We explore masses and mixings for Dirac neutrinos in models where lepton number is conserved, under the guidance of a hidden, but broken, $μ-τ$ exchange symmetry, that makes itself evident in the squared hermitian mass matrix. We study the parameter space in the most general theory as allowed by current neutrino oscillation experiment data. By using a general parameterization of the mass matrix which contains only observable parameters we stablish that the amount of breaking of the symmetry is in the range of the atmospheric mass scale, without regard to the neutrino hierarchy, the absolute neutrino mass and the Dirac CP phase. An estimate of the invisible branching ratio for a Higgs boson decaying into Dirac neutrinos, $H\rightarrowν\overlineν$ , is given and compared to recent measurements in this context.
If neutrinos are Dirac, the conditions for cobimaximal mixing, i.e. $θ_{23}=π/4$ and $δ_{CP}=\pm π/2$ in the $3 \times 3$ neutrino mixing matrix, are derived. One example with $A_4$ symmetry and radiative Dirac neutrino masses is presented.
Implications of recently measured leptonic mixing angle $θ_{13}$ as well as the other two mixing angles have been examined for Fritzsch-like mass matrices with minimal texture for Dirac neutrinos. Interestingly, the existing data seems to rule out this texture specific case of Dirac neutrinos for normal, inverted hierarchy as well as degenerate scenario of masses.
We explore the consequences of the neutrino mass matrix having a hidden $\mathcal{Z}_2$ symmetry and one zero eigenvalue. When implemented, these two conditions give relations among the mixing angles. In addition, fitting these relations to the existing oscillation data allows limits to be placed on the parameter of the symmetry.
We present a model which employs the seesaw mechanism with five right-handed neutrinos, leading to trimaximal and CP-conserving lepton mixing. Tri-bimaximal mixing is a natural limiting case of our model which occurs when one particular vacuum expectation value is real and preserves the mu-tau interchange symmetry of the Lagrangian. Our model allows for leptogenesis even in the case of exact tri-bimaximal mixing.
We introduce a new parametrization of the MNS lepton mixing matrix which separates the hierarchical Grand Unified relations among quarks and leptons. We argue that one large angle stems from the charged leptons, the other from the seesaw structure of the neutral lepton mass matrix. We show how two large mixing angles can arise naturally provided there are special requirements on the Dirac ($ΔI_{\rm w}=1/2$) and Majorana ($ΔI_{\rm w}=0$) masses. One possibility is a correlated hierarchy between them, the other is that the $ΔI_{\rm w}=0$ Majorana mass has a specific texture; it is Dirac-like for…
Choosing how gauge $U(1)_χ$ breaks in the context of $SO(10) \to SU(5) \times U(1)_χ$, $Z_4$ lepton number may be obtained which maintains neutrinos as Dirac fermions. Choosing $Δ(27)$ as the family symmetry of leptons, tree-level Dirac neutrino masses may be forbidden. Choosing a specific set of self-interacting dark-matter particles, Dirac neutrino masses and mixing may then be generated in two loops. This framework allows the realization of cobimaximal neutrino mixing, i.e. $θ_{13} \neq 0$, $θ_{23} = π/4$, $δ_{CP} = \pm π/2$, as well as the desirable feature that the light scalar mediator o…
Using discrete flavour group, $A_5$, combined with generalised CP, we study the mixing parameter correlations which arise from breaking to residual symmetries in the neutrino, $G_ν=\mathbb{Z}_2\times \text{CP}$, and charged lepton sectors, $G_{e}=\mathbb{Z}_2$. By focusing on patterns that agree with current experimental data we demonstrate that non-trivial leptonic phases are predicted and discuss a number of distinctive correlations between mixing parameters.
We present some considerations in connection with the paper arXiv:1004.2980 [hep-ph] and give a response to the criticism of the quasipotential approach in our relativistic quark model.
To generate the minimal neutrino Majorana mass matrix that has a free solar mixing angle and Delta m_sol^2 = 0 it suffices to implement an O(2) symmetry, or one of its subgroups SO(2), Z_N (N>2), or D_N (N>2). This O(2) generalizes the hidden Z_2^s of lepton mixing and leads in addition automatically to mu-tau symmetry. Flavor-democratic perturbations, as expected e.g. from the Planck scale, then result in tri-bimaximal mixing. We present a minimal model with three Higgs doublets implementing a type-I seesaw mechanism with a spontaneous breakdown of the symmetry, leading to large theta_13 and …
We argue how pseudo-Dirac scenario for neutrinos leads to rich neutrino oscillation phenomena, including oscillation inside each generation. The pseudo-Dirac scenario is generalized by incorporating generation mixings and formulae for the various neutrino oscillations are derived. As the application we compare the formulae with the corresponding data. We find that observed pattern of mixings, such as almost maximal mixing in the atmospheric neutrino oscillation, is naturally explained in the generalized Pseudo-Dirac scenario with small generation mixings. We, however, also point out that there…
We propose a realization of the so-called bimodal/schizophrenic model proposed recently. We assume S4, the permutation group of four objects as flavor symmetry giving tri-bimaximal lepton mixing at leading order. In these models the second massive neutrino state is assumed quasi-Dirac and the remaining neutrinos are Majorana states. In the case of inverse mass hierarchy, the lower bound on the neutrinoless double beta decay parameter m_ee is about two times that of the usual lower bound, within the range of sensitivity of the next generation of experiments.
We present predictions for CP violating phases of the Type-I seesaw model with four-zero textures on the Dirac mass matrix. For the four-zero textures, the effective low energy Majorana mass matrix is parametrized with seven parameters. They are three mass-dimensional parameters, two angles and two CP violating sources. The number of these parameters is less than that of the general description of the Majorana mass matrix with three neutrino masses, three mixing angles and three CP violating phases. In particular, only two independent CP violating sources give rise to three CP violating phases…
We consider a minimal condition that predicts the 1-3 lepton mixing angle $θ_{13} \simeq θ_{\rm C}/\sqrt{2}$ with $θ_{\rm C}$ the Cabibbo angle, and give the improved prediction of $θ_{13}$. In the case of normal mass ordering, the theoretical value of $θ_{13}$ is predicted as $θ_{13}=8.6^\circ$, which is in good agreement with the current global best fit. In the case of inverted mass ordering, the theoretical value is predicted as $θ_{13}=9.7^\circ$, which is far from the current global best fit. We also study the leptonic CP violation. We show that any values of the leptonic Dirac CP phase $…
We present a model-independent analysis of Leptonic CP violation for some well known mixing scenarios. In particular, we considered modified schemes for Bimaximal(BM), Democratic(DC), Hexagonal(HG) and Tribimaixmal(TBM) mixing for our numerical investigation. These model-independent corrections to mixing matrices are parameterized in terms of complex rotation matrices ($U$) with related modified PMNS matrix of the forms \big($U_{ij}^l\cdot V_{M},~V_{M}\cdot U_{ij}^r$ \big ) where $U_{ij}^{l, r}$ is complex rotation in ij sector and $V_{M}$ is unperturbed mixing scheme. We present generic formu…
Experimental results indicate a possible relation between the lepton and quark mixing matrices of the form U_PMNS \approx V_CKM^\dagger U_X, where U_X is a matrix with special structure related to the mechanism of neutrino mass generation. We propose a framework which can realize such a relation. The main ingredients of the framework are the double seesaw mechanism, SO(10) Grand Unification and a hidden sector of theory. The latter is composed of singlets (fermions and bosons) of the GUT symmetry with masses between the GUT and Planck scale. The interactions in this sector obey certain symmetr…
We discuss the energy scale profile of the bi-maximal mixing which is given at the GUT energy scale in the minimal SUSY model, associated with an assumption that Y_nu^dagger Y_nu is diagonal, where Y_nu is the neutrino-Yukawa coupling matrix. In this model, the Dirac mass matrix which appears in the seesaw neutrino mass matrix is determined by three neutrino masses, two relative Majorana phases and three heavy Majorana masses. All CP phases are related by two Majorana phases. We show that the requirement that the solar mixing angle moves from the maximal mixing at GUT to the observed one as th…
We study the implications of neutrino oscillations with maximal mixing for the neutrino Dirac and Majorana matrices in the see-saw mechanism for three non degenerate neutrino masses. We find the form of the Dirac matrix for a structure-less Majorana matrix and, conversely, the structure of the Majorana matrix if the Dirac matrix is according to our naive intuition. We give some examples of Majorana matrices that, in a 3 X 3 context, lead to maximal mixing without too much fine tuning and cross talk with the Dirac input.
There are good reasons why neutrinos could be Majorana particles, but there exist also a number of very good reasons why neutrinos could have Dirac masses. The latter option deserves more attention and we derive therefore analytic expressions describing the renormalization group evolution of mixing angles and of the CP phase for Dirac neutrinos. Radiative corrections to leptonic mixings are in this case enhanced compared to the quark mixings because the hierarchy of neutrino masses is milder and because the mixing angles are larger. The renormalization group effects are compared to the precisi…
An analysis is given of the Stueckelberg extension of the Standard Model with a hidden sector gauge group $U(1)_X$ where the mass growth for the extra gauge boson occurs via the Stueckelberg mechanism, and where the kinetic mixing in the $U(1)_X\times U(1)_Y$ sector is included. Such a kinetic mixing is generic in a broad class of supergravity and string models. We carry out a detailed global fit of the model with the precision LEP data on and off the $Z$ pole, with $χ^2$ within 1% of the $χ^2$ of the Standard Model fit. Further, it is shown that in the absence of matter in the hidden sector, …
In this paper, we derive in a novel approach the possible textures of neutrino mass matrix that can lead us to maximal atmospheric mixing angle and Dirac CP phase which are consistent with the current neutrino oscillation data. A total of eleven textures are thus found. Interestingly, the specific texture given by the $μ$-$τ$ reflection symmetry can be reproduced from one of the obtained textures. For these textures, some neutrino mass sum rules which relate the neutrino masses and Majorana CP phases will emerge.
In the context of $SU(3)_C \times SU(2)_L \times U(1)_Y \times U(1)_χ$, where $U(1)_χ$ comes from $SO(10) \to SU(5) \times U(1)_χ$, supplemented by the non-Abelian discrete $Δ(27)$ symmetry for three lepton families, Dirac neutrino masses and their mixing are radiatively generated through dark matter. The gauge $U(1)_χ$ symmetry is broken spontaneously. The discrete $Δ(27)$ symmetry is broken softly and spontaneously. Together, they result in two residual symmetries, a global $U(1)_L$ lepton number and a dark symmetry, which may be $Z_2$, $Z_3$, or $U(1)_D$ depending on what scalar breaks $U(1…
We consider charged lepton correction to Tri-bimaximal(TBM) neutrino mixing, defined by the relation $U_{PMNS}=U^{\dagger}_l U_{TB}$ and find possible form of $U_l$ which can impart non-zero value of $\sin θ_{13}$ as well as $\tan^2 θ_{23}<1$, consistent with latest global analysis data. We adopt a new parametrization, other than the standard PDG parametrization, to introduce Dirac CP violating phase $δ$ in the PMNS matrix which is discussed by Fritzsch. Under such charged lepton correction pattern we note that $\tan^2 θ_{12}$ becomes dependent on the CP phase $δ$ from where constraints on $δ$…
We explore the Dirac fermionic and complex scalar dark matter in the framework of a hidden $\mathrm{U}(1)_\mathrm{X}$ gauge theory with kinetic mixing between the $\mathrm{U}(1)_\mathrm{X}$ and $\mathrm{U}(1)_\mathrm{Y}$ gauge fields. The $\mathrm{U}(1)_\mathrm{X}$ gauge symmetry is spontaneously broken due to a hidden Higgs field. The kinetic mixing provides a portal between dark matter and standard model particles. Besides, an additional Higgs portal can be realized in the complex scalar case. Dark matter interactions with nucleons are typically isospin violating, and direct detection constr…
We report a set of exact formulae for computing Dirac masses, mixings, and CP-violation parameter(s) from 3$\times$3 Yukawa matrices $Y$ valid when $Y Y^\dagger \rightarrow U^\dagger \,Y Y^\dagger \, U$ under global $U(3)_{Q_L}$ flavour symmetry transformations $U$. The results apply to the Standard Model Effective Field Theory (SMEFT) and its `geometric' realization (geoSMEFT). We thereby complete, in the Dirac flavour sector, the catalogue of geoSMEFT parameters derived at all orders in the $\sqrt{2 \langle H^\dagger H \rangle} / Λ$ expansion. The formalism is basis-independent, and can be a…
Using the fact that the neutrino mixing matrix $U = U^\dagger_{e}U_ν$, where $U_{e}$ and $U_ν$ result from the diagonalisation of the charged lepton and neutrino mass matrices, we analyse the predictions based on the sum rules which the Dirac phase $δ$ present in $U$ satisfies when $U_ν$ has a form dictated by, or associated with, discrete flavour symmetries and $U_e$ has a "minimal" form (in terms of angles and phases it contains) that can provide the requisite corrections to $U_ν$, so that the reactor, atmospheric and solar neutrino mixing angles $θ_{13}$, $θ_{23}$ and $θ_{12}$ have values c…
The neutrino mixing parameters are thoroughly studied using renormalization-group evolution of Dirac neutrinos with recently proposed parametrization of the neutrino mixing angles referred as `high-scale mixing relations'. The correlations among all neutrino mixing and $CP$ violating observables are investigated. The predictions for the neutrino mixing angle $θ_{23}$ are precise, and could be easily tested by ongoing and future experiments. We observe that the high scale mixing unification hypothesis is incompatible with Dirac neutrinos due to updated experimental data.
We considered a model where |V_{13}|=0 so that delta=0 at M_R and analyzed mixing angles and CP violation angles at the low energy scale by using the renormalization group in the MSSM model. In this model, parameters at M_R scale are two mixing angles (theta_{12} and theta_{23}), three neutrino masses, and two Majorana phases. We found that (1) sin^2 2 theta_{12} at the low energy scale must be less than that at $M_R$ scale, (2) the induced |V_{13}| can be as large as 0.05 if masses of neutrinos are around 0.05 eV.
The recent results from T2K and MINOS experiments point towards a relatively large value of the reactor angle θ_13 in the lepton sector. In this paper we show how a large θ_13 can arise from the charged lepton sector alone in the context of an SU(5) GUT. In such a scenario (tri-)bimaximal mixing in the neutrino sector is still a viable possibility. We also analyse the general implications of the considered scenario for the searches of CP violation in neutrino oscillations.
For the milli-charged Dirac dark matter in the Stueckelberg Z' model, we discuss the contributions from the vector couplings of the dark matter with the neutral gauge bosons to the spin-independent scattering cross section in the direct detections. We also compute the effective coupling between the fermionic dark matter particle and the standard model Higgs boson generated through a triangular loop of Z and/or Z' bosons which may contribute to the spin-independent scattering cross section at the quantum level. We show that the latter contribution is consistent with the most recent experimental…
Various extensions of the Standard Model predict the existence of hidden photons kinetically mixing with the ordinary photon. This mixing leads to oscillations between photons and hidden photons, analogous to the observed oscillations between different neutrino flavors. In this context, we derive new bounds on the photon-hidden photon mixing parameters using the high precision cosmic microwave background spectral data collected by the Far Infrared Absolute Spectrophotometer instrument on board of the Cosmic Background Explorer. Requiring the distortions of the CMB induced by the photon-hidden …
We update and improve past efforts to predict the leptonic Dirac CP-violating phase with models that predict perturbatively modified tribimaximal or bimaximal mixing. Simple perturbations are applied to both mixing patterns in the form of rotations between two sectors. By translating these perturbed mixing matrices to the standard parameterization for the neutrino mixing matrix we derive relations between the Dirac CP-phase and the oscillation angles. We use these relations together with current experimental results to constrain the allowed range for the CP-phase and determine its probability …
The existence of dark sectors, consisting of weakly-coupled particles that do not interact with the known Standard Model forces, is theoretically and phenomenologically motivated. The hidden particles are candidates for Dark Matter and can interact with photon through electric dipole moment (EDM) and magnetic dipole moment (MDM). We investigate the possibility a hidden sector's Dark Matter which is charged under a hidden $U(1)_X$ gauge symmetry can interact with photon at loop level. We evaluate the scattering cross section of hidden Dirac fermion with nuclei and set bounds for dipole moment. …
In the Stueckelberg extension of the Standard Model (StSM), matter in the hidden sector can act as dark matter. Due to an interplay of mixings produced by the usual Higgs mechanism and the Stueckelberg mechanism in the neutral gauge boson sector, the hidden sector matter acquires a milli charge. The Stueckelberg extension also produces a narrow width Z prime which is detectable at the Large Hadron Collider. The hidden sector dark matter naturally explains the PAMELA positron excess by means of a Breit-Wigner enhancement through a Z prime resonance. We also discuss the origin of milli charge in…
We derive the canonical form of mixing of the mass eigenstates in the lepto-quark sector of the 4-generation Dirac-Kaehler extension of the SM (DK-SM) [1,2]. The 4 x 4 CKM matrix of DK-SM is expressed in terms two U(2) matrices. It depends on 2 real parameters and 3 phases. The resulting observed 3 x 3 CKM matrix exhibits previously unknown tree-level algebraic relations among its elements. The simplest two, V_ts = V_cb and V_cs = V_tb, are supported by the experimental data [3]. The 4 x 4 CKM matrix can be fully reconstructed from the experimental values of the 3 x 3 CKM matrix. Thus, except …
In this paper, we derive in a novel approach the possible textures of neutrino mass matrix that can lead to maximal atmospherical mixing angle ($θ^{}_{23} = π/4$) and Dirac CP phase ($δ= - π/2$) in two phenomenologically appealing scenarios: (1) one neutrino mass matrix element being vanishing (2) one neutrino mass being vanishing. For the obtained textures, some neutrino mass sum rules which relate the neutrino masses and mixing parameters will emerge. With the help of these sum rules, the unknown absolute neutrino mass scale and Majorana CP phases can be determined. Some discussions about th…
The standard model left-handed neutrinos and several right-handed neutrinos can obtain a tiny Dirac mass matrix through their mixings with relatively heavy Dirac fermions. In this Dirac seesaw scenario, the mixings involving the left-handed neutrinos can be allowed much larger than those involving the right-handed neutrinos. This undemocratic parameter choice is attractive to phenomenology. We show that the small mixings between the heavy Dirac fermions and the right-handed neutrinos can have a common origin with the observed baryon asymmetry in the universe. We also connect the introduction o…
A descriptive summary is given of the results to-date from the framed standard model (FSM) which: (i) assigns geometric meaning to the Higgs field and to fermion generations, hence offering an explanation for the observed mass and mixing patterns of quarks and leptons, reproducing near-quantitatively 17 of SM parameters with only 7, (ii) predicts a new vector boson $G$ which mixes with $γ$ and $Z$, leading to deviations from the SM mixing scheme. For $m_G > 1$ TeV, these deviations are within present experimental errors but should soon be detectable at LHC when experimental accuracy is further…
In the light of the recent measurement of the leptonic mixing angle $θ_{13}$, implications of the latest mixing data have been investigated for non-minimal textures of lepton mass matrices pertaining to Dirac neutrinos. All 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. The implications of all the three lepton mixing angles have been investigated on the lightest neutrino mass as well as the Jarlskog's CP violating parameter in the leptoni…
In view of the observed strong hierarchy of the quark and lepton masses and of the flavor mixing angles it is argued that the description of flavor mixing must take this into account. One particular interesting way to describe the flavor mixing, which, however, is not the one used today, emerges, which is particularly suited for models of quark mass matrices based on flavor symmetries. We conclude that the unitarity triangle important for B physics should be close to or identical to a rectangular triangle. CP violation is maximal in this sense.
We explore the implications of recent results relating the Dirac CP-violating phase to predicted and measured leptonic mixing angles within a standard set of theoretical scenarios in which charged lepton corrections are responsible for generating a non-zero value of the reactor mixing angle. We employ a full set of leptonic sum rules as required by the unitarity of the lepton mixing matrix, which can be reduced to predictions for the observable mixing angles and the Dirac CP-violating phase in terms of model parameters. These sum rules are investigated within a given set of theoretical scenari…
Numerous papers deal with the phenomenology related to photon-hidden photon kinetic mixing and with the effects of a mass mixing on particle-hidden particle oscillations. In addition, recent papers underline the existence of a geometrical mixing between branes which would allow a matter swapping between branes. These approaches and their phenomenologies are reminiscent of each other but rely on different physical concepts. In the present paper, we suggest there is no rivalry between these models, which are probably many faces of the same physics. We discuss some phenomenological consequences o…
The premise of an organizing quadratic hierarchy rule in lepton-quark flavor physics was used earlier for explanation of the hierarchy patterns of four generic pairs of flavor quantities 1) charged-lepton and 2) neutrino deviations from mass-degeneracy, 3) deviations of lepton mixing from maximal magnitude and 4) deviations of quark mixing from minimal one. Here it is shown that the quadratic hierarchy equation that is uniquely related to three flavor particle generations may have yet another important function. It determines two complementary values of the Dirac CP-violating phases in the qua…
We present a SUSY breaking scenario based on Abelian gaugino kinetic term mixings between hidden and observable sectors. If an extra U(1) gaugino in the observable sector obtains a large mass through this mixing effect based on SUSY breaking in the hidden sector, soft SUSY breaking parameters in the MSSM may be affected by radiative effects due to this gaugino mass. New phenomenological aspects are discussed in such a SUSY breaking scenario.
Relation between the lepton and quark mixings: $U_{PMNS} \approx V_{CKM}^{\dagger} U_X$, where $U_X$ is the BM or TBM mixing matrices, implies the quark-lepton (Grand) unification and existence of hidden sector with certain flavor symmetries. The latter couples to the visible sector via the neutrino portal and is responsible for $U_X$, as well as for smallness of neutrino mass. GUT ensures appearance of $\sim V_{CKM}$ in the lepton mixing. General features of this scenario (inverse or double seesaw, screening of the Dirac structures, basis fixing symmetry) are described and two realizations ar…
We demonstrate that only two ansatz can produce the features of the neutrino mixing angles. The first ansatz comes from the quark-lepton grand unification; $ν_{Di} = V_{CKM} ν_α$ is satisfied for left-handed neutrinos, where $ν_{Di}$ are the Dirac mass eigenstates and $ν_α$ are the flavour eigenstates. The second ansatz comes from the assumption; $ν_{Di} = U_{bimaximal} ν_{i}$ is satisfied between the Dirac mass eigenstates $ν_{Di}$ and the light Majorana neutrino mass eigenstates $ν_{i}$, where $U_{bimaximal}$ is the bimaximal mixing matrix. By these two ansatz, the Maki-Nakagawa-Sakata matri…
A TeV-scale Higgs doublet with a small mixing to the standard model Higgs doublet can have the sizable Yukawa couplings to several right-handed neutrinos and the standard model lepton doublets. This provides a testable Dirac neutrino mass generation. We further consider a seesaw mechanism involving a $U(1)_{B-L}^{}$ gauge symmetry, which predicts the existence of two right-handed neutrinos and a stable Dirac fermionic dark matter, to simultaneously explain the small mixing between the two Higgs doublets and the generation of the cosmic baryon asymmetry.
A simple mechanism to generate Dirac masses for the neutrinos in SU(5) supersymmetric grand unified theory is proposed. The tiny Dirac masses are induced by the small mixing between the Higgs fields and another superheavy fields. The mixing terms are obtained by the same mechanism as the mu-term generation of the order of the supersymmetry breaking scale, so that the mixing of order TeV / M_GUT \sim 10^{-13} is realized. We consider the lepton flavor violating processes in this model. The branching ratios are directly related to the neutrino oscillation parameters and we can predict the B(τ-> …
A TeV-scale Higgs doublet can acquire a tiny vacuum expectation value via its small mixing with the standard model Higgs doublet. Ones then can realize a testable Dirac neutrino mass generation through the sizable Yukawa couplings among this new Higgs doublet, several right-handed neutrinos and the standard model lepton doublets. We show the small mixing between the two Higgs doublets can come from certain interactions for generating the cosmic baryon asymmetry.
We consider the mechanism of screening of the Dirac flavor structure in the context of the double seesaw mechanism. As a consequence of screening, the structure of the light neutrino mass matrix, m_ν, is determined essentially by the structure of the (Majorana) mass matrix, M_S, of new super-heavy (Planck scale) neutral fermions S. We calculate effects of the renormalization group running in order to investigate the stability of the screening mechanism with respect to radiative corrections. We find that screening is stable in the supersymmetric case, whereas in the standard model it is unstabl…
Three of the viable solutions of the solar neutrino problem are consistent with close to maximal leptonic mixing: $\sin^2θ_{12}={1\over2}(1-ε_{12})$ with $|ε_{12}|\ll1$. Flavor models can naturally explain close to maximal mixing if approximate horizontal symmetries force a pseudo-Dirac structure on the neutrino mass matrix. An experimental determination of $|ε_{12}|$ and sign($ε_{12}$) can constrain the structure of the lepton mass matrices and consequently provide stringent tests of such flavor models. If both $|ε_{12}|$ and $Δm^2_{21}$ are known, it may be possible to estimate the mass scal…
An explicit model of neutrino texture is presented, where in the 6 times 6 mass matrix the Majorana lefthanded component is zero, the Majorana righthanded component - diagonal with equal entries, and the Dirac component gets a hierarchical structure, deformed by nearly bimaximal mixing. If the Majorana righthanded component dominates over the Dirac component, the familiar seesaw mechanism leads effectively to the popular, nearly bimaximal oscillations of active neutrinos. The Dirac component, before its deformation, may be similar in shape to the charged-lepton and quark mass matrices. Then, p…
CP violation in neutrino interactions is described by three phases contained in Pontecorvo-Maki-Nakagawa-Sakata mixing matrix ($U_{PMNS}$). We argue that the phenomenologocally consistent result of the Dirac CP violation can be obtained if $U_{PMNS}$ is constructed along bipair neutrino mixing scheme, namely, requiring that $ | U_{12} | = | U_{32} | {\rm and} | U_{22} | = | U_{23} | (\rm case 1)$ and $ | U_{12} | = | U_{22} | {\rm and} | U_{32} | = | U_{33}| (\rm case 2)$, where $U_{ij}$ stands for the $i$-$j$ matrix element of $U_{PMNS}$. As a results, the solar, atmospheric and reactor neutr…
We discuss the Dirac CP violating phase $δ_{CP}$ in the Froggatt-Nielsen model for a neutrino mass matrix $M_ν$ imposing a condition ${\rm det} [M_ν]=0$. This additional condition restricts the CP violating phase $δ_{CP}$ drastically. We find that the phase $δ_{CP}$ is predicted in the region of $\pm (0.4- 2.9)$ radian, which is consistent with the recent T2K and NO$ν$A data. There is a remarkable correlation between $δ_{CP}$ and $\sin^2θ_{23}$. The phase $δ_{CP}$ converges on $\sim \pm π/2$ if $\sin^2θ_{23}$ is larger than $0.5$. Thus, accurate measurements of $\sin^2θ_{23}$ are important for…
A kinetic mixing term, which generalizes the duality symmetry of Dirac, is studied in a theory with two photons (visible and hidden). This theory can be either CP conserving or CP violating depending on the transformation of fields in the hidden sector. However if CP is violated, it necessarily occurs in the hidden sector. This opens up an interesting possibility of new sources of CP violation.
We consider the neutrino masses and mixing in the framework of SO(10) GUTs with hidden sector consisting of fermionic and bosonic SO(10) singlets and flavor symmetries. The framework allows to disentangle the CKM physics responsible for the CKM mixing and different mass hierarchies of quarks and leptons and the neutrino new physics which produces smallness of neutrino masses and large lepton mixing. The framework leads naturally to the relation $U_{PMNS} \sim V_{CKM}^{\dagger} U_0$, where structure of $U_0$ is determined by the flavor symmetry. The key feature of the framework is that apart fr…
We derive predictions for the Dirac phase $δ$ present in the $3\times 3$ unitary neutrino mixing matrix $U = U_e^{\dagger} \, U_ν$, where $U_e$ and $U_ν$ are $3\times 3$ unitary matrices which arise from the diagonalisation, respectively, of the charged lepton and the neutrino mass matrices. We consider forms of $U_e$ and $U_ν$ allowing us to express $δ$ as a function of three neutrino mixing angles, present in $U$, and the angles contained in $U_ν$. We consider several forms of $U_ν$ determined by, or associated with, symmetries, tri-bimaximal, bimaximal, etc., for which the angles in $U_ν$ a…
We analyze the power of the Tevatron dataset to exclude or discover fourth generation neutrinos. In a general framework, one can have mixed left- and right-handed neutrinos, with Dirac and Majorana neutrinos as extreme cases. We demonstrate that a single Tevatron experiment can make powerful statements across the entire mixing space, extending LEP's mass limits of 60-80 GeV up to 150-175 GeV, depending on the mixing.
We discuss neutrino masses and mixing in the context of seesaw type I models with three right-handed Majorana neutrinos and an approximately diagonal Dirac sector. This ansatz is motivated by the idea that the flavor structure in the right-handed Majorana masses is responsible for the large mixing angles, whereas the small mixing angle $θ_{13}$ originates from the Dirac Yukawa couplings in analogy to the quark sector. To obtain $θ_{13} \approx 0.15$ we study a possible $SU(5)$ grand unified theory realization with a $U(1) \times \mathbb{Z}'_2 \times \mathbb{Z}''_2 \times \mathbb{Z}'''_2$ flavo…
The seesaw enhancement of the bi-large mixings are discussed for the two-zero textures of the neutrino mass matrix. There are no large mixings in both Dirac neutrino mass matrix $m_D$ and right-handed Majorana neutrino mass matrix $M_R$, however, the bi-large mixing is realized via the seesaw mechanism. We present twelve sets of $m_D$ and $M_R$ for the seesaw enhancement and discuss the related phenomena, the $μ\to e+γ$ process and the leptogenesis. The decay rate of $μ\to e+γ$ is enough suppressed due to zeros in the Dirac neutrino mass matrix. Six $m_D$ lead to the lepton asymmetry, which ca…
