arXiv subjects

Sabya Sachi Chatterjee

Publications and source records attributed to Sabya Sachi Chatterjee.

At least 19 recordsLinked to original sources

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 $δ_{\rm CP}$.

hep-ph↗

arXiv2026

Oscillating Neutrinos vs. Oscillating Scalars: Constraining Scalar Dark Matter-Induced Neutrino Mass

We consider the hypothesis that neutrino masses are generated by a coupling to an ultra-light (pseudo-)scalar field, which provides the dark matter in the universe. This leads to time-varying neutrino masses with a frequency set by the dark matter mass, with implications for neutrino oscillation data. We use that dark matter is in a virialised state in the galaxy and provide a detailed discussion of the relevant time scales. Using data from the T2K, RENO and JUNO experiments, we show that for dark matter masses smaller than about $3\times 10^{-8}$eV down to the smallest allowed dark matter mass of about $10^{-21}$eV only a fraction of between 9\% to 54\% of the total neutrino mass can arise from the coupling to the background scalar, depending on the value of the scalar mass. Future data from JUNO may improve these limits down to 1\% in certain regions of scalar masses. We focus on a real scalar field, but most of our results hold also for a complex scalar.

hep-ph↗

arXiv2026

Effective Matter Flavor Conversion Mediated by Pseudo-Sterile States as the Possible Origin of Neutrino Oscillation Anomalies

Neutrino oscillation experiments present anomalous results across a vast range of baselines and energies. Here we show that a 3+1 scenario in which sterile neutrinos feel a novel matter potential $V_s$ proportional to background density of ordinary or (asymmetric) dark matter is able to explain several anomalies. At low-energies ($E\lesssim$ 1 TeV) the model behaves as an effective 3-flavor NSI-like scheme among active flavors and eliminates the tension between the two LBL experiments NOvA and T2K provided that the potential is negative and the two sterile mixing angles $θ_{14}$ and $θ_{24}$ are non-zero. A further indication in favor of a negative non-zero potential comes from the anomalous excess of $ν_e$-like events observed in Super-Kamiokande atmospheric neutrinos, which, in the new scenario is explained by a modification of the 3-flavor resonance at few GeV. A high energies ($E\gtrsim $ 1 TeV) the new framework reveals its 4-flavor nature and produces a resonant behavior at $E \simeq$ 10 TeV as hinted at by IceCube. We identify an irreducible 3-level dynamics generating a new resonance in the $(ν_e, ν_μ)$ sector intertwined with two conventional resonances in the $(ν_e, ν_s$) and $(ν_μ, ν_s)$ systems. The novel amplification mechanism manifests with the emergence of effective mixing angles in matter ($θ_{12}^m$ or $θ_{13}^m$) involving active neutrinos. The scenario requires values of $f = V_s/|V_{NC}| \sim -20 $, $Δm^2_{41} \sim 60 $ eV$^2$, $|U_{e4}|^2\simeq \sin^2θ_{14} \simeq 0.01-0.03$ and $|U_{\mu4}|^2 \simeq \sin^2θ_{24}\simeq 10^{-4}-10^{-3}$. Such a very small size of $|U_{\mu4}|^2$ eliminates the tension between IceCube and the other $ν_μ$ disappearance searches. The model can be directly probed by KATRIN, which is very sensitive to the electron-sterile neutrino admixture in the region of high $Δm^2_{41}$.

hep-ph↗

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.

hep-ph↗

arXiv2025

Testing the heavy decaying sterile neutrino hypothesis at the DUNE near detector

One of the most convincing explanations of the LSND and MiniBooNE anomalies relies on a heavy, mostly sterile neutrino with a small muon neutrino component, which decays to an electron neutrino and an invisible light scalar field. We investigate the possibility to test this hypothesis at the near detector complex of the upcoming DUNE experiment. We find that the DUNE liquid argon near detector (ND-LAr) can probe a larger region of the parameter space than the Fermilab SBN program, and may help to confirm or reject a possible hint of $ν_e$ appearance in future MicroBooNE, SBND or ICARUS data. We also argue that it may be possible to distinguish between Dirac and Majorana neutrinos if this scenario is realized in Nature.

hep-ph↗

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.

hep-ph↗

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.

hep-ph↗

arXiv2024

Status of tension between NO$ν$A and T2K after Neutrino 2024 and possible role of non-standard neutrino interactions

In a previous work we have shown that the data presented by the two long-baseline accelerator experiments NO$ν$A and T2K at the Neutrino 2020 conference displayed a tension, and that it could be alleviated by non-standard neutrino interactions (NSI) of the flavor changing type involving the $e-μ$ or the $e-τ$ sectors with couplings $|\varepsilon_{eμ}| \sim |\varepsilon_{eτ}|\sim 0.1$. As a consequence a hint in favor of NSI emerged. In the present paper we reassess the issue in light of the new data released by the two experiments at the Neutrino 2024 conference. We find that the tension in the determination of the standard CP-phase $δ_{\mathrm {CP}}$ extracted by the two experiments in the normal neutrino mass ordering persists and has a statistical significance of $\sim2σ$. Concerning the NSI, we find that including their effects in the fit, the two values of $δ_{\mathrm {CP}}$ preferred by NO$ν$A and T2K return in very good agreement. The current statistical significance of the hint of non zero NSI is $\sim1.8σ$. Further experimental data are needed in order to settle the issue.

hep-ph↗

arXiv2024

Exploring the Sensitivity to Non-Standard Neutrino Interactions of NaI and Cryogenic CsI Detectors at the Spallation Neutron Source

After the first observation of coherent elastic neutrino-nucleus scattering (CE$ν$NS) by the COHERENT collaboration, many efforts are being made to improve the measurement of this process, making it possible to constrain new physics in the neutrino sector. In this paper, we study the sensitivity to non-standard interactions (NSIs) and generalized neutrino interactions (GNIs) of two experimental setups at the Spallation Neutron Source at Oak Ridge National Laboratory: a NaI detector with characteristics similar to the one that is currently being deployed there, and a cryogenic CsI detector proposed at the same facility. We show that a combined analysis of the data from these detectors, whose target nuclei have significantly different proton-to-neutron ratios, could help to partially break the parameter degeneracies arising from the interference between the Standard Model and NSI contributions to the CE$ν$NS cross section, as well as between different NSI parameters. By contrast, only a slight improvement over the current CsI constraints is expected for parameters that do not interfere with the SM contribution.

hep-ph↗

arXiv2023

Constraining Non-Standard Interactions with Coherent Elastic Neutrino-Nucleus Scattering at the European Spallation Source

The European Spallation Source (ESS), currently under construction in Sweden, will provide an intense pulsed neutrino flux allowing for high-statistics measurements of coherent elastic neutrino-nucleus scattering (CEνNS) with advanced nuclear recoil detectors. In this paper, we investigate in detail the possibility of constraining non-standard neutrino interactions (NSIs) through such precision CEνNS measurements at the ESS, considering the different proposed detection technologies, either alone or in combination. We first study the sensitivity to neutral-current NSI parameters that each detector can reach in 3 years of data taking. We then show that operating two detectors simultaneously can significantly improve the expected sensitivity on flavor-diagonal NSI parameters. Combining the results of two detectors turns out to be even more useful when two NSI parameters are assumed to be nonvanishing at a time. In this case, suitably chosen detector combinations can reduce the degeneracies between some pairs of NSI parameters to a small region of the parameter space.

hep-ph↗

arXiv2022

Nonunitarity of the lepton mixing matrix at the European Spallation Source

If neutrinos get mass through the exchange of lepton mediators, as in seesaw schemes, the neutrino appearance probabilities in oscillation experiments are modified due to effective nonunitarity of the lepton mixing matrix. This also leads to new CP phases and an ambiguity in underpinning the ''conventional'' phase of the three-neutrino paradigm. We study the CP sensitivities of various setups based at the European spallation source neutrino super-beam (ESSnuSB) experiment in the presence of nonunitarity. We also examine its potential in constraining the associated new physics parameters. Moreover, we show how the combination of DUNE and ESSnuSB can help further improve the sensitivities on the nonunitarity parameters.

hep-ph↗

arXiv2022

Resolving the NO$ν$A and T2K tension in the presence of Neutrino Non-Standard interactions

The current data of the two long-baseline accelerator experiments NO$ν$A and T2K, shows a tension at more than 90$\%$ C.L. for 2 degrees of freedom, in the determination of the standard CP-phase $δ_{\mathrm {CP}}$ in case of neutrino normal ordering (NO). NO$ν$A measures the value close to $δ_{\mathrm {CP}} \sim 0.8 π$, while T2K prefers the value of $δ_{\mathrm {CP}} \sim 1.4 π$. We show that such a tension can be resolved if one hypothesizes the existence of neutral-current non-standard interactions (NSI) of neutrinos involving the flavor changing type $e-μ$ or the $e-τ$ sectors with couplings $|\varepsilon_{eμ}| \sim |\varepsilon_{eτ}|\sim 0.2$. Remarkably, our analyses show that in the presence of such NSI, both the experiments point towards the same common value of the standard CP-phase $δ_{\mathrm {CP}} \sim 3π/2$, thereby indicating towards the maximal CP-violation in the standard $3ν$ framework. We also show that the best fit values of the new CP-phases $ϕ_{eμ}$ or $ ϕ_{eτ}$ are close to $\sim 3π/2$, hence pointing towards the maximal CP-violation in the NSI sector.

hep-ph↗

arXiv2021

Impact of Improved Energy Resolution on DUNE sensitivity to Neutrino Non-Standard Interactions

The full physics potential of the next-generation Deep Underground Neutrino Experiment (DUNE) is still being explored. In particular, there have been some recent studies on the possibility of improving DUNE's neutrino energy reconstruction. The main motivation is that a better determination of the neutrino energy in an event-by-event basis will translate into an improved measurement of the Dirac $CP$ phase and other neutrino oscillation parameters. To further motivate studies and improvements on the neutrino energy reconstruction, we evaluate the impact of energy resolution at DUNE on an illustrative new physics scenario, viz. non-standard interactions (NSI) of neutrinos with matter. We show that a better energy resolution in comparison to the ones given in the DUNE conceptual and technical design reports may significantly enhance the experimental sensitivity to NSI, particularly when degeneracies are present. While a better reconstruction of the first oscillation peak helps disentangling standard $CP$ effects from those coming from NSIs, we find that the second oscillation peak also plays a nontrivial role in improving DUNE's sensitivity.

hep-ph↗

arXiv2021

Interpretation of NO$ν$A and T2K data in the presence of a light sterile neutrino

We study in detail the impact of a light sterile neutrino in the interpretation of the latest data of the long baseline experiments NO$ν$A and T2K, assessing the robustness/fragility of the estimates of the standard 3-flavor parameters with respect to the perturbations induced in the 3+1 scheme. We find that all the basic features of the 3-flavor analysis, including the weak indication ($\sim$1.4$σ$) in favor of the inverted neutrino mass ordering, the preference for values of the CP-phase $δ_{13} \sim 1.2π$, and the substantial degeneracy of the two octants of $θ_{23}$, all remain basically unaltered in the 4-flavor scheme. Our analysis also demonstrates that it is possible to attain some constraints on the new CP-phase $δ_{14}$. Finally, we point out that, differently from non-standard neutrino interactions, light sterile neutrinos are not capable to alleviate the tension recently emerged between NO$ν$A and T2K in the appearance channel.

hep-ph↗

arXiv2021

Non-standard neutrino interactions as a solution to the NO$ν$A and T2K discrepancy

The latest data of the two long-baseline accelerator experiments NO$ν$A and T2K, interpreted in the standard 3-flavor scenario, display a discrepancy. A mismatch in the determination of the standard CP-phase $δ_{\mathrm {CP}}$ extracted by the two experiments is evident in the normal neutrino mass ordering. While NO$ν$A prefers values close to $δ_{\mathrm {CP}} \sim 0.8 π$, T2K identifies values of $δ_{\mathrm {CP}} \sim 1.4 π$. Such two estimates are in disagreement at more than 90$\%$ C.L. for 2 degrees of freedom. We show that such a tension can be resolved if one hypothesizes the existence of complex neutral-current non-standard interactions (NSI) of the flavor changing type involving the $e-μ$ or the $e-τ$ sectors with couplings $|\varepsilon_{eμ}| \sim |\varepsilon_{eτ}|\sim 0.2$. Remarkably, in the presence of such NSI, both experiments point towards the same common value of the standard CP-phase $δ_{\mathrm {CP}} \sim 3π/2$. Our analysis also highlights an intriguing preference for maximal CP-violation in the non-standard sector with the NSI CP-phases having best fit close to $ϕ_{eμ} \sim ϕ_{eτ}\sim 3π/2$, hence pointing towards imaginary NSI couplings.

hep-ph↗

arXiv2020

Neutrino mass ordering obfuscated by the NSI

Determination of the neutrino mass ordering (NMO) is one of the biggest priorities in the intensity frontier of high energy particle physics. To accomplish that goal a lot of efforts are being put together with the atmospheric, solar, reactor, and accelerator neutrinos. In the standard 3-flavor framework, NMO is defined to be normal if $m_1<m_2<m_3$, and inverted if $m_3<m_1<m_2$, where $m_1$, $m_2$, and $m_3$ are the masses of the three neutrino mass eigenstates $ν_1$, $ν_2$, and $ν_3$ respectively. Interestingly, two long-baseline experiments T2K and NO$ν$A are playing a leading role in this direction and provide a $\sim2.4σ$ indication in favor of normal ordering (NO) which we find in this work. In addition, we examine how the situation looks like in presence of non-standard interactions (NSI) of neutrinos with a special focus on the non-diagonal flavor changing type $\varepsilon_{eτ}$ and $\varepsilon_{eμ}$. We find that the present indication of NO in the standard 3-flavor framework gets completely vanished in the presence of NSI of the flavor changing type involving the $e-τ$ flavors.

hep-ph↗

arXiv2020

Neutrino mass ordering obscured by non-standard interactions

One of the major open questions in particle physics is the issue of the neutrino mass ordering (NMO). The current data of the two long-baseline experiments NO$ν$A and T2K, interpreted in the standard 3-flavor scenario, provide a $\sim2.4σ$ indication in favor of the normal neutrino mass ordering. We show that such an indication is completely washed out if one assumes the existence of neutral-current non-standard interactions (NSI) of the flavor changing type involving the $e-τ$ flavors. This implies that the claim for a discovery of the NMO will require a careful consideration of the impact of hypothetical NSI.

hep-ph↗

arXiv2019

Physics Potential of ESS$ν$SB in the presence of a Light Sterile Neutrino

ESS$ν$SB is a proposed neutrino super-beam project at the ESS facility. We study the performance of this setup in the presence of a light eV-scale sterile neutrino, considering 540 km baseline with 2 years (8 years) of $ν$ ($\barν$) run-plan. This baseline offers the possibility to work around the second oscillation maximum, providing high sensitivity towards CP-violation (CPV). We explore in detail its capability in resolving CPV generated by the standard CP phase $δ_{13}$, the new CP phase $δ_{14}$, and the octant of $θ_{23}$. We find that the sensitivity to CPV induced by $δ_{13}$ deteriorates noticeably when going from $3ν$ to 4$ν$ case. The two phases $δ_{13}$ and $δ_{14}$ can be reconstructed with a 1$σ$ uncertainty of $\sim15^0$ and $ \sim35^0$ respectively. Concerning the octant of $θ_{23}$, we find poor sensitivity in both $3ν$ and $4ν$ schemes. Our results show that a setup like ESS$ν$SB working around the second oscillation maximum with a baseline of 540 km, performs quite well to explore CPV in 3$ν$ scheme, but it is not optimal for studying CP properties in 3+1 scheme.

hep-ph↗