arXiv subjects

Sabya Sachi Chatterjee

Publications and source records attributed to Sabya Sachi Chatterjee.

31 records · Page 2Linked to original sources

arXiv2019

Neutrino Non-Standard Interactions: A Status Report

This report summarizes the present status of neutrino non-standard interactions (NSI). After a brief overview, several aspects of NSIs are discussed, including connection to neutrino mass models, model-building and phenomenology of large NSI with both light and heavy mediators, NSI phenomenology in both short- and long-baseline neutrino oscillation experiments, neutrino cross-sections, complementarity of NSI with other low- and high-energy experiments, fits with neutrino oscillation and scattering data, DUNE sensitivity to NSI, effective field theory of NSI, as well as the relevance of NSI to dark matter and cosmology. We also discuss the open questions and interesting future directions that can be pursued by the community at large. This report is based on talks and discussions during the Neutrino Theory Network NSI workshop held at Washington University in St. Louis from May 29-31, 2019 (https://indico.cern.ch/event/812851/)

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arXiv2019

Enhancing Sensitivity to Non-Standard Neutrino Interactions at INO combining muon and hadron information

The neutral current non-standard interactions (NSI's) of neutrino with matter fermions while propagating through long distances inside the Earth matter can give rise to the extra matter potentials apart from the standard MSW potential due to the $W$-mediated interactions in matter. In this paper, we explore the impact of flavor violating neutral current NSI parameter $\varepsilon_{μτ}$ in the oscillation of atmospheric neutrino and antineutrino using the 50 kt magnetized ICAL detector at INO. We find that due to non-zero $\varepsilon_{μτ}$, $ν_μ\rightarrowν_μ$ and $\barν_μ\rightarrow\barν_μ$ transition probabilities get modified substantially at higher energies and longer baselines, where vacuum oscillation dominates. We estimate the sensitivity of the ICAL detector for various choices of binning schemes and observables. The most optimistic bound on $\varepsilon_{μτ}$ that we obtain is $-0.01 < \varepsilon_{μτ} < 0.01 $ at 90$\%$ C.L. using 500 kt$\cdot$yr exposure and considering $E_μ,\, \cosθ_μ,\,E'_{\rm had}$ as observables in their ranges [1, 21] GeV, [-1, 1], and [0, 25] GeV respectively. For the first time we show that the charge identification capability of the ICAL detector is crucial to set stringent constraints on $\varepsilon_{μτ}$. We also show that when we marginalize over $\varepsilon_{μτ}$ in fit in its range of -0.1 to 0.1, the mass hierarchy sensitivity deteriorates by 10$\%$ to 20$\%$ depending on the analysis mode, and the precision measurements of atmospheric parameters remain quite robust at the ICAL detector.

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arXiv2018

Signatures of a Light Sterile Neutrino in T2HK

We investigate the performance of T2HK in the presence of a light eV scale sterile neutrino. We study in detail its influence in resolving fundamental issues like mass hierarchy, CP-violation (CPV) induced by the standard CP-phase $δ_{13}$ and new CP-phase $δ_{14}$, and the octant ambiguity of $θ_{23}$. We show for the first time in detail that due to the impressive energy reconstruction capabilities of T2HK, the available spectral information plays an important role to enhance the mass hierarchy discovery reach of this experiment in 3$ν$ framework and also to keep it almost intact even in $4ν$ scheme. This feature is also of the utmost importance in establishing the CPV due to $δ_{14}$. As far as the sensitivity to CPV due to $δ_{13}$ is concerned, it does not change much going from $3ν$ to 4$ν$ case. We also examine the reconstruction capability of the two phases $δ_{13}$ and $δ_{14}$, and find that the typical 1$σ$ uncertainty on $δ_{13}$ ($δ_{14}$) in T2HK is $\sim15^0$ ($30^0$). While determining the octant of $θ_{23}$, we face a complete loss of sensitivity for unfavorable combinations of unknown $δ_{13}$ and $δ_{14}$.

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arXiv2018

Addressing Neutrino Mixing Models with DUNE and T2HK

We consider schemes of neutrino mixing arising within the discrete symmetry approach to the well-known flavour problem. We concentrate on $3ν$ mixing schemes in which the cosine of the Dirac CP violation phase $δ_\mathrm{CP}$ satisfies a sum rule by which it is expressed in terms of three neutrino mixing angles $θ_{12}$, $θ_{23}$, and $θ_{13}$, and a fixed real angle $θ^ν_{12}$, whose value depends on the employed discrete symmetry and its breaking. We consider five underlying symmetry forms of the neutrino mixing matrix: bimaximal (BM), tri-bimaximal (TBM), golden ratio A (GRA) and B (GRB), and hexagonal (HG). For each symmetry form, the sum rule yields specific prediction for $\cosδ_\mathrm{CP}$ for fixed $θ_{12}$, $θ_{23}$, and $θ_{13}$. In the context of the proposed DUNE and T2HK facilities, we study (i) the compatibility of these predictions with present neutrino oscillation data, and (ii) the potential of these experiments to discriminate between various symmetry forms.

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arXiv2017

Probing atmospheric mixing and leptonic CP violation in current and future long baseline oscillation experiments

We perform realistic simulations of the current and future long baseline experiments such as T2K, NO$ν$A, DUNE and T2HK in order to determine their ultimate potential in probing neutrino oscillation parameters. We quantify the potential of these experiments to underpin the octant of the atmospheric angle $θ_{23}$ as well as the value and sign of the CP phase $δ_{CP}$.

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arXiv2017

Cornering the revamped BMV model with neutrino oscillation data

Using the latest global determination of neutrino oscillation parameters from~\cite{deSalas:2017kay} we examine the status of the simplest revamped version of the BMV (Babu-Ma-Valle) model, proposed in~\cite{Morisi:2013qna}. The model predicts a striking correlation between the "poorly determined" atmospheric angle $θ_{23}$ and CP phase $δ_{CP}$, leading to either maximal CP violation or none, depending on the preferred $θ_{23}$ octants. We determine the allowed BMV parameter regions and compare with the general three-neutrino oscillation scenario. We show that in the BMV model the higher octant is possible only at $99\%$ C.L., a stronger rejection than found in the general case. By performing quantitative simulations of forthcoming DUNE and T2HK experiments, using only the four "well-measured" oscillation parameters and the indication for normal mass ordering, we also map out the potential of these experiments to corner the model. The resulting global sensitivities are given in a robust form, that holds irrespective of the true values of the oscillation parameters.

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arXiv2017

Resolving the atmospheric octant by an improved measurement of the reactor angle

Taking into account the current global information on neutrino oscillation parameters we forecast the capabilities of future long baseline experiments such as DUNE and T2HK in settling the atmospheric octant puzzle. We find that a good measurement of the reactor angle $θ_{13}$ plays a key role in fixing the octant of the atmospheric angle $θ_{23}$ with such future accelerator neutrino studies.

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arXiv2017

Can we measure $θ_{23}$ octant in 3+1 scheme?

Current 3$ν$ global fits predict two degenerate solutions for $θ_{23}$: one lies in lower octant ($θ_{23} <π/4$), and the other belongs to higher octant ($θ_{23} >π/4$). Here, we study how the measurement of $θ_{23}$ octant would be affected in the upcoming Deep Underground Neutrino Experiment (DUNE) if there exist a light eV-scale sterile neutrino. We show that in 3+1 scheme, a new interference term in $ν_μ\to ν_e$ oscillation probability can spoil the chances of measuring $θ_{23}$ octant completely.

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arXiv2017

Octant of $θ_{23}$ in danger with a light sterile neutrino

Present global fits of world neutrino data hint towards non-maximal $θ_{23}$ with two nearly degenerate solutions, one in the lower octant ($θ_{23} <π/4$), and the other in the higher octant ($θ_{23} >π/4$). This octant ambiguity of $θ_{23}$ is one of the fundamental issues in the neutrino sector, and its resolution is a crucial goal of next-generation long-baseline (LBL) experiments. In this letter, we address for the first time, the impact of a light eV-scale sterile neutrino towards such a measurement, taking the Deep Underground Neutrino Experiment (DUNE) as a case study. In the so-called 3+1 scheme involving three active and one sterile neutrino, the $ν_μ\to ν_e$ transition probability probed in the LBL experiments acquires a new interference term via active-sterile oscillations. We find that this novel interference term can mimic a swap of the $θ_{23}$ octant, even if one uses the information from both neutrino and antineutrino channels. As a consequence, the sensitivity to the octant of $θ_{23}$ can be completely lost and this may have serious implications in our understanding of neutrinos from both the experimental and theoretical perspectives.

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arXiv2016

Physics Reach of DUNE with a Light Sterile Neutrino

We investigate the implications of one light eV scale sterile neutrino on the physics potential of the proposed long-baseline experiment DUNE. If the future short-baseline experiments confirm the existence of sterile neutrinos, then it can affect the mass hierarchy (MH) and CP-violation (CPV) searches at DUNE. The MH sensitivity still remains above 5$σ$ if the three new mixing angles ($θ_{14}, θ_{24}, θ_{34}$) are all close to $θ_{13}$. In contrast, it can decrease to 4$σ$ if the least constrained mixing angle $θ_{34}$ is close to its upper limit $\sim 30^0$. We also assess the sensitivity to the CPV induced both by the standard CP-phase $δ_{13} \equiv δ$, and the new CP-phases $δ_{14}$ and $δ_{34}$. In the 3+1 scheme, the discovery potential of CPV induced by $δ_{13}$ gets deteriorated compared to the 3$ν$ case. In particular, the maximal sensitivity (reached around $δ_{13}$ $\sim$ $\pm$ $90^0$) decreases from $5σ$ to $4σ$ if all the three new mixing angles are close to $θ_{13}$. It can further diminish to almost $3σ$ if $θ_{34}$ is large ($\sim 30^0$). The sensitivity to the CPV due to $δ_{14}$ can reach 3$σ$ for an appreciable fraction of its true values. Interestingly, $θ_{34}$ and its associated phase $δ_{34}$ can influence both the $ν_e$ appearance and $ν_μ$ disappearance channels via matter effects, which in DUNE are pronounced. Hence, DUNE can also probe CPV induced by $δ_{34}$ provided $θ_{34}$ is large. We also reconstruct the two phases $δ_{13}$ and $δ_{14}$. The typical 1$σ$ uncertainty on $δ_{13}$ ($δ_{14}$) is $\sim20^0$ ($30^0$) if $θ_{34} =0$. The reconstruction of $δ_{14}$ (but not that of $δ_{13}$) degrades if $θ_{34}$ is large.

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arXiv2016

Degeneracy between $θ_{23}$ octant and neutrino non-standard interactions at DUNE

We expound in detail the degeneracy between the octant of $θ_{23}$ and flavor-changing neutral-current non-standard interactions (NSI's) in neutrino propagation, considering the Deep Underground Neutrino Experiment (DUNE) as a case study. In the presence of such NSI parameters involving the $e-μ$ ($\varepsilon_{eμ}$) and $e-τ$ ($\varepsilon_{eτ}$) flavors, the $ν_μ\to ν_e$ and $\barν_μ\to \barν_e$ appearance probabilities in long-baseline experiments acquire an additional interference term, which depends on one new dynamical CP-phase $ϕ_{eμ/eτ}$. This term sums up with the well-known interference term related to the standard CP-phase $δ$ creating a source of confusion in the determination of the octant of $θ_{23}$. We show that for values of the NSI coupling (taken one at-a-time) as small as $few\,\%$ (relative to the Fermi coupling constant $G_{\mathrm F}$), and for unfavorable combinations of the two CP-phases $δ$ and $ϕ_{eμ/eτ}$, the discovery potential of the octant of $θ_{23}$ gets completely lost.

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arXiv2016

Discovery Potential of T2K and NOvA in the Presence of a Light Sterile Neutrino

We study the impact of one light sterile neutrino on the prospective data expected to come from the two presently running long-baseline experiments T2K and NOvA when they will accumulate their full planned exposure. Introducing for the first time, the bi-probability representation in the 4-flavor framework, commonly used in the 3-flavor scenario, we present a detailed discussion of the behavior of the numu to nue and numubar to nuebar transition probabilities in the 3+1 scheme. We also perform a detailed sensitivity study of these two experiments (both in the stand-alone and combined modes) to assess their discovery reach in the presence of a light sterile neutrino. For realistic benchmark values of the mass-mixing parameters (as inferred from the existing global short-baseline fits), we find that the performance of both these experiments in claiming the discovery of the CP-violation induced by the standard CP-phase delta13 equivalent to delta, and the neutrino mass hierarchy get substantially deteriorated. The exact loss of sensitivity depends on the value of the unknown CP-phase delta14. Finally, we estimate the discovery potential of total CP-violation (i.e., induced simultaneously by the two CP-phases delta13 and delta14), and the capability of the two experiments of reconstructing the true values of such CP-phases. The typical (1 sigma level) uncertainties on the reconstructed phases are approximately 40 degree for delta13 and 50 degree for delta14.

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arXiv2016

Exploring Flavor-Dependent Long-Range Forces in Long-Baseline Neutrino Oscillation Experiments

The Standard Model gauge group can be extended with minimal matter content by introducing anomaly free U(1) symmetry, such as $L_e-L_μ$ or $L_e-L_τ$. If the neutral gauge boson corresponding to this abelian symmetry is ultra-light, then it will give rise to flavor-dependent long-range leptonic force, which can have significant impact on neutrino oscillations. For an instance, the electrons inside the Sun can generate a flavor-dependent long-range potential at the Earth surface, which can suppress the $ν_μ \to ν_e$ appearance probability in terrestrial experiments. The sign of this potential is opposite for anti-neutrinos, and affects the oscillations of (anti-)neutrinos in different fashion. This feature invokes fake CP-asymmetry like the SM matter effect and can severely affect the leptonic CP-violation searches in long-baseline experiments. In this paper, we study in detail the possible impacts of these long-range flavor-diagonal neutral current interactions due to $L_e-L_μ$ symmetry, when (anti-)neutrinos travel from Fermilab to Homestake (1300 km) and CERN to Pyhäsalmi (2290 km) in the context of future high-precision superbeam facilities, DUNE and LBNO respectively. If there is no signal of long-range force, DUNE (LBNO) can place stringent constraint on the effective gauge coupling $α_{eμ} < 1.9 \times 10^{-53}~(7.8 \times 10^{-54})$ at 90% C.L., which is almost 30 (70) times better than the existing bound from the Super-Kamiokande experiment. We also observe that if $α_{eμ} \geq 2 \times 10^{-52}$, the CP-violation discovery reach of these future facilities vanishes completely. The mass hierarchy measurement remains robust in DUNE (LBNO) if $α_{eμ} < 5 \times 10^{-52}~(10^{-52})$.

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