arXiv subjects

Sushant K. Raut

Publications and source records attributed to Sushant K. Raut.

At least 19 recordsLinked to original sources

arXiv2026

Interplay of CPT-Violating and CPT-Conserving Lorentz Invariance Violation at DUNE

We present a study of Lorentz invariance violation (LIV) in neutrino oscillations, with primary emphasis on the interplay between CPT-violating and CPT-conserving Standard Model Extension (SME) coefficients. We find that $a_{ee}$ and $a_{ττ}$ dominate among the diagonal LIV coefficients, whereas $a_{eμ}$ and $a_{eτ}$ provide the most significant off-diagonal contributions. In contrast, the corresponding $c_{αβ}$ coefficients have comparatively sub-leading effects. Taking DUNE as a representative long-baseline experiment, we show that the sensitivity to CP violation is modified by LIV in a parameter-specific manner. We find correlations between off-diagonal LIV parameters, and non-trivial dependence on the new phases. In absence of LIV, DUNE is expected to establish CP violation at $5σ$ for a limited fraction of $δ_{CP}$ values. We find that the presence of $a_{ee}$, $a_{ττ}$, $a_{eμ}$ and $a_{eτ}$ weakens the CP discovery potential, reducing the achievable significance to below $3σ$ over a substantial fraction of $δ_{\rm CP}$. The independent impact of $c_{αβ}$ terms also results in suppression, but in combination with $a_{αβ}$, they introduce degeneracies, complicating the extraction of $δ_{CP}$. This generally results in a deterioration of CP violation sensitivities below $5σ$. These findings emphasize the importance of incorporating LIV effects in precision oscillation studies at upcoming long-baseline experiments.

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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

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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arXiv2022

Sterile Neutrinos: Propagation in Matter and Sensitivity to Sterile Mass Ordering

We analytically calculate the neutrino conversion probability $P_{μe}$ in the presence of sterile neutrinos, with exact dependence on $Δm^2_{41}$ and with matter effects explicitly included. Using perturbative expansion in small parameters, the terms involving the small mixing angles $θ_{24}$ and $θ_{34}$ can be separated out, with $θ_{34}$ dependence only arising due to matter effects. We express $P_{μe}$ in terms of the quantities of the form $\sin(x)/x$, which helps in elucidating its dependence on matter effects and a wide range of $Δm^2_{41}$ values. Our analytic expressions allow us to predict the effects of the sign of $Δm^2_{41}$ at a long baseline experiment like DUNE. We numerically calculate the sensitivity of DUNE to the sterile mass ordering and find that this sensitivity can be significant in the range $|Δm^2_{41}| \sim (10^{-4} - 10^{-2})$ eV$^2$, for either mass ordering of active neutrinos. The dependence of this sensitivity on the value of $Δm^2_{41}$ for all mass ordering combinations can be explained by investigating the resonance-like terms appearing due to the interplay between the sterile sector and matter effects.

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arXiv2020

Probing muonic charged current nonstandard interactions at decay-at-rest facilities in conjunction with T2HK

The muon decay-at-rest ($μ$-DAR) facility provides us with an ideal platform to probe purely muonic charged-current nonstandard neutrino interactions (NSIs). We propose to probe this class of NSI effects using antineutrinos from a $μ$-DAR source in conjunction with neutrinos from the future Tokai to Kamioka superbeam experiment with megaton Hyper Kamiokande detector (T2HK). Even though muonic NSIs are absent in neutrino production at T2HK, we show that our proposed hybrid setup comprising $μ$-DAR and T2HK helps in alleviating the parameter degeneracies that can arise in data. Analytic considerations reveal that the oscillation probability is most sensitive to the NSI parameter in the $μ$-e sector. For this parameter, we show that the $μ$-DAR setup can improve on the existing bounds down to around 0.01, especially when the data are combined with neutrino data from T2HK experiment due to the lifting of parameter degeneracies. The high precision with which $μ$-DAR can measure $δ_{\rm{CP}}$ is shown to be robust even in the presence of the considered NSIs. Finally, we show that the combination of $μ$-DAR along with T2HK can also be used to put mild constraints on the NSI phase in the vicinity of the maximal CP-violating value for the chosen benchmark value of $\varepsilon^{μe}_{μe}=0.01$.

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arXiv2019

Neutrino oscillations at dual baselines

Beam neutrino oscillation experiments typically employ only one detector at a certain baseline, apart from the near detector that measures the unoscillated neutrino flux at the source. Lately, there have been discussions of having detectors at two different baselines in one of the future long-baseline neutrino oscillation experiments. We study the potential advantage of a general dual-baseline system and perform analysis with a specific example of the envisioned T2HKK experiment. We introduce a new parameter to exploit the correlation between the oscillations at both baselines, and show how it can help in determining the mass hierarchy and the CP phase in the neutrino sector. Our study and findings can be generically used for any dual-baseline system.

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arXiv2017

Synergies and complementarities between proposed future neutrino projects

Measuring the unknown neutrino oscillation parameters is one of the main aims in neutrino physics today. The measurement of these parameters is severely affected by the presence of degeneracies in the parameter space. Various neutrino oscillation projects have been proposed to measure them. In this overview talk, we will discuss some of the proposed neutrino experiments and the synergies between them that can enhance their future physics reach.

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arXiv2017

Matter effects at the T2HK and T2HKK experiments

Determining the neutrino mass hierarchy and measuring the CP-violating phase $δ_{CP}$ are two of the main aims in neutrino physics today. The upcoming T2HK (with small matter effects and high statistics) and DUNE (with large matter effects) experiments have been shown to have excellent sensitivity to $δ_{CP}$ and the neutrino mass hierarchy, respectively. The recent T2HKK proposal aims to improve the hierarchy sensitivity of T2HK by placing one of the two tanks of the HK detector at a site in Korea, to collect data at $\sim 1100$ km baseline. In light of the fact that DUNE will anyway collect data at $\sim 1300$ km, we explore whether it is advantageous to collect additional long-baseline data as proposed with T2HKK, or to enhance the $δ_{CP}$-precision with the `conventional' T2HK by keeping both detector tanks in Japan. We do this by comparing the physics reach of these two options in conjunction with DUNE. We find that DUNE+T2HKK is better at excluding the wrong hierarchy, reaching $Δχ^2 > 175$ irrespective of the true parameters. While DUNE+T2HK can measure $δ_{CP}$ with more precision in some parts of the parameter space, both DUNE+T2HK and DUNE+T2HKK perform equally well near the current best-fit point, giving a $δ_{CP}$ width of around $15^\circ$. The T2HKK setup allows us to correlate and constrain the systematic errors between the two detectors collecting data from the same source, which can increase the sensitivity of the experiment by up to 25\%. Such a reduction of the systematic errors is crucial for determining the oscillation parameters with greater significance.

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arXiv2017

Texture zeros of low-energy Majorana neutrino mass matrix in 3+1 scheme

In this work we revisit the zero textures in low energy Majorana neutrino mass matrix when the active neutrino sector is extended by a light sterile neutrino in the eV scale i.e., the 3+1 scheme. In 3+1 scenario, the low energy neutrino mass matrix ($m_ν$) has ten independent elements. Thus in principle one can have minimum one-zero texture to maximum ten-zero texture. We summarize the previous results of one, two, three and four-zero textures which already exist in the literature and present our new results on five-zero textures. In our analysis we find that among six possible five-zero textures, only one is allowed by the present data. We discuss possible theoretical model which can explain the origin of the allowed five-zero texture and discuss other possible implications of such a scenario. Our results also concludes that in 3+1 scheme, one can not have more than five-zeros in $m_ν$.

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arXiv2017

A hybrid setup for fundamental unknowns in neutrino oscillations using T2HK ($ν$) and $μ$-DAR ($\barν$)

Neutrino mass hierarchy, CP-violation, and octant of $θ_{23}$ are the fundamental unknowns in neutrino oscillations. In order to address all these three unknowns, we study the physics reach of a setup, where we replace the antineutrino run of T2HK with antineutrinos from muon decay at rest ($μ$-DAR). This approach has the advantages of having higher statistics in both neutrino and antineutrino modes, and lower beam-on backgrounds for antineutrino run with reduced systematics. We find that a hybrid setup consisting of T2HK ($ν$) and $μ$-DAR ($\barν$) in conjunction with full exposure from T2K and NO$ν$A can resolve the issue of mass hierarchy at greater than 3$σ$ C.L. irrespective of the choices of hierarchy, $δ_{\mathrm{CP}}$, and $θ_{23}$. This hybrid setup can also establish the CP-violation at 5$σ$ C.L. for $\sim$ 55% choices of $δ_{\mathrm{CP}}$, whereas the same for conventional T2HK ($ν+ \barν$) setup along with T2K and NO$ν$A is around 30%. As far as the octant of $θ_{23}$ is concerned, this hybrid setup can exclude the wrong octant at 5$σ$ C.L. if $θ_{23}$ is at least $3^{\circ}$ away from maximal mixing for any $δ_{\mathrm{CP}}$.

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arXiv2017

Implications of $δ_{CP}=-90^\circ$ towards determining hierarchy and octant at T2K and T2K-II

The T2K experiment has provided the first hint for the best-fit value for the leptonic CP phase $δ_{CP} \sim -90^\circ$ from neutrino data. This is now corroborated by the NO$ν$A neutrino runs. We study the implications for neutrino mass hierarchy and octant of $θ_{23}$ in the context of this data assuming that the true value of $δ_{CP}$ in nature is $-90^\circ$. Based on simple arguments on degeneracies in the probabilities we show that a clear signal of $δ_{CP}=-90^\circ$ coming from T2K neutrino (antineutrino) data is only possible if the true hierarchy is normal and the true octant is higher (lower). Thus if the T2K neutrino and antineutrino data are fitted separately and both give the true value of $δ_{CP}=-90^\circ$, this will imply that nature has chosen the true hierarchy to be normal and $θ_{23} \approx 45^\circ$. However we find that the combined fit of neutrino and antineutrino data will still point to true hierarchy as normal but the octant of $θ_{23}$ will remain undetermined. We do our analysis for both, the current projected exposure ($7.8 \times 10^{21}$ pot) and planned extended exposure ($20 \times 10^{21}$ pot). We also present the CP discovery potential of T2K emphasizing on the role of antineutrinos. We find that one of the main contribution of the antineutrino data is to remove the degenerate solutions with the wrong octant. Thus the antineutrino run plays a more significant role for those hierarchy-octant combinations for which this degeneracy is present. If this degeneracy is absent, then only neutrino run gives a better result for fixed $θ_{13}$. However if we marginalize over $θ_{13}$ then, sensitivity corresponding to mixed run can be better than pure neutrino run.

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arXiv2016

Analysis of four-zero textures in $3+1$ framework

The presence of a zero texture in the neutrino mass matrix can indicate the presence of an underlying symmetry which can generate neutrino mass and mixing. In this paper, for the first time we study the four-zero textures of the low energy neutrino mass matrix in the presence of an extra light-sterile neutrino i.e., the 3+1 neutrino scheme. In our analysis we find that out of the 210 possible four-zero textures only 15 textures are allowed. We divide the allowed four-zero textures into two classes -- class $A$ in which the value of mass matrix element $M_{ee}$ is zero and class $B$ in which $M_{ee}$ is non-zero. In this way we obtain ten possible four-zero textures in class $A$ and five possible four-zero textures in class $B$. In our analysis we find that, for normal hierarchy the allowed number of textures in class $A$ ($B$) is nine (three). For the case of inverted hierarchy we find that, two textures in class $A$ are disallowed and these textures are different from the disallowed textures for normal hierarchy in class $A$. However, we find that all the five textures in class $B$ are allowed for the inverted hierarchy. Based on analytic expressions for the elements $M_{αβ}$, we discuss the reasons for certain textures being disallowed. We also discuss the correlations between the different parameters of the allowed textures. Finally, we present the implications of our study on experimental searches for neutrinoless double beta decay.

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arXiv2016

A combined study of source, detector and matter non-standard neutrino interactions at DUNE

We simultaneously investigate source, detector and matter non-standard neutrino interactions at the proposed DUNE experiment. Our analysis is performed using a Markov Chain Monte Carlo exploring the full parameter space. We find that the sensitivity of DUNE to the standard oscillation parameters is worsened due to the presence of non-standard neutrino interactions. In particular, there are degenerate solutions in the leptonic mixing angle $θ_{23}$ and the Dirac CP-violating phase $δ$. We also compute the expected sensitivities at DUNE to the non-standard interaction parameters. We find that the sensitivities to the matter non-standard interaction parameters are substantially stronger than the current bounds (up to a factor of about 15). Furthermore, we discuss correlations between the source/detector and matter non-standard interaction parameters and find a degenerate solution in $θ_{23}$. Finally, we explore the effect of statistics on our results.

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arXiv2016

Maximising the DUNE early physics output with current experiments

The Deep Underground Neutrino Experiment (DUNE) is a proposed next generation superbeam experiment at Fermilab. Its aims include measuring the unknown neutrino oscillation parameters -- the neutrino mass hierarchy, the octant of the mixing angle $θ_{23}$ and the CP violating phase $δ_{CP}$. The current and upcoming experiments T2K, NOvA and ICAL@INO will also be collecting data for the same measurements. In this paper, we explore the sensitivity reach of DUNE in combination with these other experiments. We evaluate the least exposure required by DUNE to determine the above three unknown parameters with reasonable confidence. We find that for each case, the inclusion of data from T2K, NOvA and ICAL@INO help to achieve the same sensitivity with a reduced exposure from DUNE thereby helping to economize the configuration. Further, we quantify the effect of the proposed near detector on systematic errors and study the consequent improvement in sensitivity. We also examine the role played by the second oscillation cycle in furthering the physics reach of DUNE. Finally, we present an optimization study of the neutrino-antineutrino running of DUNE.

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arXiv2016

New look at the degeneracies in the neutrino oscillation parameters, and their resolution by T2K, NO$ν$A and ICAL

At present the three major unknowns in neutrino oscillation parameters are the mass hierarchy, the octant of $θ_{23}$ and the CP phase $δ_{CP}$. It is well known that the presence of hierarchy$-δ_{CP}$ and octant degeneracies affects the unambiguous determination of these parameters. In this paper we show that a comprehensive way to study the remaining parameter degeneracies is in the form of a generalized hierarchy-$θ_{23}$ - $δ_{CP}$ degeneracy. We show that the wrong-hierarchy and/or wrong-octant solutions can be further classified into eight different solutions depending on whether they occur with the wrong or right value of $δ_{CP}$. These eight solutions are different from the original eightfold degenerate solutions and can exist, in principle, even if $θ_{13}$ is known. These multiple solutions, apart from affecting the determination of the true hierarchy and octant, also affect the accurate estimation of $δ_{CP}$. We identify which of these eight different degenerate solutions can occur in the test ($θ_{23} - δ_{CP}$) parameter space, taking the long-baseline experiment NO$ν$A running in the neutrino mode as an example. The inclusion of the NO$ν$A antineutrino run removes the wrong-octant solutions appearing with both right and wrong hierarchy. Adding T2K data to this resolves the wrong hierarchy -- right octant solutions to a large extent. The remaining wrong hierarchy solutions can be removed by combining NO$ν$A + T2K with atmospheric neutrino data. We demonstrate this using ICAL@INO as the prototype atmospheric neutrino detector. We find that the degeneracies can be resolved at the $2σ$ level by the combined data set, for the true parameter space considered in the study.

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arXiv2015

Exploring Source and Detector Non-Standard Neutrino Interactions at ESS$ν$SB

We investigate source and detector non-standard neutrino interactions at the proposed ESS$ν$SB experiment. We analyze the effect of non-standard physics at the probability level, the event-rate level and by a full computation of the ESS$ν$SB setup. We find that the precision measurement of the leptonic mixing angle $θ_{23}$ at ESS$ν$SB is robust in the presence of non-standard interactions, whereas that of the leptonic CP-violating phase $δ$ is worsened at most by a factor of two. We compute sensitivities to all the relevant source and decector non-standard interaction parameters and find that the sensitivities to the parameters $\varepsilon^s_{μe}$ and $\varepsilon^d_{μe}$ are comparable to the existing limits in a realistic scenario, while they improve by a factor of two in an optimistic scenario. Finally, we show that the absence of a near detector compromises the sensitivity of ESS$ν$SB to non-standard interactions.

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arXiv2015

Can the hint of $δ_{CP}$ from T2K also indicate the hierarchy and octant ?

The T2K neutrino data has already given a hint for the best-fit value of the leptonic CP phase $δ_{CP}$ as $-90^\circ$. In this paper we ask the question that if this hint is confirmed by the subsequent neutrino and anti-neutrino runs of T2K, then can it also give any information about the other two remaining unknown oscillation parameters - the neutrino mass hierarchy and octant of $θ_{23}$. We find that if T2K runs in only neutrino mode with its full targeted exposure, then $δ_{CP} = -90^\circ$ would indicate the true hierarchy as normal and the true octant as higher. On the other hand if T2K runs in equal neutrino and anti-neutrino mode then the true hierarchy can be confirmed as normal but the octant will remain undetermined. We have also studied the effect of anti-neutrino runs on CP sensitivity of T2K.

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arXiv2014

Probing CP violation with the three years ultra-high energy neutrinos from IceCube

The IceCube collaboration has recently announced the discovery of ultra-high energy neutrino events. These neutrinos can be used to probe their production source, as well as leptonic mixing parameters. In this work, we have used the first IceCube data to constrain the leptonic CP violating phase $δ_{cp}$. For this, we have analyzed the data in the form of flux ratios. We find that the fit to $δ_{cp}$ depends on the assumptions made on the production mechanism of these astrophyscial neutrinos. Consequently, we also use this data to impose constraints on the sources of the neutrinos.

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