arXiv subjects

Sudhanwa Patra

Publications and source records attributed to Sudhanwa Patra.

At least 19 recordsLinked to original sources

arXiv2026

Probing Non-Holomorphic Modular $A_4$ Double Seesaw: Signatures in Neutrino Oscillation Experiments and Implications for Leptogenesis

We realize the double seesaw mechanism within a non-holomorphic modular $A_4$ framework by extending the Standard Model with three generations of right-handed neutrinos (RHNs), three left-handed sterile neutrino fields, and an $A_4$-singlet scalar. The modular construction forbids a bare Majorana mass term for the RHNs and realizes the hierarchy required for the double seesaw, with RHN masses induced through the heavier sterile neutrino sector. A comprehensive scan of the modular parameter space yields viable normal ordering solutions consistent with current neutrino oscillation data. We further examine their testability at DUNE, T2HK, and JUNO. DUNE and T2HK strongly probe the atmospheric mixing parameters and constrain the allowed model space, while JUNO provides complementary precision sensitivity to the solar mixing angle and mass-squared splitting. The oscillation compatible points also determine the induced RHN spectrum and complex Yukawa textures relevant for thermal leptogenesis. For a representative unflavored benchmark in the strong-washout regime, numerical Boltzmann evolution including decays and inverse decays yields $Y_{ΔB}\simeq8.11\times10^{-11}$, close to the observed baryon asymmetry. The allowed parameter space also admits an $N_1$-dominated two-flavor thermal leptogenesis realization with a hierarchical, non-resonant RHN spectrum. Our results establish the non-holomorphic modular $A_4$ double seesaw as a predictive framework linking low-energy neutrino phenomenology and thermal leptogenesis, with oscillation predictions directly testable at forthcoming precision neutrino experiments.

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arXiv2026

A Rotational Perturbative Correction to Democratic Neutrino Mixing and JUNO Compatibility

In this work, we revamp the democratic mixing matrix (DM) by adding a perturbation term such that the mixing angles derived from it are compatible with the NuFIT 6.1 and recent findings from the Jiangmen Underground Neutrino Observatory (JUNO). To do this, we have incorporated perturbation term in the elements of the mixing matrix such that it does not lose its unitarity. Thus, the democratic mixing matrix, once ruled out by the experimental evidences from T2K, Double Chooz, and Daya Bay, can be modified with rotational perturbation in the (1,2), (1,3), and (2,3) sectors and additional real parameters added in each element of DM. Finally, we analyze the allowed and disallowed textures in light of the JUNO findings.

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arXiv2026

Hyperonic compact stars with vector portal dark matter

The appearance of hyperons in the core of neutron stars generally softens the equation of state (EOS), posing a longstanding challenge to the existence of observed two-solar-mass compact stars. We investigate whether repulsive interactions mediated by a dark-sector vector portal can provide an additional source of high-density pressure and thereby modify the structure of hyperonic compact stars. The baryonic sector is described within the modified quark-meson coupling (MQMC) model, in which the octet baryons are treated as confined relativistic constituent-quark systems interacting self-consistently through the $σ$, $ω$, and $ρ$ fields within a mean field approximation. The dark sector consists of a fermionic dark matter coupled to baryonic matter through a neutral vector mediator $Z^\prime$, generating an additional repulsive contribution to the dense-matter EOS. We investigate the resulting equation of state, mass--radius relation, tidal deformability, and moment of inertia. The resulting mass--radius relations satisfy the observational bounds from massive pulsars, including PSR J0740 + 6620, with maximum neutron star masses reaching approximately $2 M_{\odot}$. The resulting changes in tidal and rotational observables provide additional avenues for testing the dark-sector interaction through multimessenger observations.

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arXiv2026

Probing T and CP Violation at DUNE and T2HK

We study the sensitivity of the DUNE and T2HK long-baseline experiments to time reversal (T) violation in neutrino oscillations. Rather than the conventional approach of exchanging initial and final neutrino flavors, we search for T violation through the $L$-dependence of the $ν_μ\to ν_e$ transition probability at fixed neutrino energy using neutrino data only. Within the standard three-flavour framework, we show that the DUNE and T2HK together can establish the presence of an $L$-odd component in the oscillation probability at up to $\sim 4σ$ significance, with the optimal sensitivity in the energy range $E_ν\in [0.68, 0.92]$ GeV. The second oscillation maximum of DUNE plays a crucial role in this analysis. We further show that DUNE is more sensitive to T violation that is running in neutrino-only mode, whereas T2HK provides better sensitivity in the conventional neutrino versus anti-neutrino comparison, making the two experiments complementary to each other in search of the CP phase $δ_{\rm CP}$.

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arXiv2026

Probing Leptophobic Dark Sectors via Gravitational Wave Signatures

We study a minimally extended version of the Standard Model where baryon number is gauged with a $U(1)_B$ symmetry. This model can be made anomaly-free by adding a set of additional fermions. The lightest component of these fermions behaves as a viable dark matter candidate. We show that the spontaneous breaking of $U(1)_B$ symmetry can produce gravitational waves via bubble dynamics resulting from a first-order phase transition, which can be detected in future gravitational wave experiments like LISA and ET. Such gravitational wave signatures can be used as a probe to constrain the model in future observations and complement dark matter and collider searches. We perform a random numerical scan of the parameter space and derive the viable region consistent with theoretical bounds from running of the coupling constants, current experimental bounds from dark matter experiments such as LUX-ZEPLIN and XENONnT and sensitive to future gravitational wave experiments. We find that dark matter with mass of 8 - 12 TeV is the most interesting to test in future gravitational wave as well as laboratory experiments. In the viable parameter space, the mass of the $Z'$ gauge boson associated with the $U(1)_B$ lies in the 16 - 24 TeV range, and the mass of the scalar associated with the symmetry breaking lies around 1 - 2.5 TeV scale. Recent results from LUX-ZEPLIN rules out mass scales below TeV in this model, while dark matter with mass larger than 12 TeV will not be sensitive to future GW experiments. Hence, the dark matter and mediator mass scales of interest are marginally accessible at current collider energies.

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arXiv2026

Probing mixed-state dark matter and flavor observables in a scalar-assisted baryonic gauge theory

We explore a {standard model} extension based on a local $U(1)_B$ symmetry, where a baryon-charged scalar mediates interactions between a fermionic dark matter candidate and {standard model} quarks. In this setup, the dark matter relic abundance is shaped not only by standard annihilation channels but also by additional coannihilation processes induced by a new scalar. The presence of this mediator provides a unified link between {dark sector} and flavor physics, yielding distinctive phenomenological consequences. We conduct a detailed study of dark matter phenomenology, emphasizing the role of the mass splitting between the dark matter particles and the scalar mediator in determining the efficiency of coannihilation. The parameter space is examined in light of existing constraints from cosmological observations, direct and indirect detection experiments, as well as the collider searches at the {\text{LHC}}. Our analysis shows that the extended scalar sector opens up viable regions of parameter space beyond those accessible in minimal $U(1)_B$ realizations, many of which are expected to be tested by forthcoming searches at {\text{XENONnT}} and {the \text{Cherenkov Telescope Array}}. Moreover, the model induces correlated signatures from flavor observables associated with the $b \to s $ transitions as well, serving as complementary tests of the underlying framework.

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arXiv2026

CP violating signal at DUNE in presence of nonstandard interactions and the role of second oscillation maxima

Neutrino oscillation among the three active neutrino flavors is well established and supported by experiments at diverse length scales and energy scales. It may be noted that five of the neutrino oscillation parameters in the three-flavor paradigm, namely the three mixing angles ($θ_{12}$, $θ_{13}$, $θ_{23}$) and the two mass-squared differences ($Δm^{2}_{21}$, $Δm^{2}_{31}$) are measured to a reasonable degree of precision. The three unknowns that are expected to be deciphered in the near future are the Dirac CP phase, $δ$, the neutrino mass ordering, and the octant of $θ_{23}$. The next generation of long baseline experiments, such as the Deep Underground Neutrino Experiment (DUNE), aims to resolve these unanswered questions. In the present work, by considering DUNE as an example, we assess the ability of long baseline experiments to extricate the intrinsic contribution from observables related to CP violation in scenarios with Standard Interaction (SI) and beyond. Additionally, we analyze the role of the second oscillation maximum in addressing the above mentioned questions. By carrying out event level and statistical analyses, we assess the potential of DUNE to probe CP violation effects both within and beyond the standard paradigm.

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arXiv2026

Neutron star with dark matter using vector portal

Compact astrophysical objects, such as neutron star, can provide a unique environment where the interplay between strongly interacting nuclear matter and dark matter (DM) can yield possible observable signatures. We investigate here the impact of fermionic DM interacting with nucleons via a vector mediator ($Z'$) portal inside neutron stars using the relativistic mean-field (RMF) framework. Unlike scalar portal DM models, which primarily modify the effective nucleon mass through scalar interactions, vector mediators (Z') introduce additional repulsive interactions that directly affect the baryonic chemical potential and the pressure of dense matter. We show that the precise measurements of neutron star properties, including the mass-radius relation and tidal deformability from gravitational wave observations, X-ray and radio observations of pulsars, can shed light on properties of DM. We study the gross structural properties of a neutron star using the Tolman-Oppenheimer-Volkoff (TOV) equations, employing an equation of state (EOS) for neutron star matter in the presence of vector portal-assisted DM. The resulting stellar configurations consistent with observational bounds from gravitational wave observations (GW170817) in LIGO/Virgo and X-ray observations of pulsar PSR J0030+0451 in NICER, are shown to constrain the vector portal DM parameters. It is observed that, while large portal mass can soften the EOS of the DM admixed neutron star matter, the light portal mass can make the EOS stiffer at large densities resulting in distinct mass-radius relation and the tidal deformability between the two scenarios. The vector portal DM scenario, with DM interaction with quarks via Z' vector boson, can establish a direct connection to terrestrial searches, including direct and indirect detection and collider searches for the Z' boson.

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arXiv2026

Radiative Dirac neutrino masses and dark matter in a $U(1)_{B-L}$ extended model

We study a $U(1)_{B-L}$ extension of the Standard Model (SM) in which Dirac neutrino masses are generated radiatively at the one-loop level through the exchange of new beyond the SM fields. This framework establishes a direct connection between neutrino mass generation and the dark sector, with the stability of the dark matter ensured by a residual discrete $Z_6$ symmetry arising from the spontaneous breaking of $U(1)_{B-L}$. We investigate the resulting charged lepton flavor violating processes and dark matter phenomenology, saturating relic observations and direct-detection constraints, and analyze the collider signatures of the dark sector at the Large Hadron Collider, its proposed high luminosity extension and at a future muon collider. We have identified excellent prospects for observing the considered dark matter candidates in these colliders, even with lower integrated luminosities than the proposed one.

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arXiv2026

Concurrence fill and mode distribution of entanglement in neutrino oscillation

In the framework of three flavor neutrino oscillation, we demonstrate that the measures of entanglement can be expressed in terms of experimentally accessible appearance and disappearance probabilities. We explicitly show here that the genuine tripartite entanglement measure, i.e., the tangle vanishes identically for all flavors signifying that three flavor neutrino system form a W-type entangled state. Further, we investigate alternative measures of tripartite entanglement like the partial tangle and the concurrence fill which capture the total sharing of entanglement beyond pairwise correlations. In terms of bipartite and bi-partitioned entanglement measures, we derive the symmetric invariant and the concurrence fill, which quantify the distributed entanglement completely expressible in terms of flavor transition probabilities. These entanglement measures display distinct energy dependent patterns across the oscillation window which can be experimentally accessible in the long baseline experiments like DUNE providing an alternative quantum information perspective on flavor evolution. We use GLobal Long Baseline Experiment Simulator (\textsf{GLoBES}) simulations within the DUNE set up to investigate these tripartite entanglement measures in terms of neutrino energy and the length of the baseline. It is observed that, at the point of maximal mixing, these measures show near maximal entanglement between the muon and the tau flavor modes establishing entanglement monogamy. Within the DUNE set up, the wide band of energy and expected higher sensitivity to CP-violation at second oscillation maximum provide a unique advantage to explore the quantum correlation effects across a broader energy window.

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arXiv2026

Non-Holomorphic $A_4$ Modular Symmetry in Type-I Seesaw: Implications for Neutrino Masses and Leptogenesis

We propose a minimal extension of the Standard Model with right-handed neutrinos, governed by a non-holomorphic $A_{4}$ modular flavor symmetry. Within this model framework, the light neutrino masses are generated via the popular type-I seesaw mechanism in which the structure of the Dirac neutrino Yukawa couplings is decided by nonholomorphic modular forms. Unlike conventional flavor models with ad hoc flavon fields, the structure of Dirac and Majorana mass matrices is entirely determined by a modulus parameter $τ$. We construct the predictive mass matrices for charged leptons, Dirac neutrinos, and right-handed Majorana neutrinos and show the compatibility with neutrino oscillation data by an appropriate choice of input model parameters. We present numerical analysis of two sets of benchmark points explaining neutrino masses while generating the correct amount of baryon asymmetry via thermal leptogenesis. We estimate numerically the values of CP-asymmetry and examine the evolution of the lepton asymmetry by studying Boltzman equations by considering both strong and washout regimes with CP-asymmetry parameter in the range $|\varepsilon_{1}| \sim 10^{-4}$--$10^{-8}$. The model predicts an effective Majorana mass in the few meV range, below current experimental bounds but within reach of next-generation $0νββ$ searches. The key feature of non-holomorphic $A_4$ modular symmetry naturally accommodates non-zero neutrino masses and mixings, minimizes the Yukawa arbitrariness, and establishes a direct connection between high-scale leptogenesis with low-energy neutrino observable parameters, thereby the model provides a testable link between neutrino flavor physics and cosmology.

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arXiv2026

Probing $0νββ$ and $μ\to eγ$ via Fully Determined Dirac Mass Terms in LRSM with Double Seesaw

Neutrinoless double beta decay ($0νββ$) and charged lepton flavor violation (cLFV) experiments provide promising avenues to probe new physics contributions from extended neutrino sectors in beyond Standard Model (BSM) scenarios. We consider a Left-Right Symmetric Model (LRSM) extended with three generations of sterile neutrinos to realize a double type-I seesaw mechanism for light neutrino mass generation. The double seesaw induces maximal lepton number violation in the right-handed sector and facilitates enhanced Majorana masses for right-handed neutrinos, thereby leading to their dominant contributions in both cLFV and $0νββ$ processes. We perform a comprehensive exploration of the parameter space for new-physics contributions to the cLFV decay $μ\to e γ$ and to $0νββ$, considering two different textures for the Dirac mass matrices: (i) a symmetry-motivated limit with $M_D \propto \mathbb{1}$, and (ii) a texture fully determined by the model framework. A detailed analysis of the common parameter regions accessible to current experiments like KamLAND-Zen and LEGEND-200, and upcoming experiments, such as MEG-II and LEGEND-1000, is presented, underscoring the phenomenological relevance of this framework. Our results aim to provide optimistic benchmarks for future searches targeting right-handed current-mediated neutrino interactions.

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arXiv2026

An $A_4$-Symmetric Double Seesaw for Neutrino Masses and Mixing in Light of JUNO results

We discuss a double seesaw mechanism for generating light neutrino masses within the Standard Model extensions that include both right-handed neutrinos and extra gauge-singlet sterile fermions. The flavour structure of the double seesaw framework is invoked by an $A_4$ discrete symmetry which yields predictive textures for the Dirac neutrino mass matrix $M_D$, the mixing matrix $M_{RS}$ connecting right-handed and sterile neutrinos, and the bare Majorana mass matrix $M_S$ for the sterile neutrinos. The interesting feature of the present framework is that the combination of the double seesaw mechanism and $A_4$ flavour alignments yields a leading-order TBM structure, corrected by a single rotation in the (1-3) sector. We also derive analytic expressions for the heavy sterile eigenvalues and for the resulting light neutrino masses, thereby clarifying the role of the symmetry in shaping the neutrino mass hierarchy. We further incorporate the most recent JUNO measurements, which improve the precision of the solar mixing angle $\sin^2θ_{12} \simeq 0.31$, along with updated constraints on $\sin^2θ_{13}$. We show that these results significantly restrict the allowed parameter space of the model. In particular, the observed value of $\sin^2θ_{12}$ constrains the magnitude of the (1--3) rotation and the phases associated with the $A_4$ flavon couplings, while the value of $\sin^2θ_{13}$ sharpens these restrictions further. Overall, the interplay between double seesaw dynamics, $A_4$ flavour symmetry, and the recent JUNO constraints yields a highly predictive framework for neutrino masses and mixings, offering a coherent explanation for the generation of light neutrino masses and testable predictions for future experiments.

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arXiv2025

Wave-particle duality and entanglement in neutrino oscillation

We investigate wave--particle--entanglement complementarity in three-flavor neutrino oscillations within a quantum information--theoretic framework. Treating neutrino flavor evolution as an open quantum system and explicitly accounting for detector--propagation correlations, we extend the conventional wave--particle duality relation to a triality relation involving predictability, visibility, and entanglement. Using reduced density matrices and I-concurrence as a quantitative measure of entanglement, we demonstrate that the total information content of the system satisfies the relation $\mathcal{P}^2 + \mathcal{V}^2 + \mathcal{E}^2 = 1$. While predictability and visibility exhibit the expected complementary behavior, we show that entanglement encodes additional wave-like information that is not captured by visibility alone. We apply our formalism to realistic long-baseline neutrino experiments, namely \textsf{DUNE} and \textsf{T2K}, and find that at the first oscillation maximum, a simultaneous characterization of the particle-like and wave-like nature of neutrinos becomes possible through the combined measurement of predictability and entanglement. Our results provide a unified operational interpretation of neutrino oscillations and highlight the role of quantum correlations in extending wave--particle duality to multipartite systems.

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arXiv2025

Analysis of neutrino oscillation parameters in the light on quantum entanglement

Numerous neutrino experiments have confirmed the phenomenon of neutrino oscillation, providing direct evidence of the quantum mechanical nature of neutrinos. In this work, we investigate the entanglement properties of neutrino flavor states within the framework of three-flavor neutrino oscillation using two major entanglement measures: entanglement of formation (EOF) and concurrence, utilizing the DUNE experimental setup. Our findings indicate that the maximally entangled state appears between $ν_μ$ and $ν_τ$ whereas, $ν_{e}$ behaves as a nearly separable state. To further explore the nature of bipartite entanglement, we introduce the concept of the monogamy of entanglement, which allows us to investigate the distinction between genuine three-flavor entanglement and bipartite entanglement. Our analysis confirms that the three-flavor neutrino system forms a bipartite entanglement structure, adhering to the Coffman-Kundu-Wootters (CKW) inequality. Additionally, we implement a minimization procedure to find the best-fit values of the oscillation parameters that correspond to the concurrence minima at the two specific energy points where the concurrence reaches its lowest values. Using these best-fit values, we probe three fundamental unknowns in neutrino oscillation: CP violation sensitivity, neutrino mass hierarchy, and the octant issue of $θ_{23}$, across two distinct energy points. Our results manifest that while the best-fit values obtained through concurrence minimization show slightly reduced sensitivity to CP violation compared to current best-fit values, they exhibit greater sensitivity to the mass hierarchy. Furthermore, the study reveals a maximal mixing angle for the atmospheric sector.

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arXiv2025

Dirac vs. Majorana Dark Matter Imprints on Neutron Star Observables

The fundamental character of a fermionic dark matter, whether it is a Dirac or Majorana particle remains a key unresolved issue whose answer would profoundly affect dark-sector phenomenology and detection strategies thereby motivates complementary probes across particle and astrophysical experiments. Compact stars, particularly neutron stars, offer unique astrophysical laboratories for probing such fundamental properties under extreme densities. The presence of a fermionic DM admixed with nuclear matter can modify the equation of state, thereby affecting observable quantities such as the mass-radius (M-R) relation and tidal deformability. In this work, we investigate how the intrinsic particle nature of fermionic DM influences neutron star structure. Within a relativistic mean-field framework extended by a scalar (or Higgs like) portal coupling between DM and nucleons, we construct self-consistent equation of states for both Dirac and Majorana cases and solve the Tolman-Oppenheimer-Volkoff equations to obtain stellar configurations. Owing to the difference in internal degrees of freedom, Dirac DM (four degrees of freedom) generally softens the equation of state more strongly than Majorana DM (two degrees of freedom), leading to smaller radii and lower maximum masses. We identify the parameter space consistent with current NICER and gravitational-wave constraints, highlighting the potential of compact-star observations to discriminate between Dirac and Majorana dark matter.

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arXiv2025

T versus CP effects in DUNE and T2HK

Time reversal (T) symmetry violations in neutrino oscillations imply the presence of an $L$-odd component in the transition probability at fixed neutrino energy, with $L$ denoting the distance between neutrino source and detector. Within the standard three-flavour framework, we show that the combination of the transition probabilities determined at the DUNE and T2HK experiments can establish the presence of an $L$-odd component, and therefore provide sensitivity to T violation, up to $4σ$ significance. The optimal neutrino energy window is from 0.68 to 0.92 GeV, and therefore a crucial role is played by the low-energy part of the DUNE event spectrum covering the second oscillation maximum. We compare the sensitivity to T violation based on this energy range using neutrino data only with the more traditional search for charge-parity (CP) violation based on the comparison of neutrino versus anti-neutrino beam data. We show that for DUNE it is advantageous to run in neutrino mode only, i.e., searching for T violating effects, whereas T2HK is more sensitive to CP violation, comparing neutrino and anti-neutrino data. Hence, the two experiments offer complementary methods to determine the complex phase in the PMNS mixing matrix.

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arXiv2025

Model-independent search for T violation with T2HK and DUNE

We consider the time reversal (T) transformation in neutrino oscillations in a model-independent way by comparing the observed transition probabilities at two different baselines at the same neutrino energy. We show that, under modest model assumptions, if the transition probability $P_{ν_μ\toν_e}$ around $E_ν\simeq 0.86$ GeV measured at DUNE is smaller than the one at T2HK the T symmetry has to be violated. Experimental requirements needed to achieve good sensitivity to this test for T violation are to obtain enough statistics at DUNE for $E_ν\lesssim 1$ GeV (around the 2nd oscillation maximum), good energy resolution (better than 10%), and near-detector measurements with a precision of order 1% or better.

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