arXiv subjects

Abinash Medhi

Publications and source records attributed to Abinash Medhi.

12 recordsLinked to original sources

arXiv2026

Resolving Lorentz-Violating New Physics at ESSnuSB Using High-Statistics Complementarity with T2HK

A primary objective for next-generation long-baseline neutrino facilities is the search for Planck-scale Lorentz Invariance Violation (LIV). In this work, we explore the capabilities of the proposed ESSnuSB and T2HK experiments to constrain isotropic, CPT-violating LIV parameters ($a_{αβ}$). The modifications to oscillation probabilities induced by these LIV parameters can introduce parameter degeneracies with the atmospheric mixing angle $θ_{23}$ and the Dirac CP-violating phase $δ_{CP}$, which can potentially result in incorrect determination of the said standard oscillation parameters if we do not account for LIV effects. Through detailed GLoBES simulations, we find that while the second-oscillation-maximum configuration of ESSnuSB yields good constraints on the exact phase of $δ_{CP}$, its intrinsic neutrino-antineutrino statistical asymmetry persistently leads to wrong octant fake solutions for $θ_{23}$. By synergizing ESSnuSB's 360 km and 540 km baselines with the complementary, high-statistics measurements from first-maximum configuration of the T2HK's 295 km baseline, we show that the degeneracies are resolved for most LIV parameters. Our analysis reflects how complementarity between ESSnuSB and T2HK provides an effective, matter-independent framework to break LIV-induced degeneracies and establish bounds on Planck-scale LIV physics.

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arXiv2026

Neutrino mass ordering from the next Galactic supernova at DUNE, HK, and JUNO

The next Galactic core-collapse supernova (CCSN) will offer a unique opportunity to determine the neutrino mass ordering. We focus on two observables: the electron neutrino ($ν_e$) neutronization burst and the rise-time of the electron antineutrino ($\barν_e$) flux during the accretion phase. The neutronization burst, a sharp $ν_e$ peak within $\sim 20$-$30$ ms, provides a clean and robust signature of mass ordering through its appearance or disappearance. During the accretion phase, the faster rise of heavy lepton flavor neutrinos ($ν_x$) leads to a distinct faster rise-time behavior of the oscillated $\barν_e$ signal, resulting in mass ordering discrimination. Using realistic CCSN simulations for multiple progenitor masses, we compute event rates and perform a statistical analysis for a Galactic ($10$~kpc) CCSN event at DUNE, Hyper-Kamiokande (HK), and JUNO detectors. The neutronization burst remains largely independent of SN hydrodynamic simulation models, with DUNE and HK achieving $\gtrsim 6σ$ and $\gtrsim 4σ$ sensitivity for normal (NO) to inverted ordering (IO) discrimination, respectively. However, the rise-time observable is prone to progenitor degeneracies. To mitigate this cumulative and ratio-based observables constructed at characteristic timescales ($20$ ms & $100$ ms) are used. The resulting confidence levels from the rise-time analysis to discriminate IO/NO in HK and JUNO are $\sim 5σ$ and $\sim 3σ$, respectively. Our results highlight the complementarity of detectors and observables, and demonstrate that combining neutronization burst and accretion phase information will be crucial for a definitive determination of the neutrino mass ordering in the next Galactic supernova.

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arXiv2026

Dark NSI & neutrino oscillations : probing via $δ_{CP}$ measurements at DUNE and T2HK

We investigate the possibility of neutrinos interacting with a scalar dark matter field and the resulting implications for neutrino oscillations in the long-baseline sector. As our Universe is predominantly composed of dark matter, neutrinos propagating over astrophysical and terrestrial baselines inevitably traverse a dark matter background. The coherent forward scattering of neutrinos in such a background induces a medium-dependent correction to the mass-squared term in the effective neutrino Hamiltonian having opposing signs for neutrinos and antineutrinos. We study how the elements of this correction matrix, arising from coherent forward scattering of neutrinos with scalar dark matter background referred to as dark non-standard interactions (dark NSI), modify neutrino oscillation probabilities. Furthermore, we also study the effect of the off-diagonal elements and the associated phases on the measurement of leptonic CP violating phase focusing on the upcoming long-baseline superbeam experiments DUNE and T2HK. We show that dark NSI can lead to substantial enhancement or suppression of CP-violation sensitivity, depending on the true values of the dark NSI phases $ϕ_{αβ}$. We further explored how the synergy of DUNE and T2HK can effectively mitigate the degeneracies due to the dark NSI phases, and can restore or even enhance the CP sensitivity as compared to the standard oscillation scenario.

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arXiv2025

Constraining and Resolving Lorentz-Violating New Physics at ESSnuSB Using Complementarity with DUNE

We examine the sensitivity of the ESSnuSB and DUNE long-baseline neutrino experiments to isotropic, CPT-violating Lorentz Invariance Violation (LIV). Using detailed simulations for the 360 km and 540 km ESSnuSB baselines and the 1300 km DUNE setup, we assess how LIV parameters influence oscillation probabilities, event spectra, and degeneracies among oscillation parameters. We find that LIV-induced modifications can closely mimic variations in $θ_{23}$ and $δ_{\rm CP}$, potentially leading to incorrect determination of the atmospheric mixing angle octant and the leptonic CP phase if LIV effects are not accounted for. Although combining the two ESSnuSB baselines improves overall sensitivity, it does not fully remove these degeneracies. In contrast, a joint ESSnuSB+DUNE analysis benefiting from the synergy between second-maximum sensitivity at ESSnuSB and first-maximum, matter-enhanced sensitivity at DUNE can successfully resolve all these degeneracies and can yield significantly stronger constraints on all the LIV parameters. The results presented here highlights the essential role of multi-baseline, multi-energy experimental strategies to probe Planck-suppressed Lorentz-violating new physics.

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arXiv2024

Neutrino mass ordering sensitivities at DUNE, HK and KNO in presence of scalar NSI

The limitations of the Standard Model in explaining neutrino masses and neutrino mixing lead to the exploration of frameworks beyond the Standard Model (BSM). The possibility of neutrinos interacting with fermions via a scalar mediator is one of the interesting prospects. The study of neutrino non-standard interactions (NSI) is a well-motivated phenomenological scenario to explore new physics beyond the Standard Model. These new interactions may alter the standard neutrino oscillation probabilities, potentially leading to observable effects in experiments. It also allows for the exploration of absolute neutrino masses via oscillation experiments. It can modify the oscillation probabilities, which in turn can affect the physics sensitivities in long-baseline experiments. The linear scaling of the effects of scalar NSI with matter density also motivates its exploration in long-baseline (LBL) experiments. We will present our study on the impact of a scalar-mediated NSI on the mass ordering (MO) sensitivities of three long-baseline neutrino experiments, i.e., DUNE, HK and KNO. We study the impact on MO sensitivities at these experiments assuming that scalar NSI parameters are present in nature and are known from other non-LBL experiments. The presence of scalar NSI can notably impact the MO sensitivities of these experiments. Furthermore, we analyze the potential synergy by combining data from DUNE with HK and HK+KNO, thereby exploring a broader parameter space.

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arXiv2024

Scalar NSI: A unique tool for constraining absolute neutrino masses via $ν$-oscillations

In the standard interaction scenario, a direct measurement of absolute neutrino masses via neutrino oscillations is not feasible, as the oscillations depend only on the mass-squared differences. However, scalar non-standard interactions (SNSI) can introduce sub-dominant terms in the neutrino oscillation Hamiltonian that can directly affect the neutrino mass matrix, thereby making SNSI a unique tool for neutrino mass measurements. In this work, for the first time, we constrain the absolute masses of neutrinos by probing SNSI. We have explored the constraints on the lightest neutrino mass with different choices of $δ_{CP}$ and $θ_{23}$ for both neutrino mass hierarchies. We show that a bound on the neutrino mass can be induced in the presence of SNSI at DUNE. We find that the lightest neutrino mass can be constrained with $η_{ττ}$ for normal mass hierarchy irrespective of the octant of $θ_{23}$ and the value of the CP phase $δ_{CP}$. This study suggests that SNSI can serve as an interesting avenue to constrain the absolute neutrino masses in long-baseline neutrino experiments via neutrino oscillations.

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arXiv2024

Neutrino Oscillations in Presence of Diagonal Elements of Scalar NSI: An Analytic Approach

Scalar Non-Standard Interactions (SNSI) in neutrinos can arise when a scalar mediator couples to both neutrinos and standard model fermions. This beyond the Standard Model (BSM) scenario is particularly interesting as the SNSI contribution appears as a density-dependent perturbation to the neutrino mass, rather than appearing as a matter-induced potential, and the neutrino oscillation probabilities uniquely depend on the absolute neutrino masses. In this work, we show the complex dependence of the SNSI contributions on the neutrino masses and discuss how the mass of the lightest neutrino would regulate any possible SNSI contribution in both mass ordering scenarios. We derive the analytic expressions for neutrino oscillation probabilities, employing the Cayley-Hamilton theorem, in the presence of diagonal elements of SNSI. The expressions are compact and shows explicit dependence on matter effects and the absolute neutrino masses. The analytic expressions calculated here allow us to obtain the dependence of the SNSI contribution on mass terms of the form $m_1 + m_2$, $m_2 - m_1$, $m_1c_{12}^2 + m_2s_{12}^2,$ $ m_1s_{12}^2 + m_2c_{12}^2$, and $m_3$. We then explore the non-trivial impact of neutrino mass ordering on the SNSI contribution. The dependence of the SNSI contribution on the 3$ν$ parameters is then thoroughly explored using our analytic expressions.

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arXiv2024

Impact of scalar NSI on the neutrino mass ordering sensitivity at DUNE, HK and KNO

The study of neutrino non-standard interactions (NSI) is a well-motivated phenomenological scenario to explore new physics beyond the Standard Model. The possible scalar coupling of neutrinos ($ν$) with matter is one of such new physics scenarios that appears as a sub-dominant effect that can impact the $ν$-oscillations in matter. The presence of scalar NSI introduces an additional contribution directly to the $ν$-mass matrix in the interaction Hamiltonian and subsequently to the $ν$-oscillations. This indicates that scalar NSI may have a significant impact on measurements related to $ν$-oscillations e.g. leptonic CP phase $(δ_{CP})$, $θ_{23}$ octant and neutrino mass ordering (MO). The linear scaling of the effects of scalar NSI with matter density also motivates its exploration in long-baseline (LBL) experiments. In this paper, we study the impact of a scalar-mediated NSI on the MO sensitivity of DUNE, HK and HK+KNO, which are upcoming LBL experiments. We study the impact on MO sensitivities at these experiments assuming that scalar NSI parameters are present in nature and is known from other non-LBL experiments. We observe that the presence of diagonal scalar NSI elements can significantly affect the $ν$-mass ordering sensitivities. We then also combine the data from DUNE with HK and HK+KNO to explore possible synergy among these experiments in a wider parameter space. We also observe a significant enhancement in the MO sensitivities for the combined analysis.

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arXiv2024

The Sensitivity of DUNE in Presence of Off-Diagonal Scalar NSI Parameters

Scalar non-standard interactions (NSI) presents an exciting pathway for probing potential new physics that extends beyond the Standard Model (BSM). The scalar coupling of neutrinos with matter can appear as a sub-dominant effect that can impact the neutrino oscillation probabilities. The uniqueness of these interactions is that it can directly affect the neutrino mass matrix. This makes oscillations sensitive to the absolute neutrino mass. The effects of scalar NSI scales linearly with matter density which motivates its exploration in long-baseline sector. The presence of scalar NSI can influence the key measurements in the field of neutrino physics, including the precise determination of the leptonic CP phase ($δ_{CP}$), neutrino mass ordering and the octant of $θ_{23}$. The precise determination of $δ_{CP}$ is one of the major goals of DUNE, which is an upcoming long-baseline experiment. A better understanding of the impact of scalar NSI on CP measurement sensitivities is crucial for accurate interpretation of $δ_{CP}$ phase. In this work, we have explored the impact of the complex off-diagonal scalar NSI elements $η_{αβ}$ and their associated phases $ϕ_{αβ}$ on the CP-measurement sensitivities at DUNE. We have explored the impact of the neutrino mass scale on these sensitivities. We look for constraining these off-diagonal elements for different neutrino mass scales. We also explore their correlation with $δ_{CP}$, investigating potential degeneracies that can arise due to additional phases. We also perform a correlation study among different scalar NSI elements. We show that the inclusion of the complex scalar NSI elements can significantly modify the CP phase measurements.

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arXiv2023

Investigating the effects of Lorentz Invariance Violation on the CP-sensitivities of the Deep Underground Neutrino Experiment

The neutrino oscillations offer great potential for probing new physics effects beyond the Standard Model. Any additional effect on neutrino oscillations can help understand the nature of these non-standard effects. The violation of fundamental symmetries may appear as new physics effects in various neutrino experiments. Lorentz symmetry is one such fundamental symmetry in nature, the violation of which implies a breakdown of space-time symmetry. The Lorentz Invariance Violation (LIV) is intrinsic in nature and its effects exist even in a vacuum. Neutrinos can be an intriguing probe for exploring such violations of Lorentz symmetry. The effect of violation of Lorentz Invariance can be explored through the impact on the neutrino oscillation probabilities. The effect of LIV is treated as a perturbation to the standard neutrino Hamiltonian considering the Standard Model Extension (SME) framework. In this work, we have probed the effect of LIV on the neutrino oscillation measurements considering the Deep Underground Neutrino Experiment (DUNE) as a case study. The inclusion of LIV affects various neutrino oscillation parameters as it modifies the standard neutrino oscillation probabilities. We looked into the capability of DUNE in constraining the LIV parameters and then explored the impact of CPT-violating LIV terms on the mass-induced neutrino oscillation probabilities. We have also probed the influence of LIV parameters on the CP-measurement sensitivity at DUNE.

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arXiv2023

Imprints of scalar NSI on the CP-violation sensitivity using synergy among DUNE, T2HK and T2HKK

The Non-Standard Interactions (NSIs) are subdominant effects, often appearing in various extensions of SM, which may impact the neutrino oscillations through matter. It is important and interesting to explore the impact of NSIs in the ongoing and upcoming precise neutrino oscillations experiments. In this work, we have studied the imprints of a scalar-mediated NSI in three upcoming long-baseline (LBL) experiments (DUNE, T2HK, T2HKK). The effects of scalar NSI appears as a medium-dependent correction to the neutrino mass term. Its contribution scales linearly with matter density, making LBL experiments a suitable candidate to probe its effects. We show that the scalar NSI may significantly impact the oscillation probabilities, event rates at the detectors and the $χ^2$-sensitivities of $δ_{CP}$ measurements. We present the results of a combined analysis involving the LBL experiments (DUNE+T2HK, DUNE+T2HKK, DUNE+T2HK+T2HKK) which offer a better capability of constraining the scalar NSI parameters as well as an improved sensitivity towards CP-violation.

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arXiv2022

Exploring the effects of Scalar Non Standard Interactions on the CP violation sensitivity at DUNE

The Neutrino oscillations have provided an excellent opportunity to study new-physics beyond the Standard Model, popularly known as BSM. The unknown couplings involving neutrinos, termed non-standard interactions (NSI), may appear as `new-physics' in different neutrino experiments. The neutrino NSI offers significant effects on neutrino oscillations and CP-sensitivity, which may be probed in various neutrino experiments. The idea of neutrinos coupling with a scalar has evolved recently and looks promising. The effects of scalar NSI may appear as a perturbation to the neutrino mass matrix in the neutrino Hamiltonian. It modifies the neutrino mass matrix and may provide a direct possibility of probing neutrino mass models. As the scalar NSI affects the neutrino mass matrix in the Hamiltonian, its effect is energy independent. Moreover, the matter effects due to scalar NSI scales linearly with the matter density. In this work, we have performed a model-independent study of the effects of scalar NSI at long baseline neutrino experiments, taking DUNE as a case study. We have performed such a thorough study for DUNE for the first time. Various neutrino parameters may get affected due to the inclusion of scalar NSI as it modifies the effective mass matrix of neutrinos. We have explored the impact of scalar NSI in neutrino oscillations and its impact on the measurements of various mixing parameters. We have probed the effects of scalar NSI on different oscillation channels relevant to the experiment. We have also explored the impact of various possible elements in the scalar NSI term on the CP-violation sensitivity at DUNE.

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