arXiv subjects

Surender Verma

Publications and source records attributed to Surender Verma.

At least 37 records · Page 2Linked to original sources

arXiv2022

Gauged $U(1)_{L_μ-L_τ}$ Symmetry and two-zero Textures of Inverse Neutrino Mass Matrix in light of Muon ($g-2$)

In the framework of anomaly free $U(1)_{L_μ-L_τ}$ model, charged scalar fields give rise to massive gauge boson ($Z_{μτ}$) through spontaneous symmetry breaking. $Z_{μτ}$ 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 the present work, we consider textures of inverse neutrino mass matrix ($M_ν^{-1}$) 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 $M_ν^{-1}$ accommodating the muon ($g-2$) and low energy neutrino phenomenology. The requirement of successful explanation of muon ($g-2$), further, constrain the allowed parameter space of the model and results in sharp correlations amongst neutrino mixing angles, $CP$ invariants and effective Majorana mass ($M_{ee}$). The model explains muon ($g-2$) for $M_{Z_{μτ}}$ in the range ($0.035$ GeV-$0.100$ GeV) and $g_{μτ}\approx\mathcal{O}(10^{-4}$) which is found to be consistent with constraints coming from the experiments like CCFR, COHERENT, BABAR, NA62 and NA64.

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arXiv2022

Muon ($g-2$) in $U(1)_{L_μ-L_τ}$ Scotogenic Model Extended with Vector like Fermion

The latest results of anomalous muon magnetic moment at Fermilab show a discrepancy of 4.2 $σ$ between the Standard Model (SM) prediction and experimental value. In this work, we revisit $U(1)_{L_μ-L_τ}$ symmetry with in the paradigm of scotogenic model which explains muon ($g-2$) and neutrino mass generation, simultaneously. The mass of new gauge boson $M_{Z_{μτ}}$ generated after the spontaneous symmetry breaking of $U(1)_{L_μ-L_τ}$ is constrained, solely, in light of the current neutrino oscillation data to explain muon ($g-2$). In particular, we have obtained two regions I and II, around 150 MeV and 500 MeV, respectively, in $M_{Z_{μτ}}-g_{μτ}$ plane which explain the neutrino phenomenology. Region I is found to be consistent with muon neutrino trident (MNT) bound ($g_{μτ}$ $\leq$ $10^{-3}$) to explain muon ($g-2$), however, region II violates it for mass range $M_{Z_{μτ}}>300$ MeV. We, then, extend the minimal gauged scotogenic model by a vector like lepton (VLL) triplet $ψ_T$. The mixing of $ψ_T$ with inert scalar doublet $η$ leads to chirally enhanced positive contribution to muon anomalous magnetic moment independent of $Z_{μτ}$ mass. Furthermore, we have, also, investigated the implication of the model for $0νββ$ decay and $CP$ violation. The non-observation of $0νββ$ decay down to the sensitivity of 0.01 eV shall refute the model. The model, in general,is found to be consistent with both $CP$ conserving and $CP$ violating solutions.

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arXiv2021

Scalar Dark Matter in $A_4$ based texture one-zero neutrino mass model within Inverse Seesaw Mechanism

In this paper, we present a model based on $A_4$ discrete flavor symmetry implementing inverse and type-II seesaw mechanisms to have LHC accessible TeV scale right-handed neutrino mass and texture one-zero in the resulting Majorana neutrino mass matrix, respectively. We investigate neutrino and dark matter sectors of the model. Non-Abelian discrete $A_{4}$ symmetry spontaneously breaks into $Z_{2}$ subgroup and hence provide stable dark matter candidate. To constrain the Yukawa Lagrangian of our model, we imposed $Z'_2$, $Z_3$ and $Z_4$ cyclic symmetries in addition to the $A_4$ flavor symmetry. In this work we used the recently updated data on cosmological parameters from PLANCK 2018. For the dark matter candidate mass around 45 GeV-55 GeV, we obtain the mediator particle mass(right-handed neutrinos) ranging from 138 GeV to 155 GeV. The Yukawa couplings is found to be in the range 0.995-1 to have observed relic abundance of dark matter. We, further, obtain inverse ($X\equiv\frac{F^2n}{z^2}$) and type-II ($X^{'}\equiv f_1 v_{Δ_{1}}$) seesaw contributions to $0νββ$ decay amplitude $|M_{ee}|$, while model being consistent with low energy experimental constraints. In particular, we emphasize that type-II seesaw contribution to $|M_{ee}|$ is large as compared to inverse seesaw contribution for normally ordered(NO) neutrino masses.

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arXiv2021

Scotogenesis in Hybrid Textures of Neutrino Mass Matrix and Neutrinoless Double Beta Decay

We study the connection between dark matter (DM) and neutrinoless double beta ($0νββ$) decay in a scotogenic model with hybrid texture in the neutrino mass matrix. Characteristically, the framework allows to write all the non-zero elements of the mass matrix proportional to effective Majorana mass $\left|M_{ee}\right|$. The overall scale of the neutrino mass is found to be governed by non-zero $\left|M_{ee}\right|$. We have obtained interesting correlations of relic density of DM($Ωh^2$) with DM mass $M_1$ and $\left|M_{ee}\right|$. Using experimental value of DM relic density($Ωh^2$), the DM mass $M_1$, is found to be $\mathcal{O}$(1TeV) which is within reach of collider experiments. Specifically, for all five hybrid textures, the range of upper bound on DM mass $M_1$ is found to be ($2.27$-$5.31$)TeV. Another interesting feature of the model is the existence of lower bound on $|M_{ee}|$ for all allowed hybrid textures except texture $T_5$ which can be probed in current and future $0νββ$ decay experiments. With high sensitivities, these experiments shall establish the theoretical status of the proposed model. For example, the non-observation of $0νββ$ decay down to the sensitivity $\mathcal{O}(0.03)$eV will refute $T_3$ hybrid texture.

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arXiv2021

Broken Scaling Neutrino Mass Matrix and Leptogenesis based on A$_4$ Modular invariance

In this work, we have proposed a modular $A_4$ symmetric model of neutrino mass which, simultaneously, explains observed baryon asymmetry of the Universe(BAU). In minimal extension of the standard model(SM) with two right-handed neutrinos we work in a supersymmetric framework. At Type-I seesaw level, the model predicts scaling in the neutrino mass matrix. In order to have correct low energy phenomenology, we propose two possible scenarios of scale-breaking in the neutrino mass matrix emanating from Type-I seesaw. Scenario-1 is based on the dimension-5 Weinberg operator whereas scenario-2 implements Type-II seesaw via scalar triplet Higgs superfields($Δ,\barΔ$). Interestingly, the breaking patterns in both, otherwise dynamically different scenarios, are similar which can be attributed to the same charge assignments of superfields($Δ,\barΔ$) and the Higgs superfield $H_u$ under modular $A_4$ symmetry. The breaking is found to be proportional to the Yukawa coupling of modular weight 10($Y_{1,1'}^{10}$). We, further, investigates the predictions of the model under scenario-2 (Type-I+II) for neutrino mass, mixings and matter-antimatter asymmetry of the Universe. The model predicts normal hierarchical neutrino masses and provide a robust range ($0.05-0.08$)eV for sum of neutrino masses($\sum m_{i}$). Lepton number violating $0νββ$ decay amplitude($M_{ee}$) is obtained to lie in the range ($0.04-0.06$)eV. Future $0νββ$ decay experiments such as NEXT and nEXO shall pose crucial test for the model. Both $CP$ conserving and $CP$ violating solutions are allowed in the model. Interesting correlations are obtained, specially, between Yukawa couplings of modular weight 2 and complex modulus $τ$. The model exhibit consistent explanation of BAU for right-handed Majorana neutrino mass scale in the range ($(1-5)\times10^{13}$)GeV.

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arXiv2020

Non-Standard Interactions and Prospects for Studying Standard Parameter Degeneracies in DUNE and T2HKK

The future long baseline experiments such as DUNE and T2HKK have promising prospects to determine the neutrino mass hierarchy and measuring standard $CP$ phase $δ$. However, presence of possible non-standard interactions of neutrinos with matter may intricate this picture and is the subject matter of the present work. We have studied the standard parameter degeneracies in presence of non-standard interactions(NSI) with DUNE and T2HKK experiments. We examine the mass hierarchy degeneracy assuming (i) all NSI parameters to be non-zero and (ii) one NSI parameter($ε_{eμ}$) and its corresponding $CP$ phase($δ_{eμ}$) to be non-zero. We find that the later case is more appropriate to resolve mass hierarchy degeneracy with DUNE and T2HKK experiments due to relatively small uncertainties emanating from the NSI sector. We have, also, investigated the octant degeneracy with neutrino($ν_μ\rightarrowν_{e}$) and antineutrino($\barν_μ\rightarrow\barν_{e}$) mode separately. We find that to resolve this degeneracy the long baseline experiment with combination of neutrino and antineutrino mode is essential. Furthermore, we have considered DUNE in conjunction with T2HKK experiment to study $CP$ phase degeneracy due to standard($δ$) and non-standard($δ_{eμ}$) $CP$ phases. We find that DUNE and T2HKK, in conjunction, has more sensitivity for $CP$ violation effects(10$σ$ for true NH and 8.2$σ$ for true IH).

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arXiv2020

Magic neutrino mass model with broken $μ-τ$ symmetry and Leptogenesis

We investigate baryogenesis via leptogenesis in $A_4$ flavor model within the paradigm of type-I and II seesaw mechanism resulting in magic neutrino mass matrix with broken $μ-τ$ symmetry in a minimal scenario with two right-handed neutrinos(2RHN). Additional $Z_3$ cyclic symmetry is employed to constrain the Yukawa structure of model. The type-II seesaw terms play crucial role in generating non-degenerate neutrino masses and non-zero $θ_{13}$ and contribute in baryogenesis. In particular, after the spontaneous symmetry breaking, the Yukawa couplings $y_{Δ_1}$ and $y_{Δ_3}$ are responsible for the breaking of $μ-τ$ symmetry. The effective Majorana neutrino mass $|M_{ee}|$ is found to be well within the sensitivity reach of the $0νββ$ experiments, in particular, for inverted hierarchy. The model has imperative implication for inverted hierarchy, for example, the non-observation of this process at nEXO will rule out IH. The predicted baryon asymmetry is in good agreement with the observed baryon asymmetry for NH whereas IH is disallowed at 2.5$σ$ C.L..

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arXiv2019

Highly predictive and testable $A_{4}$ flavor model within type-I and II seesaw framework and associated phenomenology

We investigate neutrino mass model based on $A_4$ discrete flavor symmetry in type-I+II seesaw framework. The model has imperative predictions for neutrino masses, mixing and $CP$ violation testable in the current and upcoming neutrino oscillation experiments. The important predictions of the model are: normal hierarchy for neutrino masses, a higher octant for atmospheric angle ($θ_{23}>45^{o}$) and near-maximal Dirac-type $CP$ phase ($δ\approxπ/2$ or $3π/2$) at $3σ$ C. L.. These predictions are in consonance with the latest global-fit and results from Super-Kamiokande(SK), NO$ν$A and T2K. Also, one of the important feature of the model is the existence of a lower bound on effective Majorana mass, $|M_{ee}|\geq 0.047$eV(at 3$σ$) which corresponds to the lower part of the degenerate spectrum and is within the sensitivity reach of the neutrinoless double beta decay(0$νββ$) experiments.

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arXiv2018

Quark-lepton complementarity model based predictions for $θ_{23}^{PMNS}$ with neutrino mass hierarchy

After the successful investigation and confirmation of non zero $θ_{13}^{PMNS}$ by various experiments, we are standing at a square where we still encounter a number of issues, which are to be settled. In this paper, we have extended our recent work towards a precise prediction of the $θ_{23}^{PMNS}$ mixing angle, taking into account the neutrino mass hierarchy. We parameterize the non-trivial correlation between quark (CKM) and lepton (PMNS) mixing matrices in quark-lepton complementarity (QLC) model as $V_{c}= U_{CKM}. ψ. U_{PMNS}$, where $ψ$ is a diagonal phase matrix. Monte Carlo simulations are used to estimate the texture of $V_{c}$ and compare the results with the standard Tri-Bi-Maximal (TBM) and Bi-Maximal(BM) structures of neutrino mixing matrix. We have predicted the value of $θ_{23}^{PMNS} $ for normal and inverted neutrino mass hierarchies. The value of $θ_{23}^{PMNS}$ obtained for two cases are about $1.3σ$ away from each other, implying the better precision can give us a strong hint for the type of neutrino mass hierarchy.

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arXiv2018

Connecting Majorana phases to the Geometric Parameters of Majorana Unitarity Triangle in a model of Neutrino Mass Matrix

We have investigated a possible connection between the Majorana phases and geometric parameters of leptonic unitarity triangle(LUT) in two-texture zero neutrino mass matrix. Such analytical relations can, also, be obtained for other theoretical models viz. hybrid textures, neutrino mass matrix with vanishing minors and have profound implications for geometric description of $CP$ violation. As an example, we have considered two-texture zero neutrino mass model to obtain relation between Majorana phases and LUT parameters. In particular, we find that Majorana phases depend on only one of the three interior angles of LUT in each class of two-texture zero neutrino mass matrix. We have, also, constructed LUT for class $A$, $B$ and $C$ neutrino mass matrices. Non-vanishing areas and nontrivial orientations of these Majorana unitarity triangles indicate non-zero $CP$ violation as a generic feature of this class of mass models.

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arXiv2016

Probing Non-unitary $CP$ Violation effects in Neutrino Oscillation Experiments

In the present work, we have considered minimal unitarity violation(MUV) scheme, to obtain the general expression for $ν_μ\rightarrowν_τ$ oscillation probability, in vacuum. For this channel, we have investigated the sensitivities to non-unitary parameters $|ρ_{μτ}|$ and $ω_{μτ}$ with short baseline(SBL) experiments for normal as well as inverted hierarchical neutrino masses. We also check how the sensitivity to non-unitary parameters get modified for $θ_{23}$ above and below maximality. We find that the $3σ$ sensitivity towards $|ρ_{μτ}|$ is maximum for non-unitary phase $ω_{μτ}=0$, whereas it is minimum for $ω_{μτ}=\pmπ$ in case of normal hierarchy(NH). However, the sensitivity is minimum at $ω_{μτ}=0$ and maximum for $ω_{μτ}=\pmπ$ for inverted hierarchy(IH). We observe that for unitary $CP$ phase $δ=0$ and $δ=π/2$, the sensitivity to measure non-unitarity remains same in both the cases. We, also, explore wide range of $L/E$ to forecast, in principle, the possibilities to observe $CP$-violation due to unitary($δ$) and non-unitary($ω_{μτ}$) phases. We find that the both phases can be disentangled, in principle, from each other, for the $L/E$ range less than 200 km/GeV for $ν_μ\rightarrowν_τ$ channel.

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arXiv2016

Prospects for Reconstruction of Leptonic Unitarity Quadrangle and Neutrino Oscillation Experiments

After the observation of non-zero $θ_{13}$ the goal has shifted to observe $CP$ violation in the leptonic sector. Neutrino oscillation experiments can, directly, probe the Dirac $CP$ phases. Alternatively, one can measure $CP$ violation in the leptonic sector using Leptonic Unitarity Quadrangle(LUQ). The existence of Standard Model (SM) gauge singlets - sterile neutrinos - will provide additional sources of $CP$ violation. We investigate the connection between neutrino survival probability and rephasing invariants of the $4\times4$ neutrino mixing matrix. In general, LUQ contain eight geometrical parameters out of which five are independent. We obtain $CP$ asymmetry($P_{ν_f\rightarrowν_{f'}}-P_{\barν_f\rightarrow\barν_{f'}}$) in terms of these independent parameters of the LUQ and search for the possibilities of extracting information on these independent geometrical parameters in short baseline(SBL) and long baseline(LBL) experiments, thus, looking for constructing LUQ and possible measurement of $CP$ violation. We find that it is not possible to construct LUQ using data from LBL experiments because $CP$ asymmetry is sensitive to only three of the five independent parameters of LUQ. However, for SBL experiments, $CP$ asymmetry is found to be sensitive to all five independent parameters making it possible to construct LUQ and measure $CP$ violation.

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arXiv2012

Maximal CP-Violation in Neutrino Mass Matrix in light of the latest Daya Bay result on $θ_{13}$

The Daya Bay Collaboration (An et al) has recently proclaimed discovery of non-zero reactor angle, $θ_{13}$, $\sin^{2}2θ_{13}$=0.092$\pm$0.016(stat)$\pm$0.005(syst), at $5.2σ$ which is in conformity with the earlier observations of Abe et al, Adamson et al and Kerret et al last year. The discovery has immense implication for exploring CP-violation in the leptonic sector. In the present work, we examine CP-violation in Majorana neutrino mass matrix, in the basis where charged lepton mass matrix is diagonal, in which the ratio of elements are equal, also, termed as Strong Scaling Ans$\ddot{a}$tz (SSA). This Ans$\ddot{a}$tz has been known to explain the vanishing of $θ_{13}$ and predict inverted hierarchy (IH) for the neutrino masses. However, to generate a non-zero value of $θ_{13}$ consistent with Daya Bay result one has to deviate from SSA. This deviation will have important implications for CP-violation in the leptonic sector and is one of the issues addressed in the present work. CP is maximally violated because, for central value of $θ_{13}$ obtained from Daya Bay experiment, Dirac-type phase $|δ|\approx \fracπ{2}$, $\frac{3 π}{2}$ which corresponds to $|J_{CP}|\approx0.03$. We have, also, studied imperative implications for Majorana-type phases $α$, $β$ and effective neutrino mass, $M_{ee}$. The Majorana-type phases $α$, $β$ are found to be sharply constrained.

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arXiv2012

Four Zero Texture Fermion Mass Matrices in SO(10) GUT

We attempt the integration of the phenomenologically successful four zero texture of fermion mass matrices with the renormalizable SO(10) GUT. The resulting scenario is found to be highly predictive. Firstly, we examine the phenomenological implications of a class of the lepton mass matrices with parallel texture structures and obtain interesting constraints on the parameters of the charged lepton and the neutrino mass matrices. We combine these phenomenological constraints with the constraints obtained from SO(10) GUT to reduce the number of the free parameters and to further constrain the allowed ranges of the free parameters. The solar/atmospheric mixing angles obtained in this analysis are in fairly good agreement with the data.

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arXiv2011

Non-zero $θ_{13}$ and CP-violation in inverse neutrino mass matrix

The generic predictions of inverse Majorana neutrino mass matrix, $M_ν^{-1}$ with texture two zeros, in the basis where charged lepton mass matrix is diagonal, have been obtained for neutrino masses and mixings, especially, $θ_{13}$ and CP-violating phases. Such type of mass models are natural in the context of seesaw models with Dirac neutrino mass matrix, $M_{D}$, diagonal. Out of the fifteen possible texture two zeros patterns of the inverse neutrino mass matrix only seven are found to be compatible with the available data on neutrino masses and mixings including the latest $T\emph{2}K$ observation of non-zero $θ_{13}$. It is, also, found that $θ_{13}=0$ is disallowed in the mass models investigated in the present work. While the neutrino mass matrices of type I and II are found to be necessarily CP violating, type III is found to be CP-violating for a special case where $θ_{23}$ lie above maximality. The atmospheric mixing angle, $θ_{23}$ is found to dictate the possible hierarchies in type I and II neutrino mass models. For type III, additional information regarding $m_{ee}$ will be required to rule out the inverted hierarchy (IH). A maximal $θ_{23}$ is found to be disallowed in all types of texture two zero $M_ν^{-1}$ Ans$\ddot{a}$tz.

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arXiv2010

Leptogenesis in a Hybrid Texture Neutrino Mass Model

We investigate the CP asymmetry for a hybrid texture of the neutrino mass matrix predicted by $Q_8$ family symmetry in the context of the type-I seesaw mechanism and examine its consequences for leptogenesis. We, also, calculate the resulting Baryon Asymmetry of the Universe (BAU) for this texture.

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arXiv2010

Neutrino Mass Matrices with a Texture Zero and a Vanishing Minor

We study the implications of the simultaneous existence of a texture zero and a vanishing minor in the neutrino mass matrix. There are thirty six possible texture structures of this type, twenty one of which reduce to two texture zero cases which have, already, been extensively studied. Of the remaining fifteen textures only six are allowed by the current data. We examine the phenomenological implications of the allowed texture structures for Majorana type CP-violating phases, 1-3 mixing angle and Dirac type CP-violating phase. All these possible textures can be generated through the seesaw mechanism and realized in the framework of discrete abelian flavor symmetry. We present the symmetry realization of these texture structures.

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arXiv2010

Phenomenological Analysis of Hybrid Textures of Neutrinos

We present a comprehensive phenomenological analysis of the allowed hybrid textures of neutrinos. Out of a total of sixty hybrid textures with one equality between the elements of neutrino mass matrix and one texture zero only twenty three are found to be viable at 99% C.L. whereas the earlier analysis found fifty four to be viable. We examine the phenomenological implications of the allowed hybrid textures including Majorana type CP-violating phases, 1-3 mixing angle and Dirac type CP-violating phase, $δ$. We, also, obtain lower bound on effective Majorana mass for all the allowed hybrid textures.

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