arXiv subjects

Srubabati Goswami

Publications and source records attributed to Srubabati Goswami.

At least 19 recordsLinked to original sources

arXiv2026

Testing predictions of discrete flavour and modular symmetries at DUNE and Hyper-K with JUNO constraints

We study fixed-column predictions of the lepton mixing matrix that arise from residual symmetries originating in a class of discrete flavour and modular symmetries. While the recent high-precision determination of $\sin^{2}θ_{12}$ by JUNO already constrains part of these predictions, the remaining viable scenarios are primarily characterized by non-trivial correlations between $\sin^{2}θ_{23}$ and the Dirac CP phase $δ_{\rm CP}$, which are currently only weakly constrained. This motivates a detailed investigation of the sensitivities of next-generation long-baseline neutrino experiments to these scenarios. For the phenomenologically viable fixed-column predictions that can constitute a column of the lepton mixing matrix, we derive precise $\sin^{2}θ_{23}$--$δ_{\rm CP}$ correlations and use them to generate test-event samples, marginalising over the remaining oscillation parameters. We perform detailed simulations for DUNE and Hyper-K, presenting the allowed regions in the $\sin^{2}θ_{23}$--$δ_{\rm CP}$ plane. We also evaluate, as a function of experimental exposure (determined by the run time), the fraction of $δ_{\rm CP}$ values for which these theoretical predictions can be ruled out at more than $3σ$ CL. Our results show that the combined sensitivity of DUNE and Hyper-K provides a robust test of fixed-column lepton-mixing predictions.

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arXiv2026

Thermal Leptogenesis in the BNT Model of Neutrino Mass

We investigate neutrino mass and thermal leptogenesis in the Babu-Nandi-Tavartkiladze (BNT) model featuring a scalar quadruplet ($Φ$) and a pair of vector-like fermion triplets ($Σ$). In this framework, neutrino masses are generated via an effective dimension-7 operator $LLHH(H^{\dagger}H)/Λ^3$ at the tree level and via the dimension-5 operator $LLHH/Λ$ at the one-loop level. It naturally accommodates sub-eV neutrino masses even if the new physics scale $Λ$ is $\mathcal{O}(\rm TeV)$, thus making the model a compelling target for experimental searches. We explore the viability of thermal leptogenesis in this model, which is distinct from the canonical seesaw-based leptogenesis due to the presence of vector-like fermions. We find that leptogenesis is viable for $M_Σ\gtrsim 10^{7}$ GeV for a hierarchical spectrum of fermion triplets. However, in the quasi-degenerate regime, resonant enhancement of the $CP$ asymmetry lowers this scale down to $\mathcal{O}({\rm TeV})$, reconciling successful leptogenesis with the originally motivated TeV-scale phenomenology and testability of the model at colliders.

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arXiv2026

Enhancing the sensitivity to neutrino oscillation parameters using synergy between T2K, NO$ν$A and JUNO

We study the impact of combining the present NO$ν$A and T2K data with simulated data from the JUNO experiment on the determination of the leptonic CP phase and the neutrino mass hierarchy. The current NO$ν$A data exhibit a hierarchy--$δ_{\rm CP}$ degeneracy, admitting both normal hierarchy (NH) with $δ_{\rm CP} \in [0,180^\circ]$, and inverted hierarchy (IH) with $δ_{\rm CP} \in [180^\circ,360^\circ]$ solutions at comparable significance, while T2K prefers $δ_{\rm CP}\simeq 270^\circ$ for both hierarchies, leading to a $2σ$ tension between the two experiments for normal hierarchy. Using detailed GLoBES simulations, we show that future JUNO data with excellent hierarchy sensitivity, can lift the hierarchy--$δ_{\rm CP}$ degeneracy in NO$ν$A and strengthen the hierarchy reach of T2K in spite of having no $δ_{\rm CP}$ sensitivity. Allowing the hierarchy to be a free parameter in the fit, if the true ordering is IH, JUNO aligns the NO$ν$A and T2K allowed regions and resolves their present tension; if NH is true, the tension continues to persist. We also show that JUNO's precise measurement of $|Δ_{31}|$ leads to improved constraints on $\sin^2θ_{23}$ and $δ_{\rm CP}$ for normal mass hierarchy in NO$ν$A even though JUNO itself is insensitive to these parameters. Finally, updated solar parameter measurements from JUNO's first data release further enhance the combined precision. Our results demonstrate that JUNO plays a crucial synergistic role in the global neutrino oscillation programme, enabling a more robust determination of the mass ordering and improving the sensitivity to the CP phase when combined with long-baseline data.

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arXiv2026

Neutrino mass variables in 3 active and 2 sterile neutrino scenario

The three-flavor framework of neutrino oscillations successfully explains most experimental results, but persistent anomalies at short- and long-baseline experiments hint at the existence of additional light sterile states. In particular, eV-scale sterile neutrinos are motivated by LSND and MiniBooNE results, while sub-eV sterile states with mass-squared differences at the $10^{-2}$ and $10^{-5}$~eV$^2$ scales have been proposed to address the T2K--NO$ν$A tension and the absence of the expected upturn in the solar neutrino energy spectrum, respectively. Such sterile states are singlets under the Standard Model gauge group and mix only through their admixture with active neutrinos. In this work, we investigate the phenomenology of the $3+2$ scenario, incorporating one eV-scale sterile neutrino together with a sub-eV state, and analyze their impact on absolute-mass related observables: the sum of neutrino masses $Σ$ constrained by cosmology, the effective electron neutrino mass $m_β$ from beta decay, and the effective Majorana mass $m_{ββ}$ probed in neutrinoless double beta decay. We demonstrate that the presence of two sterile states can significantly modify the allowed parameter space compared to the three-flavor and $3+1$ frameworks, with some mass-ordering schemes already disfavored by current cosmological and laboratory limits. Finally, we assess the implications of upcoming sensitivities from KATRIN, Project~8, and LEGEND-1000, highlighting the complementary role of sub-eV sterile neutrinos in probing physics beyond the minimal three-flavor paradigm.

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arXiv2026

Universal Seesaw Leptogenesis

We study the implications for leptogenesis in a class of left-right symmetric model, where all fermion masses are induced through the Universal Seesaw mechanism. Unlike conventional analyses, we do not use the decays of the neutrino embedded in the right-chiral lepton doublet, but rather those of the gauge-singlet mediators required for neutrino mass generation in the canonical Type-I seesaw. This model features a generalized parity symmetry, which is motivated by the solution to the strong $CP$ problem. Since this discrete symmetry doubles the fermionic degrees of freedom in this model, we can generate the required $CP$ violation in the heavy fermion decays with only a single generation of mediators. One of the distinct features of our scenario is that the bounds from thermalization or washout via gauge interactions typically encountered in the canonical left-right symmetric models do not apply here. Moreover, the heavy mediators can decay to both the left and the right-chiral neutrinos, leading to a cancellation in the resulting baryon asymmetry for decays above the left-right symmetry breaking scale. We discuss ways to avoid this cancellation and show that low scale left-right symmetry breaking above the current collider limits $v_R > 18$ TeV is viable. The right chiral neutrinos also obtain their masses from the seesaw mechanism, and the lightest one turns out to have a sub-eV scale mass. We find that its abundance is consistent with standard cosmology, and it acts as potentially observable dark radiation.

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arXiv2026

Probing Geometrical NSI at the DUNE experiment

In this work, we investigate the implications of a novel non-standard interaction (NSI) of neutrinos. This interaction is geometric in origin -- it arises because the propagation of fermions in curved spacetime induces torsion. This torsion is non-propagating and can be eliminated from the action, resulting in a four-fermion interaction in a torsion-free background. The new interaction modifies the behaviour of the neutrinos passing through matter by introducing additional coupling terms, resulting in a new component in the effective potential. As a result, the neutrino oscillation probabilities in matter are altered. The relevant probabilities are computed using the Cayley-Hamilton formalism. We then numerically explore the potential to probe these torsion-induced NSI in the DUNE experiment. We obtain the bounds on the parameters characterizing the torsional effects. By selecting representative values of torsion parameters to which the DUNE experiment is sensitive, we analyse how these geometric interactions affect the experiment's sensitivity to determine neutrino mass hierarchy, the octant of the 2-3 leptonic mixing angle, and the CP phase. We also examine the new parameter degeneracies introduced by torsion effects and assess their impact on the overall sensitivities of DUNE. We find that the additional parameter degeneracies in the presence of torsion significantly affect the octant sensitivity.

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arXiv2026

Scalar-induced Neutrinoless Double Beta Decay in $SU(5)$

We discuss the role of heavy scalar fields in mediating neutrinoless double beta decay $(0νββ)$ within the $SU(5)$ Grand Unified Theory framework, extended suitably to include neutrino mass. In such a minimal realistic $SU(5)$ setup for fermion masses, the scalar contributions to $0νββ$ are extremely suppressed as a consequence of the proton decay bound. We circumvent this problem by imposing a discrete ${\cal Z}_3$ symmetry. However, the scalar contributions to $0νββ$ remain suppressed in this $SU(5) \times {\cal Z}_3$ model due to the neutrino mass constraint. We find that the $0νββ$ contribution can be enhanced by extending the scalar sector with an additional $\mathbf{15}$-dimensional scalar representation with suitable ${\cal Z}_3$ charge. Such an extension not only yields realistic fermion mass spectra but also leads to experimentally testable predictions in upcoming ton-scale $0νββ$ searches, which can be used as a sensitive probe of the new scalars across a broad range, from LHC-accessible scales up to $\sim 10^{10}\,\text{GeV}$.

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arXiv2025

Opening up New Parameter Space for Sterile Neutrino Dark Matter

Sterile neutrinos are compelling dark matter (DM) candidates, yet the minimal production mechanism solely based on active ($ν_a$)-sterile ($ν_s$) oscillations is excluded by astrophysical observations. Non-standard self-interactions in either active ($ν_a-ν_a$) or sterile ($ν_s-ν_s$) sector are known to alter the sterile neutrino DM production in the early Universe, which could alleviate the tension with astrophysical constraints to some extent. Here we propose a novel solution where scalar-mediated non-standard interactions between active and sterile neutrinos ($ν_a-ν_s$) generate new production channels for $ν_s$, independent of the active-sterile mixing and without the need for any fine-tuned resonance or primordial lepton asymmetry. This framework enables efficient sterile neutrino DM production even at vanishingly small mixing angles and opens up new viable regions of parameter space that can be tested with future $X$-ray and gamma-ray observations.

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arXiv2025

Neutrino Theory in the Precision Era

This document summarises discussions on future directions in theoretical neutrino physics, which are the outcome of a neutrino theory workshop held at CERN in February 2025. The starting point is the realisation that neutrino physics offers unique opportunities to address some of the most fundamental questions in physics. This motivates a vigorous experimental programme which the theory community fully supports. \textbf{A strong effort in theoretical neutrino physics is paramount to optimally take advantage of upcoming neutrino experiments and to explore the synergies with other areas of particle, astroparticle, and nuclear physics, as well as cosmology.} Progress on the theory side has the potential to significantly boost the physics reach of experiments, as well as go well beyond their original scope. Strong collaboration between theory and experiment is essential in the precision era. To foster such collaboration, \textbf{we propose to establish a CERN Neutrino Physics Centre.} Taking inspiration from the highly successful LHC Physics Center at Fermilab, the CERN Neutrino Physics Centre would be the European hub of the neutrino community, covering experimental and theoretical activities.

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arXiv2024

Neutrinoless Double Beta Decay from Scalar Leptoquarks: Interplay with Neutrino Mass and Flavor Physics

We perform a comprehensive analysis of neutrinoless double beta decay and its interplay with low-energy flavor observables in a radiative neutrino mass model with scalar leptoquarks $S_1(\bar{3},1,1/3)$ and $\widetilde{R}_2(3,2,1/6)$. We carve out the parameter region consistent with constraints from neutrino mass and mixing, collider searches, as well as measurements of several flavor observables, such as muon and electron anomalous magnetic moments, charged lepton flavor violation and rare (semi)leptonic kaon and $B$-meson decays, including the recent anomalies in $R_{D^{(*)}}$ and $B\to Kν\barν$ observables. We perform a global analysis to all existing constraints and show the (anti)correlations between all relevant Yukawa couplings satisfying these restrictions. We find that the most stringent constraint on the parameter space comes from $μ\to e$ conversion in nuclei and $K^{+} \rightarrow\, π^{+}ν\barν$ decay. We also point out a tension between the muon and electron $(g-2)$ anomalies in this context. Taking benchmark values from the combined allowed regions, we study the implications for neutrinoless double beta decay including both the canonical light neutrino and the leptoquark contributions. We find that for normal ordering of neutrino masses, the leptoquark contribution removes the cancellation region that occurs for the canonical case. The effective mass in presence of leptoquarks can lie in the desert region between the standard normal and inverted ordering cases, and this can be probed in future ton-scale experiments like LEGEND-1000 and nEXO.

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arXiv2024

Effect of invisible neutrino decay on neutrino oscillation at long baselines

In this article, we study the effect of invisible neutrino decay of the third neutrino state for accelerator neutrino experiments at two different baselines, 1300 km with a liquid argon time projection chamber (LArTPC) detector (similar to DUNE) and 2588 km with a water Cherenkov detector (similar to P2O). For such baselines, the matter effect starts to become important. Our aim is to ascertain the sensitivity to mass hierarchy and octant of $θ_{23}$ in these two experiments in the presence of a decaying neutrino state. We compare and contrast the results of the two experimental setups. We find that, in general, hierarchy sensitivity decreases in the presence of decay. However, if we consider decay only in the opposite hierarchy (test scenario), in the 2588 km setup, the hierarchy sensitivity with the true hierarchy as IH is larger than the no decay case. We also study the dependence of hierarchy sensitivity with true $θ_{23}$. We find that the dominant muon background in P2O plays an important role in how the hierarchy sensitivity depends on $θ_{23}$. The octant sensitivity for both setups increases in the presence of decay except for the LArTPC setup in case true $θ_{23}=49^\circ$. To understand the octant sensitivity results in the two setups, we check the synergy in sensitivity between electron and muon channels as a function of test $θ_{23}$. We also study the degeneracies in the test $θ_{23}-δ_{CP}$ plane and find that combined analysis of the two setups removes all the degeneracies in the test $θ_{23}-δ_{CP}$ plane at $5σ$ significance.

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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

Constraining the mass-spectra in the presence of a light sterile neutrino from absolute mass-related observables

The framework of three-flavor neutrino oscillation is a well-established phenomenon, but results from the short-baseline experiments, such as the Liquid Scintillator Neutrino Detector (LSND) and MiniBooster Neutrino Experiment (MiniBooNE), hint at the potential existence of an additional light neutrino state characterized by a mass-squared difference of approximately $1\,\rm eV^2$. The new neutrino state is devoid of all Standard Model (SM) interactions, commonly referred to as a 'sterile' state. In addition, a sterile neutrino with a mass-squared difference of $10^{-2}$ $\rm eV^2$ has been proposed to improve the tension between the results obtained from the Tokai to Kamioka (T2K) and the NuMI Off-axis $ν_e$ Appearance (NO$ν$A) experiments. Further, the non-observation of the predicted upturn in the solar neutrino spectra below 8 MeV can be explained by postulating an extra light sterile neutrino state with a mass-squared difference around $10^{-5} \rm eV^2$. The hypothesis of an additional light sterile neutrino state introduces four distinct mass spectra depending on the sign of the mass-squared difference. In this paper, we discuss the implications of the above scenarios on the observables that depend on the absolute mass of the neutrinos, namely the sum of the light neutrino masses $(Σ)$ from cosmology, the effective mass of the electron neutrino from beta decay $(m_β)$, and the effective Majorana mass $( m_{ββ})$ from neutrinoless double beta decay. We show that some scenarios can be disfavored by the current constraints of the above variables. The implications for projected sensitivity of Karlsruhe Tritium Neutrino Experiment (KATRIN) and future experiments like Project-8, next Enriched Xenon Observatory (nEXO) have been discussed.

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arXiv2023

Matter effect in presence of a sterile neutrino and resolution of the octant degeneracy using a liquid argon detector

Results from the experiments like LSND, and MiniBooNE hint towards the possible presence of an extra eV scale sterile neutrino. The addition of such a neutrino will significantly impact the standard three flavour neutrino oscillations; in particular, it can give rise to additional degeneracies due to new sterile parameters. In our work, we investigate how the sensitivity to determine the octant of the neutrino mixing angle $θ_{23}$ is affected by introducing a sterile neutrino to the standard neutrino oscillation framework. We compute the oscillation probabilities in presence of a sterile neutrino, analytically, using the approximation that $Δ_{21}$, the smallest mass squared difference, is zero. We use these probabilities to understand the degeneracies analytically at different baselines. We present our results of the sensitivity to octant of $θ_{23}$ for beam neutrinos using a liquid argon time projection chamber (LArTPC). We also obtain octant sensitivity using atmospheric neutrinos using the same LArTPC detector without any charge identification capability. In addition, we include the charge tagging capability of muon capture in argon which allows one to differentiate between muon neutrino and antineutrino events. The combined sensitivity of beam and atmospheric neutrinos in a similar experimental setup is also delineated. We observe that by combining simulated data from the beam and atmospheric neutrinos (including charge-id for muons), the sensitivity to the octant of $θ_{23}$ for true values of $θ_{23}=41^\circ(49^\circ)$ exceeds $4σ(3σ)$ for more than $50\%$ values of true $δ_{13}$.

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arXiv2023

Sensitivity to CP Discovery in the Presence of Lorentz Invariance Violating Potential at T2HK/T2HKK

Investigation of conservation/violation of CP symmetry in the leptonic sector is very essential in understanding the evolution of the universe. Lorentz invariance and CPT are fundamental symmetries of nature. The violation of Lorentz invariance can also lead to CPT violations. The standard three flavour neutrino oscillation framework presents a scenario to observe the signature of Lorentz invariance and CP violations. This work focuses on the effect of Lorentz invariance violating (LIV) parameters on the sensitivity to CP violation. We investigate the sensitivity in two proposed configurations of the upcoming T2HK experiment: (i) one detector each placed at 295 km and 1100 km, and (ii) two identical detectors at 295 km. This study probes the effect of CPT violating parameters $a_{eμ},a_{eτ},a_{μτ}$.

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arXiv2023

Implications of the DLMA solution of $θ_{12}$ for IceCube data using different astrophysical sources

In this paper, we study the implications of the Dark Large Mixing Angle (DLMA) solutions of $θ_{12}$ in the context of the IceCube data. We study the consequences in the measurement of the neutrino oscillation parameters namely $θ_{23}$ and $δ_{\rm CP}$ in light of both Large Mixing Angle (LMA) and DLMA solutions of $θ_{12}$. We find that it will be impossible for IceCube to determine the $δ_{\rm CP}$ and the true nature of $θ_{12}$ i.e., LMA or DLMA at the same time. This is because of the existence of an intrinsic degeneracy at the Hamiltonian level between these parameters. Apart from that, we also identify a new degeneracy between $θ_{23}$ and two solutions of $θ_{12}$ for a fixed value of $δ_{\rm CP}$. We perform a chi-square fit using three different astrophysical sources, i.e., $μ$ source, $π$ source, and $n$ source to find that both $μ$ source and $π$ source are allowed within $1 σ$ whereas the $n$ source is excluded at $2 σ$. It is difficult to make any conclusion regarding the measurement of $θ_{23}$, $δ_{\rm CP}$ for $μ$ source. However, The $π$ ($n$) source prefers higher (lower) octant of $θ_{23}$ for both LMA and DLMA solution of $θ_{12}$. The best-fit value of $δ_{\rm CP}$ is around $180^\circ$ ($0^\circ/360^\circ$) for LMA (DLMA) solution of $θ_{12}$ whereas for DLMA (LMA) solution of $θ_{12}$, the best-fit value is around $0^\circ/360^\circ$ ($180^\circ$) for $π$ ($n$) source. If we assume the current best-fit values of $θ_{23}$ and $δ_{\rm CP}$ to be true, then the $μ$ and $π$ source prefer the LMA solution of $θ_{12}$ whereas the $n$ source prefers the DLMA solution of $θ_{12}$.

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arXiv2023

Probing mass orderings in presence of a very light sterile neutrino in a liquid argon detector

Results from experiments like LSND and MiniBooNE hint towards the possible presence of an extra eV scale sterile neutrino. The addition of such a neutrino will significantly impact the standard three flavour neutrino oscillations. In particular, it can give rise to additional degeneracies due to additional sterile parameters. For an eV scale sterile neutrino, the cosmological constraints dictate that the sterile state is heavier than the three active states. However, for lower masses of sterile neutrinos, it can be lighter than one and/or more of the three states. In such cases, the mass ordering of the sterile neutrinos also becomes unknown along with the mass ordering of the active states. In this paper, we explore the mass ordering sensitivity in the presence of a sterile neutrino assuming the mass squared difference $|Δ_{41}|$ to be in the range $10^{-4} - 1$ eV$^2$. We study (i) how the ordering of the active states, i.e. the determination of the sign of $Δ_{31}$ gets affected by the presence of a sterile neutrino in the above mass range, (ii) the possible determination of the sign of $Δ_{41}$ for $Δ_{41}$ in the range $10^{-4} - 0.1$ eV$^2$. This analysis is done in the context of a liquid argon detector using both beam neutrinos traveling a distance of 1300 km and atmospheric neutrinos which propagates through a distance ranging from 10 - 10000 km allowing resonant matter effects. Apart from presenting separate results from these sources, we also do a combined study and probe the synergy between these two in giving an enhanced sensitivity.

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arXiv2023

Lowering the scale of fermion triplet leptogenesis with two Higgs doublets

In this paper, we consider the possibility of generating the observed baryon asymmetry of the Universe via leptogenesis in the context of triplet fermion mediated type-III seesaw model of neutrino mass. With a hierarchical spectrum of the additional fermions, the lower bound on the lightest triplet mass is $\sim 10^{10} {\rm~GeV}$ for successful leptogenesis, a couple of orders higher than that of the type-I case. We investigate the possibility of lowering this bound in the framework of two-Higgs-doublet models. We find that the bounds can be lowered down to $10^7$ GeV for a hierarchical spectrum. If we include the flavor effects, then a further lowering by one order of magnitude is possible. We also discuss if such lowering can be compatible with the naturalness bounds on the triplet mass.

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