Addendum to: Solar neutrino oscillation parameters after first KamLAND results

In a previous paper [1], we presented a three-flavour oscillation analysis of the solar neutrino measurements and of the first data from the KamLAND experiment, in terms of the relevant mass-mixing parameters (delta m^2, theta_12, theta_13). The analysis, performed by including the terrestrial neutrino constraints coming from the CHOOZ (reactor), KEK-to-Kamioka (K2K, accelerator) and Super-Kamiokande (SK, atmospheric) experiments, provided a stringent upper limit on theta_13, namely, sin^2(theta_13)<0.05 at 3 sigma. We reexamine such upper bound in the light of a recent (although preliminary) reanalysis of atmospheric neutrino data performed by the SK collaboration, which seems to shift the preferred value of the largest neutrino square mass difference Delta m^2 downwards. By taking the results of the SK official reanalysis at face value, and by repeating the analysis in [1] with such a new input, we find that the upper bound on theta_{13} is somewhat relaxed: sin^2(theta_13)<0.067 at 3 sigma. Related phenomenological issues are briefly discussed

Solar Neutrinos (with a tribute to John. N. Bahcall)

John N. Bahcall championed solar neutrino physics for many years. Thanks to his pioneering and long-lasting contributions, this field of research has not only reached maturity, but has also opened a new window on physics beyond the standard electroweak model through the phenomenon of neutrino flavor oscillations. We briefly outline some recent accomplishments in the field, and also discuss a couple of issues that do not seem to fit in the ``standard picture,'' namely, the chemical controversy at the solar surface, and possible implications of recent gallium radioactive source experiments

Neutrino mass and mixing parameters: A short review

We present a brief review of the current status of neutrino mass and mixing parameters, based on a comprehensive phenomenological analysis of neutrino oscillation and non-oscillation searches, within the standard three-neutrino mixing framework

Neutrino Oscillations: A Global Analysis

We review the status of the neutrino oscillation physics (as of June 2003), with a particular emphasis on the present knowledge of the neutrino mass-mixing parameters in a three generation approach. We consider first the nu_mu-->nu_tau flavor transitions of atmospheric neutrinos. It is found that standard oscillations provide the best description of the SK+K2K data, and that the associated mass-mixing parameters are determined at 1 sigma (and dof=1) as: Delta m^2=(2.6 +-0.4) x 10^-3 eV^2 and sin^2(2theta)=1.00+0.00-0.05. Such indications, presently dominated by SK, could be strengthened by further K2K data. Then we analyze the energy spectrum of reactor neutrino events recently observed at KamLAND and combine them with solar and terrestrial neutrino data. We find that the solution to the solar neutrino problem at large mixing angle (LMA) is basically split into two sub-regions, that we denote as LMA-I and LMA-II. The LMA-I solution, characterized by lower values of the squared neutrino mass gap, is favored by the global data fit. Finally, we briefly illustrate how prospective data from the SNO and KamLAND can increase our confidence in the occurrence of standard matter effects in the Sun, which are starting to emerge from current data

Decays of supernova relic neutrinos

We propose that future observations of supernova relic neutrinos (SRN) can be used to probe neutrino decay models. We focus on invisible (e.g. Majoron) decays, and work out the general solution of SRN kinetic equations in the presence of oscillations plus decay. We then apply the general solution to specific decay scenario, and show that the predicted SRN event rate can span the whole range below the current experimental bounds. Therefore, future SRN observations will surely have an impact on the neutrino decay parameter space

Effects of matter density variations on dominant oscillations in long baseline neutrino experiments

Variations around the average density and composition of the Earth mantle may affect long-baseline (anti)neutrino oscillations through matter effects. For baselines not exceeding a few thousand km, such effects are known to be very small, and can be practically regarded as fractional contributions to the theoretical uncertainties. We perturbatively derive compact expressions to evaluate such contributions in phenomenologically interesting scenarios with three or four neutrinos and a dominant mass scale

Model-dependent and independent implications of the first Sudbury Neutrino Observatory results

We briefly discuss some implications of the first solar \nu results from the Sudbury Neutrino Observatory (SNO) experiment in the charged-current channel. We first show that the present SNO response function is very similar to the Super-Kamiokande (SK) one above 8.6 MeV in kinetic electron energy. On the basis of such equivalence we confirm, in a completely model-independent way, the SNO evidence for an active, non-electron neutrino component in the SK event sample, with a significance greater than 3 sigma. Then, by assuming no oscillations into sterile neutrinos, we combine the SK+SNO data to derive allowed regions for two free parameters: (i) the ratio f_B of the true B \nu flux from the Sun to the corresponding value predicted by the standard solar model (SSM), and (ii) the \nu_e survival probability <Pee>, averaged over the common SK and SNO response function. We obtain the separate 3sigma ranges: f_B=1.03^{+0.50}_{-0.58} (in agreement with the SSM central value, f_B=1) and <Pee> =0.34^{+0.61}_{-0.18} (in >3sigma disagreement with the standard electroweak model prediction, <Pee>=1, with strong anticorrelation between the two parameters. Finally, by taking f_B and its uncertainties as predicted by the SSM, we perform an updated analysis of the $2\nu$ active neutrino oscillation parameters (\delta m^2,\tan^2\omega) including all the solar \nu data, as well as the spectral data from the CHOOZ reactor experiment. We find that only the solutions at \tan^2\omega~O(1) survive at the 3sigma level in the global fit, with a preference for the one at high \delta m^2---the so-called large mixing angle solution

A phenomenological outlook on three-flavor atmospheric neutrino oscillations

The recent observations of atmospheric nu events from the Super-Kamiokande experiment are compatible with three-flavor neutrino oscillations, occurring dominantly in the nu_mu<--->nu_tau channel and subdominantly in the nu_mu<--->nu_e channel. We present an updated analysis of the three-flavor mass-mixing parameters consistent with the present phenomenology, including the latest 45 kTy data sample from Super-Kamiokande. A comparison with our previous results, based on 33 kTy data, shows that the oscillation evidence is strengthened, and that the neutrino mass-mixing parameters are constrained in smaller ranges

Indications on neutrino oscillations parameters from initial K2K and current SK data

We briefly discuss the impact of initial data from the KEK-to-Kamioka (K2K) neutrino experiment on the nu_mu-->nu_tau oscillation parameters (m^2,tan^2 psi) currently indicated by the Super-Kamiokande (SK) atmospheric neutrino experiment. After showing the very good agreement between K2K and SK, we combine the two separate pieces of information. We find that the 99% C.L. range for m^2 allowed by SK only, m^2=[1.3, 5.6]x10^-3 eV^2, is reduced to [1.5, 4.8]x10^-3 eV^2 by including K2K data. By halving the uncertainties of the K2K total rate (with central value unchanged), the m^2 range would be ulteriorly reduced to [1.8, 4.0]x10^-3 eV^2. Such information appears to be already useful in planning (very) long baseline neutrino oscillation experiments

Earth regeneration effect in solar neutrino oscillations: an analytic approach

We present a simple and accurate method for computing analytically the regeneration probability of solar neutrinos in the Earth. We apply this method to the calculation of several solar model independent quantities than can be measured by the SuperKamiokande and Sudbury Neutrino Observatory experiments