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Flavor-dependent long range (LR) leptonic forces, like those mediated by the $L_e-L_\mu$ or $L_e -L_\tau$ gauge bosons, constitute a minimal extension of the standard model that preserves its renormalizability. We study the impact of such interactions on the solar neutrino oscillations when the interaction range $R_{LR}$ is much larger than the Earth-Sun distance. The LR potential can dominate over the standard charged current potential inside the Sun in spite of strong constraints on the coupling $\alpha$ of the LR force coming from the atmospheric neutrino data and laboratory search for new forces. We demonstrate that the solar and atmospheric neutrino mass scales do not get trivially decoupled even if $\theta_{13}$ is vanishingly small. In addition, for $\alpha \gsim 10^{-52}$ and normal hierarchy, resonant enhancement of $\theta_{13}$ results in nontrivial energy dependent effects on the $\nu_e$ survival probability. We perform a complete three generation analysis, and obtain constraints on $\alpha$ through a global fit to the solar neutrino and KamLAND data. We get the $3\sigma$ limits $\alpha_{e\mu} < 3.4 \times 10^{-53}$ and $\alpha_{e\tau} < 2.5 \times 10^{-53}$ when $R_{LR}$ is much smaller than our distance from the galactic center. With larger $R_{LR}$, the collective LR potential due to all the electrons in the galaxy becomes significant and the constraints on $\alpha$ become stronger by upto two orders of magnitude., Comment: 25 pages, 7 figures

We explore a novel possibility of determining the solar model parameters, which serve as input in the calculations of the solar neutrino fluxes, by exploiting the data from direct measurements of the fluxes. More specifically, we use the rather precise value of the $^8B$ neutrino flux, $\phi_B$ obtained from the global analysis of the solar neutrino and KamLAND data, to derive constraints on each of the solar model parameters on which $\phi_B$ depends. We also use more precise values of $^7Be$ and $pp$ fluxes as can be obtained from future prospective data and discuss whether such measurements can help in reducing the uncertainties of one or more input parameters of the Standard Solar Model., Comment: 25 pages, 3 figures

We discuss the possibilities of high precision measurement of the solar neutrino mixing angle $\theta_\odot \equiv \theta_{12}$ in solar and reactor neutrino experiments. The improvements in the determination of $\sin^2\theta_{12}$, which can be achieved with the expected increase of statistics and reduction of systematic errors in the currently operating solar and KamLAND experiments, are summarised. The potential of LowNu $\nu-e$ elastic scattering experiment, designed to measure the $pp$ solar neutrino flux, for high precision determination of $\sin^2\theta_{12}$, is investigated in detail. The accuracy in the measurement of $\sin^2\theta_{12}$, which can be achieved in a reactor experiment with a baseline $L \sim (50-70)$ km, corresponding to a Survival Probability MINimum (SPMIN), is thoroughly studied. We include the effect of the uncertainty in the value of $\sin^2\theta_{13}$ in the analyses. A LowNu measurement of the $pp$ neutrino flux with a 1% error would allow to determine $\sin^2\theta_{12}$ with an error of 14% (17%) at 3$\sigma$ from a two-generation (three-generation) analysis. The same parameter $\sin^2\theta_{12}$ can be measured with an uncertainty of 2% (6%) at 1$\sigma$ (3$\sigma$) in a reactor experiment with $L \sim60 $ km, statistics of $\sim$60 GWkTy and systematic error of 2%. For the same statistics, the increase of the systematic error from 2% to 5% leads to an increase in the uncertainty in $\sin^2\theta_{12}$ from 6% to 9% at 3$\sigma$. The inclusion of the $\sin^2\theta_{13}$ uncertainty in the analysis changes the error on $\sin^2\theta_{12}$ to 3% (9%). The effect of $\sin^2\theta_{13}$ uncertainty on the $\sin^2\theta_{12}$ measurement in both types of experiments is considerably smaller than naively expected., Comment: Final version

We present the constraints on neutrino oscillation parameters $\Delta m^2_{\odot}$ and $\theta_{\odot}$ governing the solar neutrino oscillations from two generation analysis of solar and KamLAND data. We include the latest 766.3 ton year KamLAND data in our analysis. We also present the allowed values of parameters $\Delta m^2_{atm}$ and $\sin^2\theta_{atm}$ from two generation oscillation analysis of SuperKamiokande atmospheric and K2K data. For both cases we discuss the precision achieved in the present set of experiments and also how the precision can be improved in future. We also obtain the bounds on $\theta_{13}$ from three generation analysis of global oscillation data. We emphasise on the roles played by different data sets in constraining the allowed parameter ranges., Comment: Talk given by S. Goswami at 21st International Conference on Neutrino Physics and Astrophysics (Neutrino 2004), Paris, France, 14-19 Jun 2004

We investigate the impact of the 766.3 Ty KamLAND spectrum data on the determination of the solar neutrino oscillation parameters. We show that the observed spectrum distortion in the KamLAND experiment firmly establishes $\Delta m^2_{21}$ to lie in the low-LMA solution region. The high-LMA solution is excluded at more than 4$\sigma$ by the global solar neutrino and KamLAND spectrum data. The maximal solar neutrino mixing is ruled out at $6\sigma$ level. The $3\sigma$ allowed region in the $\Delta m^2_{21}-\sin^2\theta_{12}$ plane is found to be remarkably stable with respect to leaving out the data from one of the solar neutrino experiments from the global analysis. We perform a three flavor neutrino oscillation analysis of the global solar neutrino and KamLAND spectrum data as well. The $3\sigma$ upper limit on $\sin^2\theta_{13}$ is found to be $ \sin^2\theta_{13} <0.055$. We derive predictions for the CC to NC event rate ratio and day-night (D-N) asymmetry in the CC event rate, measured in the SNO experiment, and for the suppression of the event rate in the BOREXINO and LowNu experiments. Prospective high precision measurements of the solar neutrino oscillation parameters are also discussed., Comment: Additional backgrounds recently identified by the KamLAND collaboration included in the analysis. Fit of KamLAND data to neutrino oscillation seen to improve. Slight change in the best-fit value of $\Delta m^2$ obtained

In this paper we study the physics potential of the KamLAND detector in probing neutrino oscillation parameters through observation of supernova neutrinos. In particular, we discuss the possibilities of probing the mixing angle $\theta_{13}$ and determining the sign of $\Delta m^2_{32}$ from the total charged current(CC) event rates on the proton and $^{12}{C}$ target, as well as from the CC spectra. We discuss the chances of probing the earth matter effect induced modulations from the observation of CC spectra in the different CC reactions in KamLAND and find the volume required to get a statistically significant signature of the earth matter effect in different energy bins. We also calculate the event rates expected in the neutral current (NC) reactions on Carbon and free proton and investigate if the charged current to neutral current ratios, which are free of the absolute luminosity uncertainty in the supernova neutrino fluxes, can be useful in probing the oscillation parameters., Comment: 24 pages, 10 figures

We explore the impact of the data from the KamLAND experiment in constraining neutrino mass and mixing angles involved in solar neutrino oscillations. In particular we discuss the precision with which we can determine the the mass squared difference $\Delta m^2_{solar}$ and the mixing angle $\theta_{solar}$ from combined solar and KamLAND data. We show that the precision with which $\Delta m^_{solar}$ can be determined improves drastically with the KamLAND data but the sensitivity of KamLAND to the mixing angle is not as good. We study the effect of enhanced statistics in KamLAND as well as reduced systematics in improving the precision. We also show the effect of the SNO salt data in improving the precision. Finally we discuss how a dedicated reactor experiment with a baseline of 70 km can improve the $\theta_{solar}$ sensitivity by a large amount., Comment: Talk given at 4th International Conference on Nonaccelerator New Physics (NANP 03), Dubna, Russia, 23-28 Jun 2003

A new reactor power plant Shika-2, with a power of approximately 4 GW and at a distance of about 88 km from the KamLAND detector is scheduled to start operating in March 2006. We study the impact of the $\bar\nu_e$ flux from this reactor on the sensitivity of the KamLAND experiment to the solar neutrino oscillation parameters. We present results on prospective determination of $\Delta m^2_\odot$ and $\sin^2\theta_\odot$ using the combined data from KamLAND and the solar neutrino experiments, including the effect of the Shika-2 contribution to the KamLAND signal and the latest data from the salt enriched phase of the SNO experiment. We find that contrary to the expectations, the addition of the Shika-2 reactor flux does not improve the $\sin^2\theta_\odot$ sensitivity of KamLAND, while the ambiguity in $\Delta m^2_\odot$ measurement may even increase, as a result of the averaging effect between Kashiwazaki and the Shika-2 reactor contributions to the KamLAND signal., Comment: Version to appear in Phys. Lett. B

The physics implications of the just published salt phase data from the SNO experiment are examined. The effect of these data on the allowed ranges of the solar neutrino oscillation parameters, $\Delta_m^2_{21}$ and $\sin^2\theta_{12}$, are studied in the cases of two- and three- neutrino mixing. In the latter case we derive an upper limit on the angle $\theta_{13}$. Constraints on the solar $\nu_e$ transitions into a mixture of active and sterile neutrinos are also presented. Finally, we give predictions for the day-night asymmetry in the SNO experiment, for the event rate in the BOREXINO and LowNu experiments, and discuss briefly the constraints on the solar neutrino oscillation parameters which can be obtained with prospective KamLAND data., Comment: Version to appear in PLB

However the allowed range of $\theta_{\odot}$ ($\theta_{12}$) 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 $\theta_{\odot}$ 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 $\theta_{12}$ 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 $\theta_{12}$ sensitivity is concerned, particularly near maximal mixing. Among solar neutrino experiments we identify SNO as the most promising candidate for constraining $\theta_{12}$ 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 $\theta_{12}$ 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 $\tan^2\theta_{12}$ to within 14%. We also discuss the future Borexino and LowNu experiments., Comment: Treatment of KamLAND systematics includes the most optimistic estimates. Final conclusion unchanged. Version to appear in PRD

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 $\Delta m^2-\tan^2\theta$ plane. The best-fit from a combined analysis which uses the KamLAND rate plus global solar data comes at $\Delta m^2 = 6.06 \times 10^{-5}$ eV $^2$ and $\tan^2\theta=0.42$, 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 $\Delta m^2 = 7.15 \times 10^{-5}$ eV $^2$ and $\tan^2\theta=0.42$ 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 $3\sigma$. The LOW solution is now ruled out at about 5$\sigma$ w.r.t. the LMA solution., Comment: Version to appear in PLB

We investigate the potential of 3 kiloTon-years(kTy) of KamLAND data to further constrain the $\Delta m^2$ and $\tan^2\theta$ values compared to those presently allowed by existing KamLAND and global solar data. We study the extent, dependence and characteristics of this sensitivity in and around the two parts of the LMA region that are currently allowed. Our analysis with 3 kTy simulated spectra shows that KamLAND spectrum data by itself can constrain $\Delta m^2$ with high precision. Combining the spectrum with global solar data further tightens the constraints on allowed values of $\tan^2\theta$ and $\Delta m^2$. We also study the effects of future neutral current data with a total error of 7% from the Sudbury Neutrino Observatory. We find that these future measurements offer the potential of considerable precision in determining the oscillation parameters (specially the mass parameter)., Comment: 16 pages, to appear in J Phys. G

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 $\nu_e$ 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 $1\sigma$. We perform global $\nu_e-\nu_{active}$ oscillation analyses of solar neutrino data including the recent SNO results. LMA emerges as a huge favorite while LOW appears at the $3\sigma$ level. All the other solutions are disfavored at $3\sigma$ while SMA is virtually ruled out. Maximal mixing is disfavored at $3\sigma$. 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., Comment: Talk given at Conference on Physics Beyond the Standard Model: Beyond the Desert 02, Oulu, Finland, 2-7 Jun 2002

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 $\nu_e$ survival probability more precisely than what was possible from the SK and SNO CC combination. We perform global $\nu_e-\nu_{active}$ 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 $3\sigma$ level., Comment: Latest data included, minor clarifications and a reference added; final version to appear in PLB

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 $\chi^2$-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 $\Delta m^2-\tan^2\theta$ plane for different allowed values of $\alpha$ and examine how these areas change with the inclusion of decay. We obtain bounds on the decay constant $\alpha$ in this region which implies a rest frame life time $\tau_0/m_{2} > 8.7 \times 10^{-5}$ 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 $\alpha$ which could still be allowed., Comment: 15 pages, LaTex. Updated with the full SNO day-night spectrum data

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 $5 - 10 \sigma$ signal for $\nu_e$ 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 $\nu_e$ 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., Comment: Brief discussion on the first NC result from SNO added; final version to be published in the MPLA

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 $\Delta m^2_{21}$ and $\Delta m^2_{31} \approx \Delta m^2_{32}$ are taken to be in the solar and atmospheric ranges respectively. We incorporate the constraints on $\Delta$m$^2_{31}$ as obtained by the SuperKamiokande atmospheric neutrino data and determine the allowed values of $\Delta m^2_{21}$, $\theta_{12}$ and $\theta_{13}$ 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 $\theta_{13}$. Since the allowed values of $\theta_{13}$ are constrained to very small values by the CHOOZ experiment there is no qualitative change over the two generation allowed regions in the $\Delta m^2_{21} - \tan^2 \theta_{12}$ plane. The best-fit comes in the LMA region and no allowed area is obtained in the SMA region at 3$\sigma$ level from combined solar and CHOOZ analysis., Comment: One reference added. Version to apprear in PRD

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 $\chi^2$ analysis of the solar neutrino data in the framework of two neutrino mixing. We consider both $\nu_e -\nu_{active}$ and $\nu_e -\nu_{sterile}$ 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 $\nu_e-\nu_{active}$ 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$\sigma$ level from the global analysis. For the $\nu_e -\nu_{sterile}$ 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., Comment: Revised version with the analysis repeated for the updated nue-d cross-sections. References added

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 $\chi^2$-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 $\dm - \tan^2\theta$ plane in presence of decay. We also discuss the implications for unstable neutrinos in the SNO experiment., Comment: Final version to appear in Phys. Rev. D