arXiv subjects

Vishnudath K. N.

Publications and source records attributed to Vishnudath K. N..

14 recordsLinked to original sources

arXiv2026

Multi-component Dark Matter in a Novel Three-Loop Inverse Scotogenic Seesaw Model

We consider a model which provides an explanation of the origin of light neutrino masses, the baryon asymmetry of the Universe -- via leptogenesis -- and explains the observed dark matter relic abundance with several components. In this scenario, Majorana masses of the active neutrinos are produced by the inverse seesaw (ISS) mechanism with the lepton-number-violating mass parameter being dynamically generated at three loops with a novel topology. This model is based on an extension of the Standard Model gauge symmetry by a global $U(1)'$ and a discrete $\mathbb{Z}_2\otimes \mathbb{Z}_3$. The latter, which is responsible for the radiative origin of the ISS lepton-number-violating parameter, survives the spontaneous breaking of the global $U(1)'$ and, at the same time, ensures the stabilization of the dark sector. The lightest particles carrying non-trivial residual charges are stable, becoming potentially viable dark matter candidates. The model complies with bounds and constraints from neutrino data, collider and high-intensity charged lepton flavor-violating observables, as well as dark matter relic density and direct detection. To efficiently explore the model's high-dimensional parameter space and identify phenomenologically viable regions, we perform a global numerical scan using the MultiNest algorithm.

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arXiv2026

Two-loop neutrino mass model with modular $S_4$ symmetry

We propose a two-loop radiative neutrino mass model based on the modular $Γ_4 \simeq S_4$ flavour symmetry supplemented by a discrete $Z_3$ symmetry. After spontaneous modular symmetry breaking, a remnant $Z_2$ symmetry guarantees both the radiative origin of active neutrino masses and stabilizes dark matter candidates. The model successfully reproduces charged lepton masses and neutrino oscillation data for normal ordering. It also predicts observable rates for charged lepton flavour violation (LFV). Due to the singlet-doublet mixing the model provides a viable scalar dark matter candidate. A fermionic dark matter candidate, strongly linked to LFV, is also present. We identify parameter regions consistent with relic density, LFV constraints, and direct detection limits, providing testable benchmark configurations.

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arXiv2024

A common framework for fermion mass hierarchy, leptogenesis and dark matter

In this work, we explore an extension of the Standard Model designed to elucidate the fermion mass hierarchy, account for the dark matter relic abundance, and explain the observed matter-antimatter asymmetry in the universe. Beyond the Standard Model particle content, our model introduces additional scalars and fermions. Notably, the light active neutrinos and the first two generations of charged fermions acquire masses at the one-loop level. The model accommodates successful low-scale leptogenesis, permitting the mass of the decaying heavy right-handed neutrino to be as low as 10 TeV. We conduct a detailed analysis of the dark matter phenomenology and explore various interesting phenomenological implications. These include charged lepton flavor violation, muon and electron anomalous magnetic moments, constraints arising from electroweak precision observables, and implications for collider experiments.

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arXiv2024

Freeze-in production of sterile neutrino dark matter in a gauged U$(1)^\prime$ model with inverse seesaw

We consider a general, anomaly free U$(1)^\prime$ extension of the Standard Model (SM) where the neutrino mass is generated at the tree level via the inverse seesaw mechanism. The model contains three right handed neutrinos, three additional singlet fermions, one extra complex scalar and a neutral gauge boson $(Z^\prime)$. Instead of resorting to a specific $U(1)$ extension, we consider a class of models by taking the $U(1)^\prime$ charges of the scalars to be free parameters. Here, we assign one pair of the pseudo-Dirac degenerate sterile neutrinos as Dark Matter (DM) candidates which are produced by the freeze-in mechanism. Considering different mass regimes of the DM, $Z^\prime$ and reheating temperature, we obtain constraints on the $U(1)^\prime$ charges giving the correct relic abundance. We have also obtained constraints on $Z^\prime$ mass and coupling from consideration of relic density as well as high energy collider experiments like ATLAS in case of heavy $Z^\prime$ or in intensity and lifetime frontier experiments like DUNE, FASERs, and ILC beam dump which are looking for light $Z^\prime$. Additionally, in this model, the decay of pseudo-Dirac DM into active neutrinos can explain the 511 keV line observed by the INTEGRAL satellite.

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arXiv2024

Left-Right model with radiative double seesaw mechanism

We propose an extended Left-Right symmetric model with an additional global symmetry $U(1)_X$, which after spontaneous symmetry breaking collapses to a residual subgroup $\mathbb{Z}_2$, ensuring that the light active neutrino masses are generated via a double seesaw mechanism at two loop level, with the Dirac submatrix arising at one loop. It also guarantees one loop level masses for the SM charged fermions lighter than the top quark and protects Dark Matter (DM) candidates of the model. To the best of our knowledge our model has the first implementation of the radiative double seesaw mechanism with the Dirac submatrix generated at one loop level. We show that the model can successfully accommodate the observed pattern of SM fermion masses as well as mixings and is compatible with the constraints arising from the muon $g-2$ anomaly, neutrinoless double beta decay and DM.

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arXiv2024

Gravitational waves from a scotogenic two-loop neutrino mass model

We propose a framework to account for neutrino masses at the two-loop level. This mechanism introduces new scalars and Majorana fermions to the Standard Model. It is assumed the existence of a global $\mathrm{U(1)\times \mathcal{Z}_2}$ symmetry which after partial breaking provides the stability of the dark matter candidates of the theory. The rich structure of the potential allows for the possibility of first-order phase transitions (FOPTs) in the early Universe which can lead to the generation of primordial gravitational waves as one of the potentially observable signatures of this model. Taking into account relevant constraints from lepton flavour violation, neutrino physics as well as the trilinear Higgs couplings at next-to-leading order accuracy, we have found a wide range of possible FOPTs which are strong enough to be probed at the proposed gravitational-wave interferometer experiments such as LISA.

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arXiv2024

Phenomenology of 3-3-1 models with radiative inverse seesaw mechanism

We propose two models based on the $SU(3)_C \times SU(3)_L \times U(1)_X$ gauge symmetry, each incorporating distinct inverse seesaw mechanisms for generating neutrino masses at the radiative level. Therefore, neutrino masses are suppressed by the radiative nature of the mass generation mechanism, which occurs after the spontaneous breaking of the global lepton number symmetry. Both scenarios discussed here are characterized by the presence of vector-like charged leptons, which are involved in generating the masses of the Standard Model charged leptons. These additional vector-like fermions contribute to the anomalous magnetic moments of the electron and the muon. We perform a detailed analysis of the scalar sectors, show that these models can successfully accommodate the observed baryon asymmetry through resonant leptogenesis, and compute charged lepton flavor-violating decays, such as $μ\rightarrow e γ$. We discuss the constraints of the model arising from these processes and those associated the non-unitarity of the lepton mixing matrix.

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arXiv2023

Linear seesaw mechanism from dark sector

We propose a minimal model where a dark sector seeds neutrino mass generation radiatively within the linear seesaw mechanism. Neutrino masses are calculable, since tree-level contributions are forbidden by symmetry. They arise from spontaneous lepton number violation by a small Higgs triplet vacuum expectation value. Lepton flavour violating processes e.g. $μ\to eγ$ can be sizeable, despite the tiny neutrino masses. We comment also on dark-matter and collider implications.

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arXiv2022

Leptogenesis and eV scale sterile neutrino

We consider the minimal extended seesaw model which can accommodate an eV scale sterile neutrino. The scenario also includes three heavy right handed neutrinos in addition to the light sterile neutrino. In this model, the active-sterile mixing act as non-unitary parameters. If the values of these mixing angles are of $\mathcal{O}(0.1)$, the model introduces deviation of the PMNS matrix from unitarity to this order. We find that the oscillation data from various experiments imposes an upper bound on the lightest heavy neutrino mass scale as $\sim 10^{11}$ GeV in the context of this model. We study {\it vanilla} leptogenesis in this scheme, where the decay of the heavy right handed neutrinos in the early universe can give rise to the observed baryon asymmetry. Here, even though the eV scale sterile neutrino does not participate directly in leptogenesis, its effect is manifested through the non-unitary effects. We find that the parameter space that can give rise to successful leptogenesis is constrained by the bounds on the active-sterile mixing as obtained from the global analysis.

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arXiv2020

Implications of the Dark LMA solution and Fourth Sterile Neutrino for Neutrino-less Double Beta Decay

We analyze the effect of the Dark-large mixing angle (DLMA) solution on the effective Majorana mass ($m_{ββ}$) governing neutrino-less double beta decay ($0νββ$) in the presence of a sterile neutrino. We consider the 3+1 picture, comprising of one additional sterile neutrino. We have checked that the MSW resonance in the sun can take place in the DLMA parameter space in this scenario. Next we investigate how the values of the solar mixing angle $θ_{12}$ corresponding to the DLMA region alter the predictions of $m_{ββ}$ including a sterile neutrino in the analysis. We also compare our results with three generation cases for both standard large mixing angle (LMA) and DLMA. Additionally, we evaluate the discovery sensitivity of the future ${}^{136}Xe$ experiments in this context.

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arXiv2019

A New Sensitivity Goal for Neutrino-less Double Beta Decay Experiments

We study the implications of the Dark-LMA solution to the solar neutrino problem for neutrino-less double beta decay ($0νββ$ ). We show that while the predictions for the effective mass governing $0νββ$ remains unchanged for the inverted mass scheme, that for normal ordering becomes higher for the Dark-LMA parameter space and moves into the "desert region" between the two. This sets a new goal for sensitvity reach for the next generation experiments if no signal is found for the inverted ordering by the future search programmes.

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arXiv2019

Constraining a general U(1)$^\prime$ inverse seesaw model from vacuum stability, dark matter and collider

We consider a class of gauged $U(1)$ extensions of the Standard Model (SM), where the light neutrino masses are generated by an inverse seesaw mechanism. In addition to the three right handed neutrinos, we add three singlet fermions and demand an extra $Z_2$ symmetry under which, the third generations of both of the neutral fermions are odd, which in turn gives us a stable dark matter candidate. We express the $U(1)$ charges of all the fermions in terms of the U(1) charges of the standard model Higgs and the new complex scalar. We study the bounds on the parameters of the model from vacuum stability, perturbative unitarity, dark matter relic density and direct detection constraints. We also obtain the collider constraints on the $Z'$ mass and the $U(1)'$ gauge coupling. Finally we compare all the bounds on the $Z'$ mass versus the $U(1)'$ gauge coupling plane.

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arXiv2019

Constraining minimal Type-III Seesaw Model from naturalness, Lepton Flavor Violation and Electroweak Vacuum stability

We study the minimal type-III seesaw model in which we extend the SM by adding two $SU(2)_L$ triplet fermions with zero hypercharge to explain the origin of the non-zero neutrino masses. We show that the naturalness conditions and the limits from lepton flavor violating decays provide very stringent bounds on the model parameters along with the constraints from the stability/metastability of the electroweak vacuum. We perform a detailed analysis of the model parameter space including all the constraints for both normal as well as inverted hierarchies of the light neutrino masses. We find that most of the region that are allowed by lepton flavor violating decays and naturalness fall in the stable/metastable region depending on the values of the standard model parameters.

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arXiv2017

Electroweak vacuum stability in presence of singlet scalar dark matter in TeV scale seesaw models

We consider singlet extensions of the standard model, both in the fermion and the scalar sector, to account for the generation of neutrino mass at the TeV scale and the existence of dark matter respectively. For the neutrino sector we consider models with extra singlet fermions which can generate neutrino mass via the so called inverse or linear seesaw mechanism whereas a singlet scalar is introduced as the candidate for dark matter. We show that although these two sectors are disconnected at low energy, the coupling constants of both the sectors get correlated at high energy scale by the constraints coming from the perturbativity and stability/metastability of the electroweak vacuum. The singlet fermions try to destabilize the electroweak vacuum while the singlet scalar aids the stability. As an upshot, the electroweak vacuum may attain absolute stability even upto the Planck scale for suitable values of the parameters. We delineate the parameter space for the singlet fermion and the scalar couplings for which the electroweak vacuum remains stable/metastable and at the same time giving the correct relic density and neutrino masses and mixing angles as observed.

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