arXiv subjects

Monojit Ghosh

Publications and source records attributed to Monojit Ghosh.

At least 55 records · Page 3Linked to original sources

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 $m_ν$.

hep-ph↗

arXiv2017

Effect of systematics in the T2HK, T2HKK, and DUNE experiments

T2HK and T2HKK are the proposed extensions of the of T2K experiments in Japan and DUNE is the future long-baseline program of Fermilab. All these three experiments will use extremely high beam power and large detector volumes to observe neutrino oscillation. Because of the large statistics, these experiments will be highly sensitive to systematics. Thus a small change in the systematics can cause a significant change in their sensitivities. To understand this, we do a comparative study of T2HK, T2HKK and DUNE with respect to their systematic errors. Specifically we study the effect of the systematics in the determination of neutrino mass hierarchy, octant of the mixing angle $θ_{23}$ and $δ_{CP}$ in the standard three flavor scenario and also analyze the role of systematic uncertainties in constraining the parameters of the nonstandard interactions in neutrino propagation. Taking the overall systematics for signal and background normalization, we quantify how the sensitivities of these experiments change if the systematics are varied from $1\%$ to $7\%$.

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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 $δ_{\mathrm{CP}}$.

hep-ph↗

arXiv2017

Physics Potential of the ICAL detector at the India-based Neutrino Observatory (INO)

The upcoming 50 kt magnetized iron calorimeter (ICAL) detector at the India-based Neutrino Observatory (INO) is designed to study the atmospheric neutrinos and antineutrinos separately over a wide range of energies and path lengths. The primary focus of this experiment is to explore the Earth matter effects by observing the energy and zenith angle dependence of the atmospheric neutrinos in the multi-GeV range. This study will be crucial to address some of the outstanding issues in neutrino oscillation physics, including the fundamental issue of neutrino mass hierarchy. In this document, we present the physics potential of the detector as obtained from realistic detector simulations. We describe the simulation framework, the neutrino interactions in the detector, and the expected response of the detector to particles traversing it. The ICAL detector can determine the energy and direction of the muons to a high precision, and in addition, its sensitivity to multi-GeV hadrons increases its physics reach substantially. Its charge identification capability, and hence its ability to distinguish neutrinos from antineutrinos, makes it an efficient detector for determining the neutrino mass hierarchy. In this report, we outline the analyses carried out for the determination of neutrino mass hierarchy and precision measurements of atmospheric neutrino mixing parameters at ICAL, and give the expected physics reach of the detector with 10 years of runtime. We also explore the potential of ICAL for probing new physics scenarios like CPT violation and the presence of magnetic monopoles.

physics.ins-det↗

arXiv2017

Study of parameter degeneracy and hierarchy sensitivity of NO$ν$A in presence of sterile neutrino

The first hint of the neutrino mass hierarchy is believed to come from the long-baseline experiment NO$ν$A. Recent results from the NO$ν$A shows a mild preference towards the CP phase $δ_{13} = -90^\circ$ and normal hierarchy. Fortunately this is the favorable area of the parameter space which does not suffer from the hierarchy-$δ_{13}$ degeneracy and thus NO$ν$A can have good hierarchy sensitivity for this true combination of hierarchy and $δ_{13}$. Apart from the hierarchy-$δ_{13}$ degeneracy there is also the octant-$δ_{13}$ degeneracy. But this does not affect the favorable parameter space of NO$ν$A as this degeneracy can be resolved with a balanced neutrino and antineutrino run. However, ff we consider the existence of a light sterile neutrino then there may be additional degeneracies which can spoil the hierarchy sensitivity of NO$ν$A even in the favorable parameter space. In the present work we find that apart from the degeneracies mentioned above, there are additional hierarchy and octant degeneracies that appear with the new phase $δ_{14}$ in the presence of a light sterile neutrino in the eV scale. In contrast to the hierarchy and octant degeneracies appearing with $δ_{13}$, the parameter space for hierarchy-$δ_{14}$ degeneracy is different in neutrinos and antineutrinos though the octant-$δ_{14}$ degeneracy behaves similarly in neutrinos and antineutrinos. We study the effect of these degeneracies on the hierarchy sensitivity of NO$ν$A for the true normal hierarchy.

hep-ph↗

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 $Z_8 \times Z_2$.

hep-ph↗

arXiv2017

Why T2K should run in dominant neutrino mode to discover CP violation ?

The first hint of the leptonic CP phase $δ_{CP}=-90^\circ$ has already came from the long-baseline neutrino oscillation experiment T2K. This hint is derived from the neutrino data of T2K and currently it is running in the antineutrino mode. In this work we ask the question what should be the proportion of neutrino and antineutrino running of the T2K experiment to discover CP violation in the leptonic sector.

hep-ph↗

arXiv2017

Sensitivity of the T2HKK experiment to the non-standard interaction

If the flavor dependent non-standard interactions (NSI) in neutrino propagation exist, then the matter effect is modified and the modification is parametrized by the dimensionless parameter $ε_{αβ}~(α,β=e, μ, τ)$. In this paper we discuss the sensitivity of the T2HKK experiment, whose possibility is now seriously discussed as a future extension of the T2K experiment, to such NSI. On the assumption that $ε_{αμ}=0~(α=e, μτ)$ and $ε_{ττ}=|ε_{eτ}|/(1+ε_{ee})$, which are satisfied by other experiments to a good approximation, we find that, among the possible off-axis flux configurations of $1.3^\circ$, $1.5^\circ$, $2.0^\circ$ and $2.5^\circ$, the case of the off-axis angle $1.3^\circ$ gives the highest sensitivity to $ε_{ee}$ and $|ε_{eτ}|$. Our results show that the $1.3^\circ$ off-axis configuration can exclude NSI for $|ε_{ee}|\gtrsim 1$ or $|ε_{eτ}|\gtrsim 0.2$ at 3$σ$. We also find that in the presence of NSI, T2HKK (for the off-axis angle $1.3^\circ$) has better sensitivity to the two CP phases ($δ_{CP}$ and arg($ε_{e τ}$)) than DUNE. This is because of the synergy between the two detectors i.e., one at Kamioka and one at Korea. T2HKK has better sensitivity to the CP phases than the atmospheric neutrino experiment at Hyperkamiokande in inverted hierarchy, but in normal hierarchy the atmospheric neutrino experiment has the best sensitivity to the CP phases.

hep-ph↗

arXiv2017

Complementarity Between Hyperkamiokande and DUNE in Determining Neutrino Oscillation Parameters

In this work we investigate the sensitivity to the neutrino mass hierarchy, the octant of the mixing angle $θ_{23}$ and the CP phase $δ_{CP}$ in the future long-baseline experiments T2HK and DUNE as well as in the atmospheric neutrino observation at Hyperkamiokande (HK). We show for the first time that the sensitivity is enhanced greatly if we combine these three experiments. Our results show that the hierarchy sensitivity of both T2HK and HK are limited due to the presence of parameter degeneracy. But this degeneracy is removed when T2HK and HK are added together. With T2HK+HK (DUNE), the neutrino mass hierarchy can be determined at least at $ 5 σ$ (8 $σ$) C.L. for any value of true $δ_{CP}$. With T2HK+HK+DUNE the significance of the mass hierarchy increases to almost 15 $σ$ for the unfavorable value of $δ_{CP}$. For these combined setup, octant can be resolved except $43.5^\circ < θ_{23} < 48^\circ$ at $5σ$ C.L for both the hierarchies irrespective of the value of $δ_{CP}$. The significance of CP violation is around 10 $σ$ C.L. for $δ_{CP} \sim \pm 90^\circ$. Apart from that these combined facility has the capability to discover CP violation for at least $68\%$ fraction of the true $δ_{CP}$ values at $5 σ$ for any value of true $θ_{23}$. We also find that, with combination of all these three, the precision of $Δm^2_{\rm eff}$, $\sin^2θ_{23}$ and $δ_{CP}$ becomes 0.3%, 2% and 20% respectively. We also clarify how the octant degeneracy occurs in the HK atmospheric neutrino experiment.

hep-ph↗

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.

hep-ph↗

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.

hep-ph↗

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.

hep-ph↗

arXiv2016

Should T2K run in dominant neutrino mode to detect CP violation ?

The main aim of the T2K experiment in Japan is to discover CP violation in the leptonic sector by measuring the Dirac phase $δ_{CP}$. For that purpose T2K has already started collecting data in both neutrino and antineutrino mode. But in this work we will show that, in T2K the main role of the antineutrinos is to resolve the octant degeneracy. If the octant is known then the pure neutrino run of T2K is capable to give the maximum CP sensitivity. On the other hand in the experiment like NO$ν$A, antineutrinos are still useful even when octant is known. Thus we propose that let T2K run in the dominant neutrino mode whereas the antineutrino component of the other experiments can resolve the octant degeneracy in T2K. As an example we show that if T2K is combined with the experiments NO$ν$A and ICAL@INO, then T2K will have the potential to discover CP violation with maximum sensitivity in the dominant neutrino mode.

hep-ph↗

arXiv2016

Complementarity Between Hyperkamiokande and DUNE

In this talk we present our results on the sensitivity to the neutrino mass hierarchy, the octant of the mixing angle and the CP phase in the future long baseline experiments T2HK and DUNE as well as in the atmospheric neutrino observation at Hyperkamiokande (HK).

hep-ph↗

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.

hep-ph↗

arXiv2016

Is nonstandard interaction a solution to the three neutrino tensions?

In this work we present a scenario in which a nonstandard interaction in neutrino propagation can explain the three major tensions in the neutrino oscillation data at present. These tensions are: (i) a non-zero best-fit value of the non-standard oscillation parameters in the the global analysis of the solar and KamLAND data which rules out the standard oscillation scenario at $90\%$ C.L, (ii) the measurement of the non-maximal value of $θ_{23}$ by NO$ν$A which excludes the maximal mixing at $2.5 σ$ C.L. and (iii) a discrepancy in the $θ_{13}$ measurement by T2K which has a tension with the reactor best-fit value of $\sin^2θ_{13}=0.021$ at $90\%$ C.L. Our results show that all these three above mentioned anomalies can be explained if one assumes the existence of the non-standard interactions in neutrino propagation with $θ_{23}=45^\circ$ and $\sin^2θ_{13}=0.021$ in the case of normal hierarchy. In our scenario the phase of $ε_{eτ}$ is zero and the most favorable value of the Dirac CP phase is approximately $255^\circ$.

hep-ph↗

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.

hep-ph↗