arXiv subjects

Srubabati Goswami

Publications and source records attributed to Srubabati Goswami.

At least 127 records · Page 7Linked to original sources

arXiv2003

Exploring the sensitivity of current and future experiments to $θ_{\odot}$

However the allowed range of $θ_{\odot}$ ($θ_{12}$) did not change much with the inclusion of the KamLAND results. In this paper we probe if future data from KamLAND can increase the accuracy of the allowed range in $θ_{\odot}$ and conclude that even after 3 kton-year of statistics and most optimistic error estimates, KamLAND {\it may} find it hard to significantly improve the bounds on the mixing angle obtained from the solar neutrino data. We discuss the $θ_{12}$ sensitivity of the survival probabilities in matter (vacuum) as is relevant for the solar (KamLAND) experiments. We find that the presence of matter effects in the survival probabilities for $^8B$ neutrinos give the solar neutrino experiments SK and SNO an edge over KamLAND, as far as $θ_{12}$ sensitivity is concerned, particularly near maximal mixing. Among solar neutrino experiments we identify SNO as the most promising candidate for constraining $θ_{12}$ and make a projected sensitivity test for the mixing angle by reducing the error in the neutral current measurement at SNO. Finally we argue that the most accurate bounds on $θ_{12}$ can be achieved in a reactor experiment, if the corresponding baseline and energy can be tuned to a minimum in the survival probability. We propose a new reactor experiment which can give the value of $\tan^2θ_{12}$ to within 14%. We also discuss the future Borexino and LowNu experiments.

hep-ph↗

arXiv2003

Solar Neutrino Experiments: An Overview

This article describes the seven experiments Homestake, Kamiokande, SAGE, GALLEX, Super-Kamiokande, GNO and SNO which have so far provided data on the measurement of the solar neutrino fluxes. The detection mechanism, the salient features of the detectors and the results of each experiment are presented. How the solar neutrino problem has evolved and became more focused with each experimental data is summarized. The goals for the future experiments are outlined.

hep-ph↗

arXiv2003

The Solar Neutrino Problem after the first results from Kamland

The first results from the KamLAND experiment have provided confirmational evidence for the Large Mixing Angle (LMA) MSW solution to the solar neutrino problem. We do a global analysis of solar and the recently announced KamLAND data (both rate and spectrum) and investigate its effect on the allowed region in the $Δm^2-\tan^2θ$ plane. The best-fit from a combined analysis which uses the KamLAND rate plus global solar data comes at $Δm^2 = 6.06 \times 10^{-5}$ eV $^2$ and $\tan^2θ=0.42$, very close to the global solar best-fit, leaving a large allowed region within the global solar LMA contour. The inclusion of the KamLAND spectral data in the global fit gives a best-fit $Δm^2 = 7.15 \times 10^{-5}$ eV $^2$ and $\tan^2θ=0.42$ and constrains the allowed areas within LMA, leaving essentially two allowed zones. Maximal mixing though allowed by the KamLAND data alone is disfavored by the global solar data and remains disallowed at about $3σ$. The LOW solution is now ruled out at about 5$σ$ w.r.t. the LMA solution.

hep-ph↗

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.

hep-ph↗

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

Power law enhancement of neutrino mixing angles in extra dimensions

We study the renormalization of the $llHH$-type Majorana neutrino mass operator in a scenario where there is a compactified extra dimension and the fields involved correspond to only the standard model particles and their Kaluza-Klein excitations. We observe that in a two flavour scenario, where one of the neutrinos is necessarily $ν_τ$, it is indeed possible to generate a large mixing at $\sim$ 100 GeV starting from a very small mixing near the ultra-violet cutoff $\sim$ 30 TeV. {\em En passant}, we also derive the Higgs mass upper and lower limits from perturbative unitarity and stability of the potential, respectively.

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.

hep-ph↗

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.

hep-ph↗

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.

hep-ph↗

arXiv2001

Neutrino Anomalies and Quasi-Dirac neutrinos

We discuss possibility of describing solar, atmospheric and LSND results with four neutrinos forming two quasi-degenerate pairs. The simplest versions of this 2+2 scheme with either $ν_e$ or $ν_μ$ mixing exclusively with sterile neutrino is disfavored by the SNO and atmospheric neutrino results respectively. A generalized scheme with sterile state participating in both the solar and atmospheric oscillations is still allowed. We show thasolar and atmospheric oscillations is still allowed. We show that the complex pattern of mixing needed for this purpose follows from a simple L_e+L_μ-L_τ-L_s symmetry. Specific form of L_e+L_μ-L_τ-L_s symmetric mass matrix is determined from experimental results. Two theoretical schemes which lead to this form and a proper breaking of L_e+L_μ-L_τ-L_s symmetry are discussed.

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 deposition due to neutrino pair annhilation near rotating neutron stars

General relativistic effects have been shown to increase the energy deposition rate due to the process $ν\barν \to e^{+}e^{-}$ in supernovae and neutron stars. In this paper we study the effect of inclusion of the rotation of the star in the general relativistic treatment. We show that inclusion of rotation results in a reduction in the heating rate as compared to the no rotation case.

astro-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.

hep-ph↗

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

Supernova Constraints on Neutrino Mass and Mixing

In this article I review the constraints on neutrino mass and mixing coming from type-II supernovae. The bounds obtained on these parameters from shock reheating, r-process nucleosynthesis and from SN1987A are discussed. Given the current constraints on neutrino mass and mixing the effect of oscillations of neutrinos from a nearby supernova explosion in future detectors will also be discussed.

hep-ph↗

arXiv2001

Solar Neutrino Rates, Spectrum, and its Moments : an MSW Analysis in the Light of Super-Kamiokande Results

We re-examine MSW solutions of the solar neutrino problem in a two flavor scenario taking (a) the results on total rates and the electron energy spectrum from the 1117-day SuperKamiokande (SK) data and (b) those on total rates from the Chlorine and Gallium experiments. We find that the SMA solution gives the best fit to the total rates data from the different experiments. One new feature of our analysis is the use of the moments of the SK electron spectrum in a $χ^2$ analysis. The best-fit to the moments is broadly in agreement with that obtained from a direct fit to the spectrum data and prefers a $Δm^2$ comparable to the SMA fit to the rates but the required mixing angle is larger. In the combined rate and spectrum analysis, apart from varying the normalization of the $^8$B flux as a free parameter and determining its best-fit value we also obtain the best-fit parameters when correlations between the rates and the spectrum data are included and the normalization of the $^8$B flux held fixed at its SSM value. We observe that the correlations between the rates and spectrum data are important and the goodness of fit worsens when these are included. In either case, the best-fit lies in the LMA region.

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↗