arXiv subjects

Surender Verma

Publications and source records attributed to Surender Verma.

At least 19 recordsLinked to original sources

arXiv2026

Radiative Lifting of $\mathbb{Z}_3$ Domain-Wall Degeneracy in a Type-III Seesaw Model: Implications for Leptogenesis and Gravitational Waves

In this work, we study a $\mathbb{Z}_3$-symmetric extension of the Standard Model with three hyperchargeless $SU(2)_L$ fermion triplets responsible for neutrino mass generation $\textit{via}$ the Type-III seesaw mechanism together with a complex scalar singlet $\chi$ whose vacuum expectation value spontaneously breaks the $\mathbb{Z}_3$ symmetry. Radiative corrections induced by the Yukawa interactions between the $SU(2)_L$ fermion triplets and the complex scalar singlet $\chi$ generate a Coleman-Weinberg vacuum bias that lifts the degeneracy among the $\mathbb{Z}_3$ vacua, leading to the annihilation of unstable domain-walls. Consequently, the degeneracy among the $\mathbb{Z}_3$ vacua is lifted radiatively through the Coleman-Weinberg effective potential, generating a dynamical bias term that triggers the annihilation of unstable domain walls. We perform a numerical analysis consistent with current neutrino oscillation data and identify viable regions of parameter space accommodating the observed neutrino masses and leptonic mixing parameters. The observed baryon asymmetry of the Universe is generated through thermal leptogenesis $\textit{via}$ the out-of-equilibrium decay of the lightest fermion triplet for masses around $\mathcal{O}(10^{9})\,\mathrm{GeV}$, consistent with the Type-III seesaw framework. Depending on the choice of model parameters, the predicted gravitational-wave spectrum can fall within the sensitivity reach of future space-based and ground-based gravitational-wave detectors. Our framework therefore establishes a correlation between neutrino mass generation, leptogenesis, radiative domain-wall instability, and gravitational-wave phenomenology.

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arXiv2026

Reconciling TM$_2$ Mixing with LMA and Dark-LMA Data based on Minimal Corrections from Charged-Lepton Sector

Motivated by the increasing precision of neutrino oscillation data, we study the corrections to the TM$_2$ neutrino mixing framework, emanating from $(1,2)$ sector of the charged lepton, for both the standard LMA and dark-LMA solutions. We employ the Wolfenstein parameterization of the charged-lepton mixing matrix, characterized by two additional parameters $(\lambda,\delta)$, which effectively reconciles the TM$_2$ neutrino-mixing predictions with current oscillation data. For the LMA solution, the allowed ranges are $0.1 \lesssim \lambda \lesssim 0.33$ and $\delta \in (20^\circ\!-\!90^\circ)\oplus(270^\circ\!-\!340^\circ)$, while the dark-LMA case requires $\lambda>0.24$ and $125^\circ<\delta<235^\circ$. Interestingly, for LMA case, the upper bound $\lambda \le 0.33$ is found to be dictated by the atmospheric mixing angle $\theta_{23}$. The model predicts sizeable CP violation, with $|J_{CP}|$ reaching values as large as $0.13$. We, also, analyze the effective Majorana mass parameter $m_{ee}$ relevant for neutrinoless double beta decay. The inverted hierarchy region lies within the sensitivity of future experiments for both solutions, whereas only part of the normal hierarchy region can be tested.

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arXiv2026

Implications of the First JUNO Results for Dirac Neutrino Texture Zeros

Motivated by the first oscillation results from JUNO, we study the phenomenological viability of texture zeros in the Dirac neutrino mass matrix. The improved precision on the solar mixing angle $\sin^2{\theta_{12}}$ and the solar mass-squared difference $\Delta m_{21}^2$ provide a stringent probe for scrutinizing predictive texture zero frameworks. We perform a systematic scan of the allowed parameter space for two-zero textures, identifying sharp correlations among oscillation observables arising from the reduced parameter space. Our analysis reveals that current JUNO measurements impose stringent constraints on the viable texture structures. In particular, although textures $C$, $A_2$, and $A_1$ were previously viable, current JUNO data strongly disfavor $C$, leaving only textures $A_2$ and $A_1$ compatible with the data. These findings underscore the remarkable sensitivity of Dirac texture zero scenarios to the solar sector.

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arXiv2026

Phenomenology of Vanishing Effective Majorana Mass with a Sterile Neutrino under Cosmological and JUNO Constraints

In the present work we investigate the phenomenological implications of a vanishing effective Majorana neutrino mass within a $3+1$ neutrino framework adding a eV-scale sterile neutrino beside three active neutrino states in light of latest cosmology driven bounds on sum of neutrino masses ($\sum_{i}m_i$). We explore the parameter space where the destructive interference between active and sterile states leads to vanishing amplitude, $M_{ee}$, of neutrinoless double beta ($0\nu\beta\beta$) decay. The allowed parameter space has been identified and predictions have been obtained taking into account the latest Planck and DESI+CMB bound on $\sum_{i}m_i$. We find that these bounds restrict the sterile mixing angle $\theta_{14}$ and the lightest active neutrino mass. Furthermore, we incorporate the refined precision data from JUNO experiment regarding solar oscillation parameters ($\theta_{12}, \Delta m_{21}^2$). We find that the sterile neutrino parameters like $\theta_{14}$ may not be sensitive to the JUNO precision measurements as the constraint imposed by precise $\theta_{12}$ is washed out by new cancellations driven through additional CP violating phases leading to vanishing $|M_{ee}|$.

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arXiv2026

Tri-Resonant Leptogenesis in a Non-Holomorphic Modular A$_4$ Scotogenic Model

We investigate low-scale baryogenesis \textit{via} tri-resonant leptogenesis within the scotogenic model with a scalar dark matter embedded in non-holomorphic modular $A_4$ symmetry framework. The model naturally accommodates three nearly degenerate right-handed (RH) neutrinos when they are assigned to the triplet representation of $A_4$. The near degeneracy originates from treating the symmetric contribution to the Majorana mass matrix, arising from the $\mathbf{3}\otimes\mathbf{3}$ decomposition of $A_4$, as a small perturbation to the dominant singlet contribution. Generalized CP (gCP) symmetry is imposed in the model, rendering the complex modulus $\tau$ as the sole source of CP violation. In particular, for the inverted hierarchy (IH), the predicted $3\sigma$ range of $\theta_{23}$ lies in the lower octant close to maximal value while CP phase $\delta_{\mathrm{CP}}$ and the Majorana phase $\alpha_{21}$ are predicted to lie close to $0^\circ$ or $360^\circ$. Also, in this case, predicted values of $m_{ee}$ and $\sum_i m_i$ can be tested and constrained by future neutrinoless double beta decay $(0\nu\beta\beta)$ experiments, as well as by cosmological observations, particularly DESI+BAO and Planck data. In fact DESI+BAO disallows IH in the model. We further show that successful baryogenesis can be achieved for both normal hierarchy (NH) and inverted hierarchy (IH) of light neutrino masses with RH neutrino masses as low as $537~\mathrm{GeV}$ rendering this scenario experimentally testable. For NH, RH neutrino mass degeneracy of $\mathcal{O}(10^{-7}\!-\!10^{-6})$ is required, while for IH a stronger degeneracy of $\mathcal{O}(10^{-8})$ is needed. Remarkably, in the NH case, successful baryogenesis can occur even in the deep washout regime with decay parameters of $\mathcal{O}(10^{5})$ owing to the tri-resonant enhancement of the CP asymmetry and the inclusion of flavor effects.

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arXiv2026

Dark-Portal Leptogenesis in a Non-Holomorphic Modular Scoto-Seesaw Model

This work explores the neutrino phenomenology of the scotoseesaw model under non-holomorphic $A_4$ modular flavor symmetry providing a non-SUSY framework for realization of the modular symmetry. To prevent mixing between the beyond standard model fields associated with the tree and loop-level neutrino mass contributions, we assign even and odd modular weights to these sectors, respectively. The physical allowed ranges of oscillation parameters are used to identify the viable region of modulus parameter $\tau$ in its fundamental domain. With the complex modulus $\tau$ serving as the unique source of CP violation (all other parameters are real) the framework realizes successful low-scale leptogenesis through CP-violating decays of the lightest right-handed neutrino into Standard Model leptons and the Higgs boson. The requisite CP asymmetry arises from one-loop diagrams involving dark-sector states, obviating the need for degenerate mass spectra and thereby circumventing the usual resonant leptogenesis mechanism. The observation of a long-lived charged particle ($\eta^{\pm}$) in collider experiments would offer compelling evidence for the inert scalar sector of the model and provide a crucial experimental hint on the dark-sector assisted generation of neutrino masses and leptogenesis.

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arXiv2025

Type-III Seesaw in Non-Holomorphic Modular Symmetry and Leptogenesis

Recently, Qu and Ding, have proposed a formalism where modular invariance is extended to non-supersymmetric scenario considering Yukawa couplings as non-holomorphic functions of modules field $\tau$. Adopting this formalism in this work, we propose a Type-III seesaw model as a unified framework to explain lepton masses and mixing and baryogenesis via leptogenesis. $\chi^2$ analysis is performed to fit the neutrino oscillation data from NuFIT~6.0 leading to a normal hierarchical pattern of neutrino masses and constrained $CP$ phases. Furthermore, we analyze the generation of the observed baryon asymmetry of the Universe via thermal leptogenesis where the decays of the lightest fermion triplet $\Sigma_1$ into lepton-Higgs final states produce a $CP$ asymmetry $\varepsilon_{CP}$. The complex modules $\tau$ is responsible for the $CP$ asymmetry produced during leptogenesis. The washout processes dominated by gauge scatterings and inverse decays are studied through the full set of Boltzmann equations. The resulting $B-L$ asymmetry, $Y_{B-L}\sim 10^{-9}$ successfully reproduces the baryon-to-photon ratio demonstrating the model's capability to link low-energy neutrino data with the baryogenesis. The strong gauge-mediated washout of fermion triplets necessitates a leptogenesis scale of $\mathcal{O}(10^{12}\,\mathrm{GeV})$ ensuring compatibility with both the Davidson-Ibarra bound and the thermal history of the Universe. Future pursuits remain open to the exploration of novel avenues aimed at lowering the energy scale associated with leptogenesis.

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arXiv2025

Dark Matter and Collider Phenomenology in Radiative Type-III Seesaw Model with Two Inert Doublets

We investigate a minimal Type-III scotogenic model featuring two inert scalar doublets and a hyperchargeless triplet fermion. The scalar sector, in addition to the Standard Model Higgs, includes a rich spectrum of dark scalars comprising two CP-even, two CP-odd, and two charged states. This framework gives rise to two viable dark matter candidates: the lightest CP-even dark scalar and the neutral component of the triplet fermion. We perform a comprehensive analysis of both dark matter scenarios, carefully examining their viability under the umbrella of theoretical consistency conditions and experimental constraints. Beyond the conventional collider signatures anticipated in the Type-III scotogenic model with a single inert doublet, our extended framework predicts distinctive and novel signatures.

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arXiv2025

Neutrino Mass Matrix with broken Scaling in light of LMA and Dark-LMA Solutions

In the present work we have investigated some patterns of broken ``scaling" ansatz of the neutrino mass matrix. The scaling neutrino mass matrix is disallowed by the current neutrino oscillation data as, among others, it predicts vanishing reactor angle ($\theta_{13}=0$). We study its possible breaking scenarios in light of the large mixing angle (LMA) and Dark-LMA solutions suggested by current neutrino oscillation data. The normal hierarchical neutrino mass spectrum is ruled out in all three possible breaking patterns. Also, one of the interesting features of these breaking scenarios is the interplay between $\theta_{23}$-octant and possible CP violation. We find that the model allows maximal CP violation for $\theta_{23}$ above $6\%$ of its maximal value which, interestingly, is close to its current best-fit value for inverted hierarchical neutrino masses. We have, also, investigated the implications for effective Majorana neutrino mass parameter $|M_{ee}|$ for allowed breaking patterns. The correlation behavior of Majorana CP phases, which can be probed in $0\nu\beta\beta$ decay experiments, is found to have the capability of distinguishing LMA and Dark-LMA solutions.

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arXiv2025

Type-III Scotogenic Model: Inflation, Dark Matter and Collider Phenomenology

We investigate an extension of the Type-III scotogenic model by incorporating a real singlet scalar. This scalar plays a crucial role as the inflaton due to its non-minimal coupling with the Ricci scalar. The inflaton field subsequently decays into other particles within the Type-III scotogenic framework. In this framework, the inert scalar doublet and fermion triplet are crucial for neutrino mass generation and present strong candidates for 25\% energy budget or dark matter in the Universe. We study their relic abundance and potential for direct detection. Furthermore, we discuss possible observational signals that could be identified in future collider experiments.

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arXiv2024

Minimal Type-I Dirac seesaw and Leptogenesis under $A_{4}$ modular invariance

We present a Dirac mass model based on $A_{4}$ modular symmetry within Type-I seesaw framework. This extension of Standard Model requires three right-handed neutrinos and three heavy Dirac fermions superfields, all singlet under $SU(2)_{L}$ symmetry. The scalar sector is extended by the inclusion of a $SU(2)_{L}$ singlet superfield, $\chi$. Here, the modular symmetry plays a crucial role as the Yukawa couplings acquire modular forms, which are expressed in terms of Dedekind eta function $\eta(\tau)$. Therefore, the Yukawa couplings follow transformations akin to other matter fields, thereby obviating the necessity of additional flavon fields. The acquisition of $vev$ by complex modulus $\tau$ leads to the breaking of $A_{4}$ modular symmetry. We have obtained predictions on neutrino oscillation parameters, for example, the normal hierarchy for the neutrino mass spectrum. Furthermore, we find that heavy Dirac fermions, in our model, can decay to produce observed baryon asymmetry of the Universe through Dirac leptogenesis.

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arXiv2024

On Lepton Flavor Violation and Dark Matter in Scotogenic model with Trimaximal Mixing

We examine the Scotogenic model employing the TM$_2$ mixing matrix, $U_{\text{TM}_2}$, for neutrinos and parameterize the Yukawa coupling matrix $y$ based on the diagonalization condition for the neutrino mass matrix, $m_{\nu}$. Our investigation centers on analyzing the relic density of cold dark matter ($\Omega h^2$) and possible lepton flavor violation (LFV) in the model. In particular, we study coannihilation dynamics and LFV, in the model, considering various coannihilation scenarios including non-zero mass splitting between lightest sterile neutrinos. While analyzing, we have taken into consideration respective experimental constraints on $\Omega h^2$ and LFV alongside neutrino oscillation data. Our study reveals that in both normal and inverted hierarchy of neutrino masses, splitting between masses of $N_1$ and $N_2$ can be up to $\approx 15\%$ for the model to be in consonance with the above constraints. In the second part, we have extended the analysis incorporating extended magic symmetry in $m_\nu$ enabling us to completely determine Yukawa coupling matrix ($y$). We observe a notable exclusion of the effective Majorana mass $|m_{ee}|$ parameter space by cosmological bound on sum of neutrino masses, particularly in the normal hierarchy while inverted hierarchy scenario is excluded due to constraints coming from extended magic symmetry. These findings shed light on the interplay among the Scotogenic model, TM$_2$ mixing, and extended magic symmetry, offering insights into the permitted parameter space and hierarchy exclusion.

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arXiv2023

Low Scale Leptogenesis in Singlet-Triplet Scotogenic Model

The scotogenic model presents an elegant and succinct framework for elucidating the origin of tiny neutrino masses within the framework of the Standard Model, employing radiative corrections within the domain of the dark sector. We investigate the possibility of achieving low-scale leptogenesis in the singlet-triplet scotogenic model (STSM), where dark matter mediates neutrino mass generation. We initially considered a scenario involving two moderately hierarchical heavy fermions, N and $\Sigma$, wherein the lepton asymmetry is generated by the out-of-equilibrium decay of both particles. Our analysis indicates that the scale of leptogenesis in this scenario is similar to that of standard thermal leptogenesis and is approximately $M_{N,\Sigma}\sim 10^{9}$ GeV, which is comparable to the Type-I seesaw case. Further, we consider the case with three heavy fermions ($N_1$, $N_2$, and $\Sigma$) with the hierarchy $M_{N_{1}} < M_{\Sigma} \ll M_{N_{2}}$, which yields the lower bound on heavy fermions up to 3.1 TeV, therefore significantly reduce the scale of the leptogenesis up to TeV scale. The only prerequisite is suppression in the $N_{1}$ and $\Sigma$ Yukawa couplings, which causes suppressed washout effects and a small active neutrino mass of about $10^{-5}$ eV. This brings about the fascinating insight that experiments aiming to measure the absolute neutrino mass scale can test low-scale leptogenesis in the scotogenic model. Further, the hyperchargeless scalar triplet $\Omega$ provides an additional contribution to mass of the $W$-boson explaining CDF-II result.

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arXiv2023

Neutrino Phenomenology in a Model with Generalized CP symmetry within Type-I seesaw framework

We investigate the consequences of generalized CP (GCP) symmetry within the context of the two Higgs doublet model (2HDM), specifically focusing on the lepton sector. Utilizing the Type-I seesaw framework, we study an intriguing connection between the Dirac Yukawa couplings originating from both Higgs fields, leading to a reduction in the number of independent Yukawa couplings and simplifying the scalar and Yukawa sectors when compared to the general 2HDM. The CP3 constraint results in two right-handed neutrinos having equal masses and leads to a diagonal right-handed Majorana neutrino mass matrix. Notably, CP symmetry experiences a soft break due to the phase associated with the vacuum expectation value of the second Higgs doublet. The model aligns well with observed charged lepton masses and neutrino oscillation data, explaining both masses and mixing angles, and yields distinct predictions for normal and inverted neutrino mass hierarchies. It features a novel interplay between atmospheric mixing angle $\theta_{23}$ and neutrino mass hierarchy: the angle $\theta_{23}$ is below maximal for the normal hierarchy and above maximal for inverted hierarchy. Another interesting feature of the model is inherent CP violation for the inverted hierarchy.

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arXiv2022

Trimaximal Mixing and Extended Magic Symmetry in a Model of Neutrino Mass Matrix

The trimaximal mixing scheme (TM$_2$) results in \textit{``magic"} neutrino mass matrix ($M_\nu$) which is known to accommodate neutrino oscillation data. In this paper, we propose a phenomenological ansatz for $M_\nu$ by extending the magic symmetry that leads to further reduction in the number of free parameters, thereby, increasing the predictability of the model. The neutrino mixing parameters, effective Majorana mass $m_{ee}$ and $CP$ invariants ($J_{CP}, I_1,I_2$) are found to exhibit strong correlations for TM$_2$ mixing paradigm. One of the generic feature of the model is the requirement of non-maximal $\theta_{23}$ for possible $CP$ violation measurable in neutrino oscillation experiments. The observables $m_{ee}$ and sum of neutrino masses ($\sum m_i$) have imperative implications for yet unknown neutrino mass hierarchy. For inverted hierarchy, the lower bound on $m_{ee}>0.02$ eV, predicted by the model, is found to be within the sensitivity reach of the $0\nu\beta\beta$ decay experiments. Also, cosmological bound of $0.12$ eV on $\sum m_i$, at 95\% CL, refutes inverted hierarchy implying TM$_2$ with normal hierarchy as the only viable possibility in the model. We have, also, illustrated a scenario wherein such a construction of the neutrino mass matrix can be realized using $\Delta(54)$ symmetry in the framework of Type-I+II seesaw mechanism.

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arXiv2022

Muon ($g-2$) and W-boson mass Anomaly in a Model Based on $Z_4$ Symmetry with Vector like Fermion

The latest results of CDF-II collaboration show a discrepancy of $7\sigma$ with standard model expectations. There is, also, a $4.2\sigma$ discrepancy in the measurement of muon magnetic moment reported by Fermilab. We study the connection between neutrino masses, dark matter, muon ($g-2$) and W-boson mass anomaly within a single coherent framework based on $Z_{4}$ extension of the scotogenic model with vector like lepton (VLL). Neutrino masses are generated at one loop level. The inert doublet, also, provide a solution to W-boson mass anomaly through correction in oblique parameters $S$, $T$ and $U$. The coupling of VLL triplet $\psi_T$ to inert doublet $\eta$ provides positive contribution to muon anomalous magnetic moment. In the model, the VLL triplet provides a lepton portal to dark matter ($\eta_R^0$). The model predicts a lower bound $m_{ee}>0.025$ eV at 3$\sigma$, which is well within the sensitivity reach of the $0\nu\beta\beta$ decay experiments. The model explains muon anomalous magnetic moment $\Delta a_\mu$ for $1.3<y_\psi<2.8$ and mass of DM candidate in the range $152\text{ GeV}<M_{\eta_{R}^{0}}<195\text{ GeV}$. The explanation of W-boson mass anomaly, further, constrain the mass of DM candidate, $M_{\eta_{R}^{0}}$, in the range $154\text{ GeV}<M_{\eta_{R}^{0}}<174\text{ GeV}$.

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arXiv2022

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

In the framework of anomaly free $U(1)_{L_{\mu}-L_{\tau}}$ model, charged scalar fields give 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 the present 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, 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 $M_{Z_{\mu\tau}}$ in the range ($0.035$ GeV-$0.100$ GeV) and $g_{\mu\tau}\approx\mathcal{O}(10^{-4}$) 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 $U(1)_{L_{\mu}-L_{\tau}}$ Scotogenic Model Extended with Vector like Fermion

The latest results of anomalous muon magnetic moment at Fermilab show a discrepancy of 4.2 $\sigma$ between the Standard Model (SM) prediction and experimental value. In this work, we revisit $U(1)_{L_{\mu}-L_{\tau}}$ symmetry with in the paradigm of scotogenic model which explains muon ($g-2$) and neutrino mass generation, simultaneously. The mass of new gauge boson $M_{Z_{\mu\tau}}$ generated after the spontaneous symmetry breaking of $U(1)_{L_{\mu}-L_{\tau}}$ 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 $M_{Z_{\mu\tau}}-g_{\mu\tau}$ plane which explain the neutrino phenomenology. Region I is found to be consistent with muon neutrino trident (MNT) bound ($g_{\mu\tau}$ $\leq$ $10^{-3}$) to explain muon ($g-2$), however, region II violates it for mass range $M_{Z_{\mu\tau}}>300$ MeV. We, then, extend the minimal gauged scotogenic model by a vector like lepton (VLL) triplet $\psi_T$. The mixing of $\psi_T$ with inert scalar doublet $\eta$ leads to chirally enhanced positive contribution to muon anomalous magnetic moment independent of $Z_{\mu\tau}$ mass. Furthermore, we have, also, investigated the implication of the model for $0\nu\beta\beta$ decay and $CP$ violation. The non-observation of $0\nu\beta\beta$ 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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