arXiv subjects

Roopam Sinha

Publications and source records attributed to Roopam Sinha.

5 recordsLinked to original sources

arXiv2018

Phenomenological implications of the Friedberg-Lee transformation in a neutrino mass model with $\mu\tau$-flavored CP symmetry

We propose a neutrino mass model with $\mu\tau$-flavored CP symmetry, where the effective light neutrino Lagrangian enjoys an additional invariance under a Friedberg-Lee (FL) transformation on the left-handed flavor neutrino fields, that leads to a highly predictive and testable scenario. While both types of the light neutrino mass ordering, i.e., Normal Ordering (NO) as well as the Inverted Ordering (IO) are allowed, the absolute scale of neutrino masses is fixed by the vanishing determinant of light Majorana neutrino mass matrix $M_\nu$. We show that for both types of mass ordering, whilst the atmospheric mixing angle $\theta_{23}$ is in general nonmaximal ($\theta_{23}\neq \pi/4$), the Dirac CP phase $\delta$ is exactly maximal ($\delta=\pi/2,3\pi/2$) for IO and nearly maximal for NO owing to $\cos\delta\propto \sin\theta_{13}$. For the NO, very tiny nonvanishing Majorana CP violation might appear through one of the Majorana phases $\beta$; otherwise the model predicts vanishing Majorana CP violation. Thus, despite the fact, that from the measurement of $\theta_{23}$, it is difficult to rule out the model, any large deviation of $\delta$ from its maximality, will surely falsify the scenario. For a comprehensive numerical analysis, beside fitting the neutrino oscillation global fit data, we also present a study on the $\nu_\mu\rightarrow \nu_e$ oscillation which is expected to show up Dirac CP violation in different long baseline experiments. Finally, assuming purely astrophysical sources, we calculate the Ultra High Energy (UHE) neutrino flavor flux ratios at neutrino telescopes, such as IceCube, from which statements on the octant of $\theta_{23}$ could be made in our model.

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arXiv2018

CP transformed mixed $\mu\tau$ antisymmetry for neutrinos and its consequences

We propose a complex extension of mixed $\mu\tau$ antisymmetry in the neutrino Majorana mass matrix $M_\nu$. This can be implemented in the Lagrangian by a generalized CP transformation (labeled by a mixing parameter $\theta$) on the left-chiral flavor neutrino fields. We investigate its implications for leptonic CP violation and neutrino phenomenology in general. Interestingly, the $\mu\tau$ mixing parameter $\theta$ gets correlated with the Dirac CP phase $\delta$ and the atmospheric mixing angle $\theta_{23}$ through an analytical relation. In general, for arbitrary $\theta$, both $\theta_{23}$ and $\delta$ are nonmaximal. We discuss the corresponding results for the CP asymmetry parameter $A_{\mu e}$ in neutrino oscillation experiments. For a nonmaximal $\delta$, one of the two Majorana phases is different from $0$ or $\pi$, thereby leading to nonvanishing Majorana CP violation with observable consequences for the neutrinoless double beta ($\beta\beta0\nu$) decay process. We numerically work out in detail the predictions for that process in relation to various ongoing and forthcoming experiments. We also work out the predictions of our scheme on flavor flux ratios at neutrino telescopes. While exact CP transformed $\mu\tau$ interchange antisymmetry ($\theta=\pi/2$) leads to an exact equality among those ratios, taking a value $0.5$, a tiny deviation can cause a drastic change in them. Careful measurement of these flux ratios in future will further constrain the parameter $\theta$.

hep-ph↗

arXiv2018

Importance of generalized $\mu\tau$ symmetry and its CP extension on neutrino mixing and leptogenesis

Within the framework of residual symmetry, two $\mathbb{Z}_2$ type associate $\mu\tau$ interchange symmetries robustly constrain the Dirac CP phase $\delta$ in a model independent way. Both of them predict simultaneous maximality of $\delta$ and the atmospheric mixing angle $\theta_{23}$. We show how these well known correlations will be changed if we generalize the $\mu\tau$ interchange symmetry to a $\mu\tau$ mixing symmetry. In particular, we show that the stringent condition of simultaneous maximality could be relaxed even with a very small departure from the exact $\mu\tau$ interchange. In addition, the present neutrino data on $\delta$ and $\theta_{23}$ can be explained better by the mixing symmetry. After discussing the impact of the $\mu\tau$ mixing in some realistic neutrino mass models, we show how the proposed mixing could be realized with two simultaneous CP transformations which also lead to novel and testable correlations between $\delta$ and the mixing angles $\theta_{ij}$. Next we discuss in particular, the `three flavour regime' of leptogenesis within the CP extended framework and show, unlike the ordinary CP extended $\mu\tau$ interchange symmetry, a resonant leptogenesis is possible due the generalization of $\mu\tau$ interchange to the $\mu\tau$ mixing and the resulting baryon asymmetry always requires a nonmaximal $\theta_{23}$ owing to the fact that the baryon to photon ratio $\eta_B$ vanishes in the exact limit of $\theta_{23}=\pi/4$. This is one of the robust predictions of this framework. The CP extended $\mu\tau$ mixing is also a novel example of a low energy effective model that provides an important insight to the off-diagonal terms of the flavour coupling matrix which have usually been neglected in literature to compute the final baryon asymmetry, in particular in the models with flavour symmetries.

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arXiv2017

Generalized $\mathbb{Z}_2\times \mathbb{Z}_2$ in Scaling neutrino Majorana mass matrix and baryogenesis via flavored leptogenesis

We investigate the consequences of a generalized $\mathbb{Z}_2\times\mathbb{Z}_2$ symmetry on a scaling neutrino Majorana mass matrix. It enables us to determine definite analytical relations between the mixing angles $\theta_{12}$ and $\theta_{13}$, maximal CP violation for the Dirac type and vanishing for the Majorana type. Beside the other testable predictions on the low energy neutrino parameters such as $\beta\beta_{0\nu}$ decay matrix element $|M_{ee}|$ and the light neutrino masses $m_{1,2,3}$, the model also has intriguing consequences from the perspective of leptogenesis. With the assumption that the required CP violation for leptogenesis is created by the decay of lightest ($N_1$) of the heavy Majorana neutrinos, only $\tau$-flavored leptogenesis scenario is found to be allowed in this model. For a normal (inverted) ordering of light neutrino masses, $\theta_{23}$ is found be less (greater) than its maximal value, for the final baryon asymmetry $Y_B$ to be in the observed range. Besides, an upper and a lower bound on the mass of $N_1$ have also been estimated. Effect of the heavier neutrinos $N_{2,3}$ on final $Y_B$ has been worked out subsequently. The predictions of this model will be tested in the experiments such as nEXO, LEGEND, GERDA-II, T2K, NO$\nu$A, DUNE etc.

hep-ph↗

arXiv2015

Maximal Zero Textures in Linear and Inverse Seesaw

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 $m_\nu$ 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 $m_\nu$ 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 $m_\nu$. 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 ($m_\nu$). 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 `$m_e$'.

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