arXiv subjects

Newton Nath

Publications and source records attributed to Newton Nath.

46 records · Page 3Linked to original sources

arXiv2017

Can nonstandard interactions jeopardize the hierarchy sensitivity of DUNE ?

We study the effect of non-standard interactions (NSIs) on the propagation of neutrinos through the Earth matter and how it affects the hierarchy sensitivity of the DUNE experiment. We emphasize on the special case when the diagonal NSI parameter $ε_{ee} = -1$, nullifying the standard matter effect. We show that, if in addition, CP violation is maximal then this gives rise to an exact intrinsic hierarchy degeneracy in the appearance channel, irrespective of the baseline and energy. Introduction of off-diagonal NSI parameter, $ε_{e τ}$, shifts the position of this degeneracy to a different $ε_{ee}$. Moreover the unknown magnitude and phases of the off-diagonal NSI parameters can give rise to additional degeneracies. Overall, given the current model independent limits on NSI parameters, the hierarchy sensitivity of DUNE can get seriously impacted. However, a more precise knowledge on the NSI parameters, specially $ε_{ee}$, can give rise to an improved sensitivity. Alternatively, if NSI exists in nature, and still DUNE shows hierarchy sensitivity, certain ranges of the NSI parameters can be excluded. Additionally, we briefly discussed the implications of $ε_{ee} = -1$ (in the Earth) on MSW effect in the Sun.

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arXiv2017

Implications of the latest NO$ ν$A results

We discuss the implications of the latest NO$ ν$A results on the measurement of $ν_μ- ν_e$ conversions. From a combined analysis of the disappearance and appearance data, the preferred solutions reported by NO$ ν$A are normal hierarchy (NH) with two degenerate best-fit points one in the lower octant (LO) and $ δ_{CP} = 1.48π$ whereas the other in the higher octant (HO) with $ δ_{CP} = 0.74π$. There is also another solution with inverted hierarchy (IH) which is $0.46 σ$ away from the best-fit. We discuss and quantify the possibility of resolving these degeneracies by inclusion of NO$ ν$A antineutrino runs. We show that if the true solution corresponds to (NH, LO, $\sim 1.48π$) then future data from NO$ ν$A comprising of 3 years of neutrino and 3 years of antineutrino run will be able to resolve the degenerate solutions at 95.45\% C.L. However, if the true solution corresponds to (NH, HO, $\sim 0.74π$), a wrong hierarchy-wrong $ δ_{CP} $ solution remains unresolved even at 68\% C.L. with the full $3ν+3\barν$ projected run of NO$ ν$A. Same is the case if the IH solution turns out to be the true solution. We further show that DUNE (10 kton) will be able to resolve these degenerate solutions at 99.73\% C.L. with only 1 year of neutrino and one year of antineutrino run [1+1] while 5+5 years of DUNE data can resolve the degeneracies at 99.99\% C.L.

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arXiv2017

Phenomenological study of extended seesaw model for light sterile neutrino

We study the zero textures of the Yukawa matrices in the minimal extended type-I seesaw (MES) model which can give rise to $\sim$ eV scale sterile neutrinos. In this model, three right handed neutrinos and one extra singlet $S$ are added to generate a light sterile neutrino. The light neutrino mass matrix for the active neutrinos, $ m_ν$, depends on the Dirac neutrino mass matrix ($ M_{D} $), Majorana neutrino mass matrix ($ M_{R} $) and the mass matrix ($ M_{S} $) coupling the right handed neutrinos and the singlet. The model predicts one of the light neutrino masses to vanish. We systematically investigate the zero textures in $ M_{D} $ and observe that maximum five zeros in $ M_{D} $ can lead to viable zero textures in $ m_ν $. For this study we consider four different forms for $ M_R $ (one diagonal and three off diagonal) and two different forms of $(M_{S})$ containing one zero. Remarkably we obtain only two allowed forms of $ m_ν $ ($m_{eτ} = 0 $ and $m_{ττ}=0$) having inverted hierarchical mass spectrum. We re-analyze the phenomenological implications of these two allowed textures of $m_ν$ in the light of recent neutrino oscillation data. In the context of the MES model, we also express the low energy mass matrix, the mass of the sterile neutrino and the active-sterile mixing in terms of the parameters of the allowed Yukawa matrices. The MES model leads to some extra correlations which disallow some of the Yukawa textures obtained earlier, even though they give allowed one-zero forms of $m_ν$. We show that the allowed textures in our study can be realized in a simple way in a model based on MES mechanism with a discrete Abelian flavor symmetry group $Z_8 \times Z_2$.

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arXiv2017

Generalized degeneracies and their resolution in neutrino oscillation experiments

We discuss a comprehensive way to study the parameter degeneracies in the form of a generalized degeneracy in the neutrino oscillation experiments. First we describe the various degeneracies by considering only neutrino run of the long baseline experiment (LBL), NO$ ν$A. Then we discuss the role of antineutrinos. Later, we present the combined role of T2K (LBL experiment) and ICAL@INO (atmospheric experiment) to resolve these degeneracies. We also discuss the affect of new physics like non-standards interactions (NSI) on the determination of neutrino mass hierarchy in DUNE.

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arXiv2016

What antineutrinos can tell about octant and $δ_{CP}$ in DUNE?

We study the efficiency of DUNE, a next generation long baseline oscillation experiment to resolve two major unknowns in neutrino oscillation physics. These are, octant of $θ_{23}$ (i.e. if $θ_{23}$ is $< 45^\circ$ or $>45^\circ$) and Dirac CP phase $δ_{CP}$. We mainly focus on the role of antineutrinos when they travel 1300 km baseline of DUNE. We observe that for DUNE, the antineutrino runs help to remove parameter degeneracies even in the parameter space where the antineutrino probability suffers from various degeneracies. We study these points in detail and find that, due to enhanced matter effect longer baseline experiments create an increased tension between the neutrino and the antineutrino probabilities which helps to increase total sensitivity in case of combined runs. We also find that, antineutrino run increases overall CP sensitivity due to its ability to abolish octant-$δ_{CP}$ degeneracy.

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arXiv2016

The Physics of antineutrinos in DUNE and resolution of octant degeneracy

We study the capability of the DUNE experiment, which will be the first beam based experiment with a wide band flux profile, to uncover the octant of the leptonic mixing angle $θ_{23}$ (i.e., $θ_{23}$ is $< 45^\circ$ or $>45^\circ$). In this work, we find that for the DUNE baseline of 1300 km, due to enhanced matter effect, the neutrino and antineutrino probabilities are different which creates a tension in the case of combined runs because of which octant sensitivity also can come from disappearance channel. In view of this, we study the physics of antineutrinos in DUNE and explore the role of antineutrinos run that is required to resolve the octant degeneracy at a certain confidence levels.

hep-ex↗

arXiv2016

The physics of antineutrinos in DUNE and determination of octant and $δ_{CP}$

The octant of $θ_{23}$ and $δ_{CP}$ are the two major unknowns in neutrino oscillation physics. The precise determination of octant and $δ_{CP}$ is interlinked through the octant-$δ_{CP}$ degeneracy. In this paper we study the proficiency of the DUNE experiment to determine these parameters, in particular, the role played by the antineutrinos, the broadband nature of the beam and the matter effect. For $P_{μe}$ and $P_{\barμ \bar{e}}$ the octant-$δ_{CP}$ degeneracy occurs at different values of $δ_{CP}$, combination of neutrino and antineutrino runs help to resolve this. However, in regions where neutrinos do not have octant degeneracy adding antineutrino data is expected to decrease the sensitivity because of the degeneracy and reduced statistics. However we find that in case of DUNE baseline, the antineutrino runs help even in parameter space where the antineutrino probabilities suffer from degeneracies. We explore this point in detail and point out that this happens because of the (i) broad-band nature of the beam so that even if there is degeneracy at a particular energy bin, over the whole spectrum the degeneracy may not be there; (ii) the enhanced matter effect due to the comparatively longer baseline which creates an increased tension between the neutrino and the antineutrino probabilities which raises the overall $χ^2$ in case of combined runs. This feature is more prominent for IH since the antineutrino probabilities in this case are much higher than the neutrino probabilities due to matter effects. The main role of antineutrinos in enhancing CP sensitivity is their ability to remove the octant-$δ_{CP}$ degeneracy. However even if one assumes octant to be known the addition of antineutrinos can give enhanced CP sensitivity in some parameter regions due to the tension between the neutrino and antineutrino $χ^2$s.

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arXiv2016

Understanding the Masses and Mixings of One-Zero Textures in 3+1 Scenario

We present a detailed analysis and phenomenological consequences of neutrino mass matrix, $M_ν$, with one-zero texture in the flavor basis where the active neutrino sector is extended by one sterile neutrino (3+1 case). In particular, our aim is to explore behaviour of the sterile mixing parameters in detail when one of the elements of the neutrino mass matrix goes to zero. To study this, we consider two distinct mass spectrum of the active neutrinos: (i) completely hierarchical mass spectrum with a vanishing neutrino mass and (ii) completely quasidegenerate mass spectrum. In 3+1 scenario, the low energy neutrino mass matrix, $M_ν$, is a $4 \times 4$ matrix and has 10 independent elements. Thus it can have 10 possible one-zero textures. From the earlier studies it can be inferred that, if one assumes one vanishing neutrino mass, then only seven of these $M_ν$ are phenomenologically allowed by the current neutrino oscillation data. On the other hand, if the neutrinos are quasidegenerate then there are eight phenomenologically viable one-zero textures. In this present work, we study the correlations between the sterile mixing parameters for each of these allowed textures for both mass spectrum and also their implications on the effective Majorana mass.

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arXiv2016

Neutrino masses and mixing in $A_5$ with flavour antisymmetry

We discuss consequences of assuming that the (Majorana) neutrino mass matrix $M_ν$ and the charged lepton mass matrix $M_l$ satisfy, $S_ν^T M_νS_ν=-M_ν~,T_l^\dagger M_lM_l^\dagger T_l=M_lM_l^\dagger$ with respect to some discrete groups $S_ν,T_l$ contained in $A_5$. These assumptions lead to a neutrino mass spectrum with two degenerate and one massless neutrino and also constrain mixing among them. We derive possible mixing patterns following from the choices $S_ν=Z_2,~ Z_2\times Z_2$ and $T_l=Z_2, ~ Z_2\times Z_2, ~Z_3, ~Z_5$ as subgroups of $A_5$. One predicts the maximal atmospheric neutrino mixing angle $θ_{23}$ and $μ$-$τ$ reflection symmetry in large number of cases but it is also possible to obtain non-maximal values for $θ_{23}$. Only the third column of the neutrino mixing matrix can be obtained at the leading order due to degeneracy in masses of two of the neutrinos. We take up a specific example within $A_5$ group and identify Higgs vacuum expectations values which realize the above assumptions. Non-leading terms present in this example are shown to lead to splitting among degenerate pairs and a consistent description of both neutrino masses and mixing angles.

hep-ph↗

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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