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Register a new userFour Zero Neutrino Yukawa Textures in the Minimal Seesaw Framework
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We investigate, within the Type I seesaw framework, the physical implications of zero textures in the Yukawa couplings which generate the neutrino Dirac mass matrix $m_D$. It is shown that four is the maximal number of texture zeroes compatible with the observed leptonic mixing and the assumption that no neutrino mass vanishes. We classify all allowed four-zero textures of $m_D$ into two categories with three classes each. We show that the different classes, in general, admit CP violation both at low and high energies. We further present the constraints obtained for low energy physics in each case. The r^ ole of these zero textures in establishing a connection between leptogenesis and low energy data is analysed in detail. It is shown that it is possible in all cases to completely specify the parameters relevant for leptogenesis in terms of light neutrino masses and leptonic mixing together with the unknown heavy neutrino masses.
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For type I seesaw and in the basis where the charged lepton and heavy right-handed neutrino mass matrices are real and diagonal, four has been shown to be the maximum number of zeros allowed in the neutrino Yukawa coupling matrix $Y_ u$. These four zero textures have been classified into two distinct categories. We investigate certain phenomenological consequences of these textures within a supersymmetric framework. This is done by using conditions implied on elements of the neutrino Majorana mass matrix for textures of each category in $Y_ u$. These conditions turn out to be stable under radiative corrections. Including the effective mass, which appears in neutrinoless double beta decay, along with the usual neutrino masses, mixing angles and phases, it is shown analytically and through scatter plots how restricted regions in the seesaw parameter space are selected by these conditions. We also make consequential statements on the yet unobserved radiative lepton flavor violating decays such as $mu to e gamma$. All these decay amplitudes are proportional to the moduli of entries of the neutrino Majorana mass matrix. We also show under which conditions the low energy CP violation, showing up in neutrino oscillations, is directly linked to the CP violation required for producing successful flavor dependent and flavor independent lepton asymmetries during leptogenesis.
The presence of a zero texture in the neutrino mass matrix can indicate the presence of an underlying symmetry which can generate neutrino mass and mixing. In this paper, for the first time we study the four-zero textures of the low energy neutrino mass matrix in the presence of an extra light-sterile neutrino i.e., the 3+1 neutrino scheme. In our analysis we find that out of the 210 possible four-zero textures only 15 textures are allowed. We divide the allowed four-zero textures into two classes -- class $A$ in which the value of mass matrix element $M_{ee}$ is zero and class $B$ in which $M_{ee}$ is non-zero. In this way we obtain ten possible four-zero textures in class $A$ and five possible four-zero textures in class $B$. In our analysis we find that, for normal hierarchy the allowed number of textures in class $A$ ($B$) is nine (three). For the case of inverted hierarchy we find that, two textures in class $A$ are disallowed and these textures are different from the disallowed textures for normal hierarchy in class $A$. However, we find that all the five textures in class $B$ are allowed for the inverted hierarchy. Based on analytic expressions for the elements $M_{alphabeta}$, we discuss the reasons for certain textures being disallowed. We also discuss the correlations between the different parameters of the allowed textures. Finally, we present the implications of our study on experimental searches for neutrinoless double beta decay.
We study a model of neutrino and dark matter within the framework of a minimal extended seesaw. This model is based on $A_4$ flavour symmetry along with the discrete $Z_3times Z_4$ symmetry to stabilize the dark matter and construct desired mass matrices for neutrino mass. Five-zero textures are imposed in the final $4times4$ active-sterile mass matrix, which significantly reduces free parameter in the model. Three right-handed neutrinos were considered, two of them have nearly degenerate masses which help us to achieve baryogenesis via resonant leptogenesis. A singlet fermion (sterile neutrino) with mass $simmathcal{O}$(eV) is also considered, and we are able to put bounds on active-sterile mixing parameters via neutrino oscillation data. Resonant enhancement of lepton asymmetry is studied at TeV scale, where we discuss a few aspects of baryogenesis considering the flavour effects. Possibility of improvement in effective mass from $0 ubetabeta$ in the presence of a single generation of sterile neutrino flavour is also studied within the fermion sector. In the scalar sector, the imaginary component of the complex singlet scalar is behaving as a potential dark matter candidate and simultaneously the real part of the complex scalar is associated with the fermion sector for sterile mass generation. A broad region of dark matter mass is analyzed from various annihilation processes, and the VEV of the complex scalar plays a pivotal role to achieve the observed relic density at the right ballpark.
We investigate Linear and Inverse seesaw mechanisms with maximal zero textures of the constituent matrices subjected to the assumption of non-zero eigenvalues for the neutrino mass matrix $m_ u$ and charged lepton mass matrix $m_e$. If we restrict to the minimally parametrized non-singular `$m_e$ (i.e., with maximum number of zeros) it gives rise to only 6 possible textures of $m_e$. Non-zero determinant of $m_ u$ dictates six possible textures of the constituent matrices. We ask in this minimalistic approach, what are the phenomenologically allowed maximum zero textures are possible. It turns out that Inverse seesaw leads to 7 allowed two-zero textures while the Linear seesaw leads to only one. In Inverse seesaw, we show that 2 is the maximum number of independent zeros that can be inserted into $mu_S$ to obtain all 7 viable two-zero textures of $m_ u$. On the other hand, in Linear seesaw mechanism, the minimal scheme allows maximum 5 zeros to be accommodated in `$m$ so as to obtain viable effective neutrino mass matrices ($m_ u$). Interestingly, we find that our minimalistic approach in Inverse seesaw leads to a realization of all the phenomenologically allowed two-zero textures whereas in Linear seesaw only one such texture is viable. Next our numerical analysis shows that none of the two-zero textures give rise to enough CP violation or significant $delta_{CP}$. Therefore, if $delta_{CP}=pi/2$ is established, our minimalistic scheme may still be viable provided we allow more number of parameters in `$m_e$.
The arbitrariness of Yukawa couplings can be reduced by the imposition of some flavor symmetries and/or by the realization of texture zeros. We review neutrino Yukawa textures with zeros within the framework of the type-I seesaw with three heavy right chiral neutrinos and in the basis where the latter and the charged leptons are mass diagonal. An assumed non-vanishing mass of every ultralight neutrino and the observed non-decoupling of any neutrino generation allow a maximum of four zeros in the Yukawa coupling matrix $Y_ u$ in family space. There are seventy two such textures. We show that the requirement of an exact $mutau$ symmetry, coupled with the observational constraints, reduces these seventy two allowed textures to only four corresponding to just two different forms of the light neutrino mass matrix $M_{ u A}/M_{ u B}$, resulting in an inverted/normal mass ordering. The effect of each of these on measurable quantities can be described, apart from an overall factor of the neutrino mass scale, in terms of two real parameters and a phase angle all of which are within very constrained ranges. The masses and Majorana phases of ultralight neutrinos are predicted within definite ranges with $3sigma$ laboratory and cosmological observational inputs. The rate for $0 ubetabeta$ decay, though generally below the reach of planned experiments, could approach it in some parameteric regions. Within the same framework, we also study Yukawa textures with a fewer number of zeros, but with exact $mutau$ symmetry. We further formulate the detailed scheme of the explicit breaking of $mutau$ symmetry in terms of three small parameters for allowed four zero textures. The observed sizable mixing between the first and third generations of neutrinos is shown to follow for a suitable choice of these symmetry breaking parameters.
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