Narrow Results

The consequences of a texture zero at the ee entry of neutrino mass matrix in the flavor basis, which also implies a vanishing effective Majorana mass for neutrinoless double beta decay, have been studied for Majorana neutrinos. The neutrino parameter space under this condition has been constrained in the light of all available neutrino data including the CHOOZ bound on .

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.

We study the existence of one/two texture zeros or one/two vanishing minors in the neutrino mass matrix with μτ symmetry. In the basis where the charged lepton mass matrix and the Dirac neutrino mass matrix are diagonal, the one/two zeros or one/two vanishing minors on the right-handed Majorana mass matrix having μτ symmetry will propagate via seesaw mechanism as one/two vanishing minors or one/two texture zeros in the neutrino mass matrix with μτ symmetry respectively. It is found that only five such texture structures of the neutrino mass matrix are phenomenologically viable. For tribimaximal mixing, these texture structures reduce the number of free parameters to one. Interesting predictions are obtained for the effective Majorana mass M_ee, the absolute mass scale and the Majorana-type CP violating phases.

We have investigated the phenomenological implications of texture one-zero neutrino mass matrix under the lamp post of the latest data on neutrino mass and mixings. In particular, we have obtained the predictions of the model for, yet unknown observables like neutrino mass hierarchy, ${𝜃}_{23}$-octant and CP violation. Out of the six texture one-zero neutrino mass models, $T_1$, $T_2$ and $T_3$ are found to be necessarily CP violating. ${𝜃}_{23}$ can be above or below maximality except for the texture $T_4$ (with NH), wherein ${𝜃}_{23}<45^{\circ }$ at $2.5\sigma$. Also, we have proposed a flavor model based on the non-Abelian group $A_4$ within the paradigm of type-I+II seesaw framework, wherein such textures can be realized.

In the framework of anomaly free $U{(1)}_{L_{\mu }-L_{\tau }}$ model, singlet scalar field with nonzero $L_{\mu }-L_{\tau }$ charge gives rise to massive gauge boson $(Z_{\mu \tau })$ through spontaneous symmetry breaking. $Z_{\mu \tau }$ leads to one loop contribution to the muon anomalous magnetic moment. These scalar fields may, also, appear in the structure of right-handed neutrino mass matrix, thus, connecting the possible explanation of muon $(g-2)$ and low-energy neutrino phenomenology through vevs associated with the scalar fields. In this work, we consider textures of inverse neutrino mass matrix $(M_{\nu }^{-1})$ wherein any two elements of the mass matrix are zero. In this ansatz, with Dirac neutrino mass matrix diagonal, the zero(s) of right-handed Majorana neutrino mass matrix correspond to zero(s) in the low-energy effective neutrino mass matrix (within Type-I seesaw). We have realized two such textures of $M_{\nu }^{-1}$ accommodating the muon $(g-2)$ and low-energy neutrino phenomenology. The requirement of successful explanation of muon $(g-2)$, further, constrains the allowed parameter space of the model and results in sharp correlations amongst neutrino mixing angles and CP invariants. The model explains muon $(g-2)$ for $M_{Z_{\mu \tau }}$ in the range (0.035–0.100 GeV) and $g_{\mu \tau }\approx {𝒪}(10^{-4})$ which is found to be consistent with constraints coming from the current experiments CCFR, COHERENT, BABAR while being within sensitivities of future experiments such as NA62 and NA64.

The Daya Bay and RENO reactor neutrino experiments have revealed that the smallest neutrino mixing angle is in fact relatively large, i.e. θ₁₃ ≈9°. Motivated by this exciting progress, we perform a systematic study of the neutrino mass matrix M_ν with one or two texture zeros, in the assumption that neutrinos are Dirac particles. Among 15 possible patterns with two texture zeros, only three turn out to be favored by current neutrino oscillation data at the 3σ level. Although all the six patterns with one texture zero are compatible with the experimental data at the 3σ level, the parameter space of each pattern is strictly constrained. Phenomenological implications of M_ν on the leptonic CP violation and neutrino mass spectrum are explored, and the stability of texture zeros against the radiative corrections is also discussed.

In this paper, we study all possible neutrino mass matrices with one zero element and two equal nonzero elements, known as hybrid texture neutrino mass matrices. In the diagonal charged lepton basis, we consider 39 such possible cases which are consistent with the latest neutrino data. Using the two constraints on neutrino mass matrix elements imposed by hybrid textures, we numerically evaluate the neutrino parameters like the lightest neutrino mass $m_{\mathrm{\text{lightest}}}$, one Dirac CP phase $\delta$ and two Majorana CP phases $\alpha$, $\beta$ by using the global fit $3\sigma$ values of three mixing angles and two mass squared differences. We then constrain this parameter space by using the cosmological upper bound on the sum of absolute neutrino masses given by Planck experiment. We also calculate the effective neutrino mass $m_{\nu }^{\mathrm{\text{eff}}}$ for this region of parameter space which can have relevance in future neutrinoless double beta decay experiments. We finally discriminate between these hybrid texture mass matrices from the requirement of producing correct baryon asymmetry through type I seesaw leptogenesis. We also constrain the light neutrino parameter space as well as the lightest right-handed neutrino mass from the constraint on baryon asymmetry of the Universe from Planck experiment.

In our work, we study the texture zeros of $m_{\nu }$ in the minimal extended type-I seesaw (MES) with incorporating one extra gauge singlet field “$S$”. The MES models deal with the Dirac neutrino mass matrix $(M_D)$, the right-handed Majorana mass matrix $(M_R)$ and the sterile neutrino mass matrix $(M_S)$. We carry out the mapping of all possible zero textures of $M_D$, $M_R$ and $M_S$ for phenomenologically predictive cases having total eight zeros of $M_D$ and $M_R$ studied in the literature. With this motivation, we consider (a) $(4+4)$ scheme, (b) $(5+3)$ scheme and (c) $(6+2)$ scheme, where the digits of a pair represent the number of zeros of $M_D$ and $M_R$, respectively along with the one zero and two zero textures of $(M_S)$. There are a large number of possibilities of zeros of fermion mass matrices but the implementation of $S_3$ transformations reduces it to a very minimum number of basic structures. Interestingly out of four allowed one zero textures of $m_{\nu }$ without sterile neutrino, only three cases ($m_{e\tau }=0$, $m_{\mu \mu }=0$ and $m_{\tau \tau }=0$) are allowed in MES mechanism for the $(4+4)$ and $(5+3)$ schemes. We find some correlations for different combination of $M_D$, $M_R$ and $M_S$ on enforcement of zeros. We examined all the correlations under the recent neutrino oscillation data and find that only $m_{\tau \tau }=0$ survives while both $m_{e\tau }=0$ and $m_{\mu \mu }=0$ are ruled out. Interestingly the one zero textures inherently represent the inverted hierarchy of the mass ordering of light neutrinos. No two zero textures of $m_{\nu }$ survive in MES although there are a number of allowed structures phenomenologically. The allowed texture zeros are finally realized using a discrete Abelian flavor symmetry group $Z_7$ with the extension of standard model to include some scalar fields.

We study the texture zeros of $4\times 4$ neutrino mass matrices $M_{\nu }$ in the minimal extended type-I seesaw (MES) mechanism, incorporating one extra gauge singlet field “$S$”. The $4\times 4$  MES model deals with $3\times 3$  $(M_D)$, $3\times 3$  $(M_R)$ and $1\times 3$ mass matrix $(M_S)$ which couples the right-handed neutrinos and the singlet field “$S$”. We carry out the mapping of all possible zero textures of $M_D$, $M_R$ and $M_S$ with the restriction to phenomenologically predictive cases having total eight zeros of $M_D$ and $M_R$ studied in the literature. If $m_s$, the sterile neutrino mass, is subject to any limit, further block diagonalization of $M_{\nu }$ shall not be allowed to reduce it to a $3\times 3$ matrix. In $4\times 4$  $M_{\nu }$ scenario, the study of texture zero is totally different and interesting. With this motivation, we consider the $(4+4)$ scheme where the digits of the pair represent the number of zeros of $M_D$ and $M_R$, respectively, along with the one/two-zero textures of $M_S$. There are a large number of possibilities of zeros of fermion mass matrices, but the implementation of $S_3$ transformations reduces it to a very minimum number of basic structures. As the $4\times 4$ MES matrix is a matrix of rank 3, so we consider only those textures with two zeros which are of rank 3 whereby the number of feasible zero textures reduces to 12, out of 15. On realizing these 12 textures under MES mechanism with $(4+4)$ picture, we arrive at certain correlations for each texture. We examine the viability of each texture by scanning their respective correlations under recent neutrino oscillation data. Also, we discuss the interplay of Dirac and Majorana CP phases in determining the viability of a texture. The allowed two-zero textures are finally realized using a discrete Abelian flavor symmetry group $Z_9$ with the extension of Standard Model to include some scalar fields.

The strong mass hierarchy, flavor mixing pattern and CP violation in the quark sector have been long-standing puzzles in the Standard Model. Thanks to the elegant neutrino oscillation experiments in the past few decades, now we know that neutrinos are massive and lepton flavor mixing is significant. The flavor puzzles have extended to the lepton sector. In this article, we explain how the idea of texture zeros applies to understand lepton flavor mixing, and emphasize that it is particularly useful for exploring the underlying dynamics or symmetries for lepton flavor mixing.

A randomly generated complex symmetric matrix using the adaptive Monte Carlo method is taken as a general form of Majorana neutrino mass matrix, which is diagonalized by the use of eigenvectors. We extract all the neutrino oscillation parameters, i.e. two mass-squared differences ($\mathrm{\Delta }{m}_{21}^2$ and $\mathrm{\Delta }{m}_{32}^2$), three mixing angles (${\theta }_{12}$, ${\theta }_{13}$, ${\theta }_{23}$) and three phases, i.e. one Dirac CP violating phase (${\delta }_{\mathrm{\text{CP}}}$) and two Majorana phases (${\alpha }_1$ and ${\alpha }_2$). The Charge-Parity (CP) violating phases are extracted from the mixing matrix constructed with the eigenvectors of the Hermitian matrix formed by the complex symmetric mass matrix. All the latest neutrino oscillation parameters within 3$\sigma$ bound are only allowed in Normal Hierarchy (NH) consistent with the latest Planck cosmological upper bound, $\sum |m_i|<0.12$eV. Three cases of one-zero texture i.e. $m_{11}=0$, $m_{12}=0$, $m_{13}=0$ and two cases of two-zero texture, i.e. $m_{11},m_{12}=0$ and $m_{11},m_{13}=0$ are allowed in normal hierarchy whereas none of zero texture is allowed in inverted hierarchy. We also study effective neutrino masses $m_{\beta }$ in tritium beta decay and $m_{\beta \beta }$ in neutrinoless double beta decay and calculate numerically the allowed range of mass elements of Majorana mass matrix.

The strong mass hierarchy, flavor mixing pattern and CP violation in the quark sector have been long-standing puzzles in the Standard Model. Thanks to the elegant neutrino oscillation experiments in the past few decades, now we know that neutrinos are massive and lepton flavor mixing is significant. The flavor puzzles have extended to the lepton sector. In this article, we explain how the idea of texture zeros applies to understand lepton flavor mixing, and emphasize that it is particularly useful for exploring the underlying dynamics or symmetries for lepton flavor mixing.

Four is the maximum number of texture zeros allowed in the Yukawa coupling matrix of three massive neutrinos. These completely fix the high scale CP violation needed for leptogenesis in terms of that accessible at laboratory energies. μτ symmetry drastically reduces such allowed textures. Only one form of the light neutrinos mass matrix survives comfortably while another is marginally allowed.