ar X iv : h ep - p h / 03 03 20 3 v 1 2 4 M ar 2 00 3 Large mixing angle solution to the solar neutrino problem and random matter density perturbations

There are reasons to believe that mechanisms exist in the solar interior which lead to random density perturbations in the resonant region of the Large Mixing Angle solution to the solar neutrino problem. We find that, in the presence of these density perturbations, the best fit point in the (sin 2θ,∆m) parameter space moves to smaller values, compared with the values obtained for the standard LMA solution. Combining solar data with KamLAND results, we find a new compatibility region, which we call VERY-LOW LMA, where sin 2θ ≈ 0.6 and ∆m ≈ 2× 10 eV, for random density fluctuations of order 5% < ξ < 8%. We argue that such values of density fluctuations are still allowed by helioseismological observations at small scales of order 10 1000 km deep inside the solar core. Assuming CPT invariance, the electronic antineutrino ν̄e disappearance as well as the neutrino energy spectrum observed in KamLAND [1] are compatible with the predictions based on the Large Mixing Angle (LMA) realization of the MSW mechanism, resonantly enhanced oscillations in matter [2, 3]. This compatibility makes LMA the best solution to the solar neutrino anomaly [4][10]. The best fit values of the relevant neutrino parameters which generate such a solution are ∆m = 7.3 × 10 eV and tan θ = 0.41 with a free boron neutrino flux fB = 1.05 [11] with the 1 σ intervals: ∆m 2 = (6.2 ↔ 8.4)× 10 eV and tan θ = 0.33 ↔ 0.54.