arXiv subjects

Sandhya Choubey

Publications and source records attributed to Sandhya Choubey.

At least 127 records · Page 7Linked to original sources

arXiv2002

Neutrino decay confronts the SNO data

We investigate the status of the neutrino decay solution to the solar neutrino problem in the context of the recent results from Sudbury Neutrino Observatory (SNO). We present the results of global $χ^2$-analysis for both two and three generation cases with one of the mass states being allowed to decay and include the effect of both decay and mixing. We find that the Large Mixing Angle (LMA) region which is the currently favoured solution of the solar neutrino problem is affected significantly by decay. We present the allowed areas in the $Δm^2-\tan^2θ$ plane for different allowed values of $α$ and examine how these areas change with the inclusion of decay. We obtain bounds on the decay constant $α$ in this region which implies a rest frame life time $τ_0/m_{2} > 8.7 \times 10^{-5}$ sec/eV for the unstable neutrino state. We conclude that the arrival of the neutral current results from SNO further disfavors the neutrino decay solution to the solar neutrino problem leaving a very small window for the decay constant $α$ which could still be allowed.

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arXiv2002

SNO and the solar neutrino problem

We study the implication of the first neutral current (NC) data from SNO. We perform model independent and model dependent analyses of the solar neutrino data. The inclusion of the first SNO NC data in the model independent analysis determines the allowed ranges of $^{8}{B}$ flux normalization and the $ν_e$ survival probability more precisely than what was possible from the SK and SNO CC combination. Transitions to pure sterile states are seen to be hugely disfavored however transition to ``mixed'' states are still viable with a probability of finding about 30% sterile component in the resultant beam at $1σ$. We perform global $ν_e-ν_{active}$ oscillation analyses of solar neutrino data including the recent SNO results. LMA emerges as a huge favorite while LOW appears at the $3σ$ level. All the other solutions are disfavored at $3σ$ while SMA is virtually ruled out. Maximal mixing is disfavored at $3σ$. We explore in some details the reasons for the incompatibility of the maximal mixing solution and the LOW solution with the global solar neutrino data.

hep-ph↗

arXiv2002

Implications of the first neutral current data from SNO for Solar Neutrino Oscillation

We perform model independent and model dependent analyses of solar neutrino data including the neutral current event rate from SNO. The inclusion of the first SNO NC data in the model independent analysis determines the allowed ranges of $^{8}{B}$ flux normalisation and the $ν_e$ survival probability more precisely than what was possible from the SK and SNO CC combination. We perform global $ν_e-ν_{active}$ oscillation analyses of solar neutrino data using the NC rate instead of the SSM prediction for the $^{8}{B}$ flux, in view of the large uncertainty in the latter. The LMA gives the best solution, while the LOW solution is allowed only at the $3σ$ level.

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arXiv2002

What can the SNO Neutral Current Rate teach us about the Solar Neutrino Anomaly

We investigate how the anticipated neutral current rate from $SNO$ will sharpen our understanding of the solar neutrino anomaly. Quantitative analyses are performed with representative values of this rate in the expected range of $0.8 - 1.2$. This would provide a $5 - 10 σ$ signal for $ν_e$ transition into a state containing an active neutrino component. Assuming this state to be purely active one can estimate both the $^8B$ neutrino flux and the $ν_e$ survival probability to a much higher precision than currently possible. Finally the measured value of the $NC$ rate will have profound implications for the mass and mixing parameters of the solar neutrino oscillation solution.

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arXiv2002

A minimal three generation seesaw scenario for LSND

We show that in the minimal three generation seesaw models for neutrinos, the presence of leptonic $(L_e+L_μ-L_τ)\times S_2$ symmetry leads to one of the right handed neutrinos remaining massless. This state can then be identified with the sterile neutrino required for a simultaneous understanding of solar, atmospheric and LSND observations. We present a gauge model where the presence of higher dimensional operators originating from Planck scale physics lead to a realistic 2+2 mixed scenario that fits all oscillation data. The model predicts a range for the mixing angle $U_{e3}$ and an effective mass for neutrinos emitted in tritium decay, which can be used to test this model.

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arXiv2002

Three Generation Neutrino Oscillation Parameters after SNO

We examine the solar neutrino problem in the context of the realistic three neutrino mixing scenario including the SNO charged current (CC) rate. The two independent mass squared differences $Δm^2_{21}$ and $Δm^2_{31} \approx Δm^2_{32}$ are taken to be in the solar and atmospheric ranges respectively. We incorporate the constraints on $Δ$m$^2_{31}$ as obtained by the SuperKamiokande atmospheric neutrino data and determine the allowed values of $Δm^2_{21}$, $θ_{12}$ and $θ_{13}$ from a combined analysis of solar and CHOOZ data. Our aim is to probe the changes in the values of the mass and mixing parameters with the inclusion of the SNO data as well as the changes in the two-generation parameter region obtained from the solar neutrino analysis with the inclusion of the third generation. We find that the inclusion of the SNO CC rate in the combined solar + CHOOZ analysis puts a more restrictive bound on $θ_{13}$. Since the allowed values of $θ_{13}$ are constrained to very small values by the CHOOZ experiment there is no qualitative change over the two generation allowed regions in the $Δm^2_{21} - \tan^2 θ_{12}$ plane. The best-fit comes in the LMA region and no allowed area is obtained in the SMA region at 3$σ$ level from combined solar and CHOOZ analysis.

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arXiv2002

Viability of bi-maximal solution of the Zee mass matrix

We know $L_e-L_μ-L_τ$ symmetry gives $m^2_1= m^2_2 >> m^2_3$ pattern in Zee model. $Δm^2_\odot$ emerges from a small breaking of this symmetry. Because this symmetry is broken very weakly $θ_\odot$ does not deviate much from $\tan^2 θ_\odot=1$ which is its value in the symmetric limit. This gives a mismatch with LMA solution where mixing is large but not exactly maximal. We confront this property of Zee mass matrix by phenomenologically analyzing recent results from solar and atmospheric neutrino oscillation experiments at various confidence levels. We conclude that LOW type solution is compatible with the Zee mass matrix at 99% confidence level when atmospheric neutrino deficit is explained by maximal $ν_μ\leftrightarrow ν_τ$ oscillation. Thus the minimal version of the Zee model even though disfavored by the LMA type or VO type solutions, is compatible with LOW type solution of solar neutrino problem.

hep-ph↗

arXiv2001

Neutrinos and their flavor mixing in nuclear astrophysics

In this thesis we explore the implications of neutrino oscillations in the context of the solar neutrino data, the atmospheric neutrino data and results from the terrestrial accelerator/reactor neutrino oscillation experiments. We perform comprehensive $χ^2$ analysis for the global solar neutrino data including SNO and present our results for two flavor $ν_e-ν_{active}$ and $ν_e-ν_{sterile}$ oscillations. We explore the apparent conflict between the flat SK spectrum and the non-monotonic energy dependence of the solar neutrino survival probability inferred from the global data on total rates. We analyze the SK atmospheric neutrino data in the framework of two and three generations. For the three-generation analysis we simultaneously take into account the results of the terrestrial neutrino experiments. We consider the possibility of unstable neutrinos and explore the viability of this decay model as a solution to the atmospheric neutrino anomaly. We make quantitative predictions for the number of events recorded in the water Cerenkov detectors due a galactic supernova and examine the signatures of neutrino mass and mixing in the resultant neutrino signal.

hep-ph↗

arXiv2001

Global oscillation analysis of solar neutrino data with helioseismically constrained fluxes

A seismic model for the Sun calculated using the accurate helioseismic data predicts a lower $^{8}{B}$ neutrino flux as compared to the standard solar model (SSM). However, there persists a discrepancy between the predicted and measured neutrino fluxes and it seems necessary to invoke neutrino oscillations to explain the measurements. In this work, we have performed a global, unified oscillation analysis of the latest solar neutrino data (including the results of SNO charged current rate) using the seismic model fluxes as theoretical predictions. We determine the best-fit values of the neutrino oscillation parameters and the $χ^2_{\mathrm min}$ for both $ν_e-ν_{\mathrm active}$ and $ν_e -ν_{\mathrm sterile}$ cases and present the allowed parameter regions in the $Δm^2 - \tan^2 θ$ plane for $ν_e-ν_{\mathrm active}$ transition. The results are compared with those obtained using the latest SSM by Bahcall and his collaborators.

hep-ph↗

arXiv2001

Energy Independent Solution to the Solar Neutrino Anomaly including the SNO data

The global data on solar neutrino rates and spectrum, including the SNO charged current rate, can be explained by LMA, LOW or the energy independent solution -- corresponding to near-maximal mixing. All the three favour a mild upward renormalisation of the Cl rate. A mild downward shift of the $B$ neutrino flux is favoured by the energy independent and to a lesser extent the LOW solution, but not by LMA. Comparison with the ratio of SK elastic and SNO charged current scattering rates favours the LMA over the other two solutions, but by no more than $1.5σ$.

hep-ph↗

arXiv2001

Impact of the first SNO results on Neutrino Mass and Mixing

We investigate the implications of the SNO charged-current (CC) and electron scattering (ES) measurements of solar \br neutrino fluxes for neutrino mass and mixing parameters by performing a global and unified $χ^2$ analysis of the solar neutrino data in the framework of two neutrino mixing. We consider both $ν_e -ν_{active}$ and $ν_e -ν_{sterile}$ solutions and perform (i) analysis of the total rates data of Cl, Ga, SK and SNO experiments and (ii) global analysis including the total rates data, the recoil electron spectrum data of SK and the CC spectrum observed at SNO. For the $ν_e-ν_{active}$ case the inclusion of the SNO results in the analysis of the total rates reduces(enhances) the goodness-of-fit (GOF) of the SMA(LMA) solution. The flat spectrum observed at SK further favours the LMA solution over the SMA solution and no allowed area is obtained in the SMA region at 3$σ$ level from the global analysis. For the $ν_e -ν_{sterile}$ case, with the inclusion of the SNO results, all the solutions are disfavoured with a probability of more than 99% from the total rates analysis while for the global analysis the GOF of these become much worse.

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arXiv2001

Reviving the energy independent suppression of the solar neutrino flux

We explore the possibility of an energy independent suppression of the solar neutrino flux in the context of the recent SuperKamiokande data. From a global analysis of the rate and spectrum data, this scenario is allowed at only 14% probability with the observed Cl rate. If we allow for a 20% upward renormalisation of the Cl rate along with a downward renormalisation of the $B$ neutrino flux then the fit improves considerably to a probability of $\sim 50%$. We compare the quality of these fits with those of the MSW solutions. These renormalisations are also found to improve the quality of the fits with MSW solutions and enlarge the allowed region of their validity in the parameter space substantially. Over much of this enlarged region the matter effects on the suppression of the solar neutrino flux are found to be very weak, so that the solutions become practically energy independent.

hep-ph↗

arXiv2001

A three generation oscillation analysis of the Super-Kamiokande atmospheric neutrino data beyond one mass scale dominance approximation

In this paper we do a three-generation oscillation analysis of the latest (848 days) Super-Kamiokande (SK) atmospheric neutrino data going beyond the one mass scale dominance (OMSD) approximation. We fix $Δ_{12} = Δ_{13}$ ($Δ_{LSND}$) in the range 0.5 - 2 eV$^2$ as allowed by the results from LSND and other accelerator and reactor experiments on neutrino oscillation and keep $Δ_{23}$ ($Δ_{ATM}$) and the three mixing angles as free parameters. In such a scenario, the oscillation probabilities for the accelerator and reactor neutrinos involve only two of the mixing angles $θ_{12}$ and $θ_{13}$ and one mass scale. But the atmospheric neutrino oscillation is in general governed by both mass scales and all the three mixing angles. The higher mass scale gives rise to $Δm^2$ independent average oscillations for atmospheric neutrinos and does not enter the $χ^2$ analysis as an independent parameter. The $Δ_{23}$ and the three mixing angles on the other hand appear as independent parameters in the $χ^2$ analysis and the best-fit values of these are determined from an analysis of a) the SK data, b) the SK and CHOOZ data. The allowed values of the mixing angles $θ_{12}$ and $θ_{13}$ from the above analysis are compared with the constraints from LSND and other accelerator and reactor experiments. Implications for future long baseline experiments are discussed.

hep-ph↗

arXiv2001

MSW mediated neutrino decay and the solar neutrino problem

We investigate the solar neutrino problem assuming simultaneous presence of MSW transitions in the sun and neutrino decay on the way from sun to earth. We do a global $χ^2$-analysis of the data on total rates in Cl, Ga and Superkamiokande (SK) experiments and the SK day-night spectrum data and determine the changes in the allowed region in the $\dm - \tan^2θ$ plane in presence of decay. We also discuss the implications for unstable neutrinos in the SNO experiment.

hep-ph↗

arXiv2000

Status of the neutrino decay solution to the solar neutrino problem

We re-examine the neutrino decay solution to the solar neutrino problem in the light of the SuperKamiokande (SK) data. For the decay solution the SK spectrum data by its own can provide a fit comparable to the fit obtained from the MSW solution. However when one combines the results from the total rates of the $^{37}{Cl}$ and $^{71}{Ga}$ experiments the fit becomes much poorer.

hep-ph↗

arXiv2000

Effect of flavor mixing on the time delay of massive supernova neutrinos

The neutrinos and antineutrinos of all the three flavors released from a galactic supernova will be detected in the water Cerenkov detectors. We show that even though the neutral current interaction is flavor blind, and hence neutrino flavor mixing cannot alter the total neutral current signal in the detector, it can have a non-trivial impact on the delay of massive neutrinos and alters the neutral current event rate as a function of time. We have suggested various variables of the neutral and charged current events that can be used to study this effect. In particular the ratio of charged to neutral current events can be used at early times while the ratio of the energy moments for the charged to the neutral current events can form useful diagnostic tools even at late times to study neutrino mass and mixing.

hep-ph↗

arXiv2000

Is neutrino decay really ruled out as a solution to the atmospheric neutrino problem from Super-Kamiokande data?

In this paper we do a detailed $χ^2$-analysis of the 848 days of Super-Kamiokande(SK) atmospheric neutrino data under the assumptions of $ν_μ- ν_τ$ oscillation and neutrino decay. For the latter we take the most general case of neutrinos with non-zero mixing and consider the possibilities of the unstable component in $ν_μ$ decaying to a state with which it mixes (scenario (a)) and to a sterile state with which it does not mix (scenario (b)). In the first case $Δm^2$ (mass squared difference between the two mass states which mix) has to be $>$ 0.1 $eV^2$ from constraints on $K$ decays while for the second case $Δm^2$ can be unconstrained. For case (a) $Δm^2$ does not enter the $χ^2$-analysis while in case (b) it enters the $χ^2$-analysis as an independent parameter. In scenario (a) there is \dm averaged oscillation in addition to decay and this gets ruled out at 100.0% C.L. by the latest SK data. Scenario (b) on the other hand gives a reasonably good fit to the data for \dm $\sim 0.001 ~eV^2$.

hep-ph↗

arXiv1999

Flavor mixing and time of flight delay of supernova neutrinos

The neutrinos from galactic supernovae can be detected by the Sudbury Neutrino Observatory and the Super-Kamiokande. The effect of neutrino mass can show up in the observed neutrino signal by (i) delay in the time of flight and (ii) distortion of the neutrino energy spectrum due to flavor mixing. We discuss a combination of the two effects for both charged and neutral current processes in the detectors for realistic three flavor scenarios and show that neutrino flavor mixing can lead to non-trivial changes in the event rate as a function of time.

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