a broken flavor 2 <-> 3 symmetry is explored by introducing the 2 <-> 3 antisymmetric parts of mass matrices for quarks and charged leptons . We present explicit texture components of the matrices, which are consistent with all the neutrino oscillation experiments and quark mixing data. The mass matrices have a common structure for quarks and leptons, while the large lepton mixings and the small quark mixings are derived with no fine tuning due to the difference of the phase factors. The model predicts a value, 2.4 x 10^{-3},…
We investigate a model that the Yukawa coupling form is constructed by two kinds of matrix (M_0 and M_1). For example, in the SO(10) GUT model, M_0 and M_1 are Yukawa couplings generated by the 10 and 126 Higgs scalars. We study how this model can give the observed mass and mixings of quarks and leptons. Parameter fitting is fully scanned by assuming all the input data to be normally distributed around the center value.
We propose a phenomenological form of the charged lepton mass matrix, which extends the idea of ``lopsided'' mass matrix in the literature. The features of the form are that both the 2-3 and 1-3 elements of the charged lepton mass matrix are of order 1 and that the small elements have a new structure . This form leads to an interesting result that both large atmospheric and solar neutrino mixing can be accounted for by the matrix. Another interesting result of this mass matrix is that it leads to very small 1-3 mixing in the lepton sector and can suppress the branching ratio of $μ\to eγ$ under…
We explore the phenomenological quark-lepton mass matrices, which are devised following the S$_3$ flavour symmetry principle, yet fully consistent with SU(5) gauge models with the Higgs particles of {\bf 5}, {\bf 45} and their conjugates. The model contains 10 free parameters altogether. When 6 parameters are fixed by charge 2/3 quark and charged lepton masses, charge($-$1/3) quark masses and all quark mixing matrix elements are predicted to be close to experiment, leaving some narrow ranges still as freedom. Further specification of 3 more parameters (using, $m_d$, Cabibbo angle and $|V_{cb}|…
We propose a model that all quark and lepton mass matrices originally have the same zero texture. Namely their (1,1), (1,3) and (3,1) components are zeros. For the neutrino mass matrix, we further impose the symmetry between the second and the third generations. Then the neutrino mass matrix has a maximal (ν_μ) - (ν_τ) mixing. Our model is consistent with all the neutrino oscillation experiments and the experimental data in the quark sector too. The neutrino mass matrix can also be well incorporated with the seesaw mechanism.
The three active light neutrinos are used to explain the neutrino oscillations. The inherently bi-large mixing neutrino mass matrix and the Fritzsch type, bi-small mixing charged lepton mass matrix are assumed. By requiring the maximal ν_μ-ν_τmixing for the atmospheric neutrino problem and the mass-squared difference approperiate for the almost maximal mixing solution to the solar neutrino problem, the following quantities are predicted: the ν_e-ν_μmixing, V_{e3}, CP violation in neutrino oscillations, and the effective electron-neutrino mass relevant to neutrinoless double beta decays.
In framework of the chiral perturbation theory we obtain the phenomenological relations between decay branches of rare radiative kaon to pion and leptons $K^+ \to π^+ l^+ l^-$ and $K^0_S \to π^0 l^+ l^-$ and meson form factors. The comparison of these results with the present day experimental data shows us that the ChPT relations for a charge kaon can determine meson form factors from already measured decay rates at high precision level. However, in the case of the neutral kaon decays $K^0 \to π^0 e^+ e^- (μ^+ μ^-)$ the formfactor data are known to a high precision than data on the differentia…
On phenomenological relations for masses and mixing parameters of quarks and leptons
本文比较分析了扩展标准模型中夸克和轻子质量与混合参数的唯象关系，发现中微子质量与混合角的新关系并证实夸克-轻子互补性，同时利用跷跷板机制估计了惰性中微子质量并探讨了大统一理论中的对称性破缺阶段。
By using a model independent Monte Carlo approach, we study the possible structure of charged and neutral lepton mass matrices, under the assumption of an U(2) horizontal symmetry (additional to the usual Standard Model ones) involving the light fermion generations. We assume the most general Majorana mass matrix for neutrinos. We update the results of our previous similar study, by inserting in the analysis the recent KamLAND data, that contributed to find a final solution to the Solar neutrino problem. The introduction of the new experimental data reduce the allowed regions in the nine dimen…
CP and T asymmetries in neutrino oscillations, in vacuum as well as in matter, are expressed in terms of invariant functions of lepton mass matrices.
In view of the precise measurement of the leptonic mixing angle θ_{13}, implications of the latest mixing data have been investigated for lepton mass matrices pertaining to Dirac neutrinos.These texture specific lepton mass matrices have been examined for their compatibility with the latest data in the cases of normal hierarchy, inverted hierarchy and degenerate scenario of neutrino masses.
We reanalyze the mass matrix model of quarks and leptons that gives a unified description of quark and lepton mass matrices with the same texture form. By investigating possible types of assignment for the texture components of the lepton mass matrix, we find that a different assignment for neutrinos than for charged leptons can also lead to consistent values of the MNSP lepton mixing matrix. We also find that the predicted value for the lepton mixing matrix element $U_{13}$ of the model depends on the assignment. A proper assignment will be discriminated by future experimental data for $U_{13…
We construct new invariants and give several theorems which determine in general (i) the number of physically meaningful phases in charged lepton and neutrino mass matrices and (ii) which elements of these matrices can be rendered real by rephasings. We illustrate our results with simple models.
In an attempt at explaining the observed neutrino mass-squared differences and leptonic mixing, lepton mass matrices with zero textures have been widely studied. In the weak basis where the charged lepton mass matrix is diagonal, various neutrino mass matrices with two zeros have been shown to be consistent with the current experimental data. Using the canonical and Smith normal form methods, we construct the minimal Abelian symmetry realizations of these phenomenological two-zero neutrino textures. The implementation of these symmetries in the context of the seesaw mechanism for Majorana neut…
We discuss complex rephasing invariants of charged lepton and neutrino mass matrices and associated theorems which determine in general (i) the number of physically meaningful phases in these matrices and (ii) which elements of these matrices can be rendered real by rephasings. New results are presented on higher order complex invariants and the application of the methods to several models.
The universality hypothesis for quark and lepton mixing matrices (CKM and MNS) is further developed. This hypothesis explains why the CKM is almost diagonal whereas the MNS is almost maximally mixed. If this hypothesis is true, the Dirac CP violating phase of the MNS mixing matrix is bounded around $π$ or 0. Quark-lepton mass matrices which realizes this hypothesis are constructed, showing simple power law relations among mass matrices for up-type, down-type quarks and neutrinos.
It has been suggested that residual symmetries in the charged-lepton and neutrino mass matrices can possibly reveal the flavour symmetry group of the lepton sector. We review the basic ideas of this purely group-theoretical approach and discuss some of its results. Finally, we also list its shortcomings.
My talk is concentrating on the quantum effects on neutrino mass and lepton flavor mixing matrices in the framework of the minimal supersymmetric standard model with the effective dimension-five operator which gives the Majorana masses of neutrinos.
By using the anomalous magnetic and electric dipole moments of the $τ$ lepton in an effective lagrangian approach to the new physics, we investigate the lepton flavor violation (LFV) decays, $l\to l'γ$, and $μ,τ$ anomalous magnetic and electric dipole moments in a lepton mass matrices ansatz which induced by SUSY GUT. We put very stringent constraints LFV decays and $τ$ anomalous magnetic and electric dipole moments.
We assume that all quark and lepton $3 \times 3$ mass matrices which appear in the standard model lagrangian (after spontaneous symmetry breaking) with neutrinos treated as Dirac patricles have the triangular form. Such matrices have not only less non-zero elements (three of them are equal to zero) but also lead to very asymmetrical decomposition into one diagonal and two unitary matrices for quarks and leptons. We also assume that unitary matrices which transform flavor into definite mass states for right handed components (weakly non-interacting) in the same weak isodoublet are equal. Using …
Several phenomenological features of fermion masses and mixings can be accounted for by a simple model for fermion mass matrices, which suggests an underlying U(2) horizontal symmetry. In this context, it is also proposed how an approximate quark-lepton symmetry can be achieved without unified gauge theories.
Against the conventional picture that the mass matrix forms in the quark sectors will take somewhat different structures from those in the lepton sectors, on the basis of an idea that all the mass matrices of quarks and leptons have the same texture, a universal texture of quark and lepton mass matrices is proposed by assuming a discrete symmetry Z_3 and an extended flavor 2\leftrightarrow 3 symmetry. The texture is described by three parameters (including phase parameter). According to this ansatz, the neutrino masses and mixings are investigated.
The quark-lepton complementarity (QLC) is very suggestive in understanding possible relations between quark and lepton mixing matrices. We explore the QLC relations in all the possible angle-phase parametrizations and point out that they can approximately hold in five parametrizations. Furthermore, the vanishing of the smallest mixing angles in the CKM and PMNS matrices can make sure that the QLC relations exactly hold in those five parametrizations. Finally, the sensitivity of the QLC relations to radiative corrections is also discussed.
To search for possible textures of lepton mass matrices, we systematically examine flavor mixing structures which can lead to large lepton mixing angles. We find out 37 mixing patterns are consistent with experimental data, taking into account phase factors in the mixing matrices. Only six of the patterns can explain the observed data without any tuning of parameters, while the others need particular choices for the phase values. It is found that these six mixing patterns are those predicted by the models which have been proposed to account for fermion mass hierarchies. On the other hand, the …
The permutation symmetry $S_3$ is appplied to obtain two equal Majorana neutrino masses, while maintaining three different charged-lepton masses and suppressing neutrinoless double beta decay. The resulting radiative splitting of the two neutrinos is shown to be suitable for solar neutrino vacuum oscillations.
An analysis of the leptonic texture for the new triangular mass matrices has been carried out. In particular, it is shown that both bimaximal and nearly bimaximal solutions for solar and atmospheric neutrino anomalies can be generated within this pattern. We have also derived exact and compact parametrization of the leptonic mixing matrix in terms of the lepton masses and the parameters $α, β'$ and $δ$. A consistency with the CHOOZ reactor result for $V_m{_{13}}$ and a smallness of the Jarlskog's invariant parameter are obtained.
In the so-called yukawaon model, where effective Yukawa coupling constants Y_f^{eff} (f=e,ν,u,d) are given by vacuum expectation values of gauge singlet scalars (yukawaons) Y_f with 3\times 3 flavor components, it is tried to give a unified description of quark and lepton mass matrices. Especially, without assuming any discrete symmetry in the lepton sector, nearly tribimaximal mixing is derived by assumed a simple up-quark mass matrix form.
There are many viable combinations of texture zeros in lepton mass matrices. We propose an economical and stable mass texture. Analytical and numerical results on mixing parameters and the effective mass of neutrinos are obtained. These results satisfy new constraints from neutrinos oscillation experiments and cosmological observations. Our proposition reveals that in the complex forest of neutrinos mixing models, a simple and robust one is still possible.
We propose a model that all quark and lepton mass matrices have the same zero texture. Namely their (1,1), (1,3) and (3,1) components are zeros. The mass matrices are classified into two types I and II. Type I is consistent with the experimental data in quark sector. For lepton sector, if seesaw mechanism is not used, Type II allows a large $ν_μ- ν_τ$ mixing angle. However, severe compatibility with all neutrino oscillation experiments forces us to use the seesaw mechanism. If we adopt the seesaw mechanism, it turns out that Type I instead of II can be consistent with experimental data in the …
We show that there exist six parallel textures of the charged lepton and neutrino mass matrices with six vanishing entries, whose phenomenological consequences are exactly the same. These {\it isomeric} lepton mass matrices are compatible with current experimental data at the $3σ$ level. If the seesaw mechanism and the Fukugita-Tanimoto-Yanagida hypothesis are taken into account, it will be possible to fit the experimental data at or below the $2σ$ level. In particular, the maximal atmospheric neutrino mixing can be reconciled with a strong neutrino mass hierarchy in the seesaw case.
We reanalyze the mass matrices model of quarks and leptons which gives a unified description of quark and lepton mass matrices with the same texture form. By investigating possible types of the assignment for the texture's components of this mass matrix form, we find that a different assignment for up-quarks from one for down-quarks can lead to consistent values of CKM mixing matrix. This finding overcomes a weak point of the previous analysis of the model. We also obtain some relations among the CKM mixing matrix parameters, which are independent of evolution effects.
Based on a supersymmetric Yukawaon model with O(3) family symmetry, possible forms of quark and lepton mixing matrices are systematically investigated under a condition that the up-quark mass matrix form leads to the observed nearly tribimaximal mixing in the lepton sector. Although the previous model could not provide a good fitting of the observed quark mixing, the present model can give a reasonably good fitting not for lepton mixing but also the quark mixing by using a different origin of the $CP$ violation from one in the previous model.
Several popular Ansätze of lepton mass matrices that contain texture zeros are confronted with current neutrino observational data. We perform a systematic $χ^2$-analysis in a wide class of schemes, considering arbitrary Hermitian charged lepton mass matrices and symmetric mass matrices for Majorana neutrinos or Hermitian mass matrices for Dirac neutrinos. Our study reveals that several patterns are still consistent with all the observations at 68.27% confidence level, while some others are disfavored or excluded by the experimental data. The well-known Frampton-Glashow-Marfatia two-zero textu…
We study a flavor model that the quark sector has the $S_3$ modular symmetry,while the lepton sector has the $A_4$ modular symmetry. Our model leads to characteristic quark mass matrices which are consistent with experimental data of quark masses, mixing angles and the CP violating phase. The lepton sector is also consistent with the experimental data of neutrino oscillations. We also study baryon and lepton number violations in our flavor model.
Implications of the lepton mixing angles, in particular of theta_13, have been investigated for minimal as well as non-minimal Fritzsch-like textures for the case of Majorana neutrinos. Both, in minimal texture (texture 6 zero lepton mass matrices) and non-minimal textures (two cases of texture 5 zero lepton mass matrices), inverted hierarchy and degenerate scenario of neutrino masses have been ruled out. The implications of theta_13 have been investigated on the lightest neutrino mass m_ν_1 as well as the effective Majorana mass m_ee.
The generic predictions of two-texture zero neutrino mass matrices of class A in the flavor basis have been reexamined especially in relation to the degeneracy between mass matrices of types A_1 and A_2 and interesting constraints on the neutrino parameters have been obtained. It is shown that the octant of $θ_{23}$ and the quadrant of the Dirac-type CP-violating phase $δ$ can be used to lift this degeneracy.
We study predictive textures for the lepton mass matrices in which the charged-lepton mass matrix has either four or five zero matrix elements while the neutrino Majorana mass matrix has, respectively, either four or three zero matrix elements. We find that all the viable textures of these two kinds share many predictions: the neutrino mass spectrum is inverted, the sum of the light-neutrino masses is close to 0.1 eV, the Dirac phase $δ$ in the lepton mixing matrix is close to either $0$ or $π$, and the mass term responsible for neutrinoless double-beta decay lies in between 12 and 22 meV.
The phenomenological model that all quark and lepton mass matrices have the same zero texture, namely their (1,1), (1,3) and (3,1) components are zeros, is discussed in the context of SO(10) Grand Unified Theories (GUTs). The mass matrices of type I for quarks are consistent with the experimental data in the quark sector. For the lepton sector, consistent fitting to the data of neutrino oscillation experiments force us to use the mass matrix for the charged leptons which is slightly deviated from type I. Given quark masses and charged lepton masses, the model includes 19 free parameters, where…
Recently, we proposed a unified mass matrix model for quarks and leptons, in which, mass ratios and mixings of the quarks and neutrinos are described by using only the observed charged lepton mass values as family-number-dependent parameters and only six family-number-independent free parameters. In spite of quite few parameters, the model gives remarkable agreement with observed data (i.e. CKM mixing, PMNS mixing and mass ratios). Taking this phenomenological success seriously, we give a formulation of the so-called Yukawaon model in details from a theoretical aspect, especially for the const…
We study the implications of having a similarity between quark and lepton mixing in the Dirac sector of the Standard Model plus the right-handed neutrino. This enable us to describe all masses and mixings in the Dirac sector in terms of only five parameters: three mass scales $m_b$, $m_τ$ and $m_t$, one parameter $λ$ describing all the mixings, and a CP violating phase in the quark sector. Then, from experimental data on neutrino masses and mixings, we extract the heavy neutrino mass matrix. The approach considered, although does not contraddict Grand Unified Theories, can help to find other t…
Taking into account the latest neutrino oscillation data, we study texture zeros of the lepton mass matrices. Assuming the Dirac neutrino mass matrix M_D, the charged-lepton mass matrix M_l and the mass matrix of heavy right-handed Majorana neutrinos M_R to have three texture zeros, we show that the observed neutrino mixing angles can naturally be obtained. The phenomenological implications for the neutrino mass spectrum, the CP-violating phases, the tritium beta decay and the neutrinoless double-beta decay are explored.
In the simplest model of horizontal U(1) symmetry with one singlet added to the supersymmetric standard model, we systematically reconstruct quark mass matrices from the low-energy data to prove that there are only two mass matrices found by Binetruy et.~al.. The same U(1) symmetry constrains the hierarchical structure of L-violating couplings, from which we build radiative neutrino mass matrices accommodating the solar and hot dark matter neutrino masses and mixing. We find a few patterns of acceptable charged lepton and neutrino mass matrices, most of which are consistent with large $\tanβ\s…
The one-loop renormalization-group equations (RGEs) running behavior of quark and lepton mass matrices with general structures are studied simultaneously. Suppose the non-linear terms of RGEs are dominated by the Yukawa couplings of top quark and τ lepton, the unitary matrices that diagonalize the mass matrices of up-type quark and charged lepton in Hermitian basis are found as invariant with energy scale. Based on this result, we can decouple the RGEs and obtain the RGE corrected mass matrices of fermion. As examples, we consider the renormalization-group evolution of fermion matrices with fo…
We propose two ans$\rm\ddot{a}$tze of lepton mass matrices with four texture zeros, and confront them with current experimental data on neutrino oscillations. The parameter space of each ansatz is carefully explored. We find that both ans$\rm\ddot{a}$tze can accommodate the normal hierarchy of neutrino masses and the bi-large pattern of lepton flavor mixing. Their predictions for the effective mass of the tritium beta decay and that of the neutrinoless double beta decay are too small to be detectable, but leptonic CP violation at the percent level is allowed. Some discussions are also given ab…
We study a variety of different texture patterns in the basis in which the charged lepton mass matrix or neutrino mass matrix or neither are diagonal. The experimental results on the neutrinos provide sufficient restrictions to allow only a small number of simple patterns. We discuss particularly the texture zeroes which provide important relations among the mass eigenvalues and the mixing matrix.
A new ansatz for quark and lepton mass matrices is proposed in the context of supersymmetric grand unified theories. The 13 parameters describing fermion masses and mixings are determined in terms of only 6 free parameters, allowing 7 testable predictions. The values of $V_{us}$, $V_{cb}$, $V_{ub}$, $m_u$, $m_d$, $m_s$, and $m_b$ are then predicted as a function of the 3 charged lepton masses, $m_c$, $m_t$, and $\tan β$, the ratio of Higgs vacuum expectation values. In particular the Cabibbo angle and $m_s/m_d$ are determined in terms of only lepton masses. All predictions are in very good agr…
Realistic quark masses and mixing angles are obtained applying the successful $A_4$ family symmetry for leptons, motivated by the quark-lepton assignments of SU(5). The $A_4$ symmetry is suitable to give tri-bimaximal neutrino mixing matrix which is consistent with current experimental data. We study new scenario for the quark sector with the $A_4$ symmetry.
Rephasing invariants of quark and lepton mixing matrices are obtained in the standard model extended by the seesaw mechanism, and in its low-energy effective theory with the dimension-five Majorana mass operator. We classify the basic invariants, discuss non-trivial relations between them, and determine the independent invariants which characterize all the information in the mixing matrices in a basis-independent way. We also discuss the restrictions on the allowed ranges for the mixing phases, and on the rephasing invariants, which follow from a discrete invariance of the Majorana mass matrix…
As an attempt to give an unified description of quark and lepton mass matrices M_f, the following mass matrix form is proposed: the form of the mass matrices are invariant under a cyclic permutation (f_1 \to f_2, f_2 \to f_3, f_3 \to f_1) among the fermions f_i. The model naturally leads to the maximal mixing between ν_μand ν_τ, and with an additional ansatz, it leads to the well-satisfied relations |V_{us}| \simeq \sqrt{m_d/m_s} and |V_{cb}| \simeq \sqrt{m_d/m_b}.
By introducing a set of new triplet leptons (with nonzero hypercharge) that can Yukawa couple to their Standard Model counterparts, new sources of tree-level flavor changing currents are induced via mixing. In this work, we study some of the consequences of such new contributions on processes such as the leptonic decays of gauge bosons, $\ell \rightarrow 3\ell'$ and $\ell \rightarrow \ell' γ$ which violate lepton flavor, and mu-e conversion in atomic nuclei. Constraints are then placed on the parameters associated with the exotic triplets by invoking the current low-energy experimental data. M…
We present a detailed study on triminimal parametrizations of quark and lepton mixing matrices with different basis matrices. We start with a general discussion on the triminimal expansion of the mixing matrix and on possible unified quark and lepton parametrization using quark-lepton complementarity (QLC). We then consider several interesting basis matrices and compare the triminimal parametrizations with the Wolfenstein-like parametrizations. The usual Wolfenstein parametrization for quark mixing is a triminimal expansion around the unit matrix as the basis. The corresponding QLC lepton mixi…
We investigate the texture structures of lepton mass matrices with four (five) non-zero elements in the charged lepton mass matrix and three (four) vanishing cofactors in the neutrino mass matrix. Using weak basis transformations, all possible textures for three and four vanishing cofactors in $M_ν$ are grouped into 7 classes and predictions for the unknown parameters such as the Dirac CP violating phase and the effective Majorana mass for the phenomenologically allowed textures have been obtained. We, also, illustrate how such texture structures can be realized using discrete Abelian flavor s…
We propose a mass matrix model that gives a unified description of quark and lepton with the same texture form based on a flavor 2 <-> 3 symmetry. The model is in contrast with the conventional picture that the mass matrix forms in the quark sector will take somewhat different structures from those in the lepton sector. By investigating possible types of assignment for masses, we find that our quark mass matrices can lead to small CKM quark mixings which are consistent with experimental values. We also find some phase-parameter-independent relations among CKM quark mixing matrix elements.
We discuss conditions under which bi-large mixing in the lepton sector is achieved assuming that all Yukawa matrices and the right-handed neutrino mass matrix have the same singular form in the leading order. Due to obvious quark lepton symmetry, this approach can be embedded into grand unified theories. The right-handed neutrino mass scale can be identified with the GUT scale and, as a consequence of third generation Yukawa coupling unification, the mass of the lightest neutrino is given as (m_{top}^2/M_{GUT})|U_{τ1}|^2 in the leading order. This relation does not depend on the exact form of …
We analyze the lepton sector of a recently proposed nonsymmetric mass matrix model. Our model gives a unified description of quark and lepton with the same texture form based on an extended flavor $2 \leftrightarrow 3$ symmetry with a phase. By investigating possible types of assignment for masses, we find that the model can lead to large lepton mixings which are consistent with experimental values. We also find that the model predicts a very small value, $1.3\times10^{-10}$, for the lepton mixing matrix element square $|U_{13}|^2$. The CP violating phases in the lepton mixing matrix and a sup…
We propose a simple ansatz for neutrino phenomenology, in which the relevant lepton mass matrices take the universal Fritzsch-like form and the seesaw relation holds under a particular condition. There exist six textures of this nature, but their consequences on neutrino oscillations are exactly the same. We show that our scenario is viable to account for the cosmological baryon number asymmetry via thermal leptogenesis. Its predictions for the lepton-flavor-violating decays μ-> eγ, tau -> μγand τ-> eγare also presented. We find that the branching ratios of these rare processes depend strongly…
Neutrino oscillation experiments (excluding the LSND experiment) suggest a tri-bimaximal form for the lepton mixing matrix. This form indicates that the mixing matrix is probably independent of the lepton masses, and suggests the action of an underlying discrete family symmetry. Using these hints, we conjecture that the contrasting forms of the quark and lepton mixing matrices may both be generated by such a discrete family symmetry. This idea is that the diagonalisation matrices out of which the physical mixing matrices are composed have large mixing angles, which cancel out due to a symmetry…
We show that the Fritzsch texture of lepton mass matrices can naturally lead to the bi-large flavor mixing pattern, if three neutrinos have a normal but weak mass hierarchy (typically, $m_1 : m_2 : m_3 \sim 1 : 3 :10$). The effective mass of the tritium beta decay and that of the neutrinoless double beta decay are too small to be observable in this ansatz, but CP violation at the percent level is allowed and could be measured in long-baseline neutrino oscillations.
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