Random Matter Density Perturbations and LMA N. Reggiani Pontifícia Universidade Católica de Campinas - Campinas SP Brazil M. M. Guzzo and P. C. de Holanda Universidade Estadual de Campinas - Campinas SP Brazil Parallel session: Neutrino Properties and Oscillations

Energy spectrum observed in KamLAND Campatible with the predictions based on LMA realization of the MSW mechanism.  The best fit values of the relevant neutrino parameters which generate this solution   m 2 = 7.3 x eV 2 tan 2  = 0.41

Such an agreement of the LMA MSW predictions with the solar neutrino data is achieved assuming the standard approximately exponentially decaying solar matter distribution, which is in agreement with helioseismology observations. Also, when the MSW predictions are fittted to the solar neutrino data, it is assumed that the solar matter do not have any kind of perturbations. There are reasons to believe, nevertheless, that the solar matter density fluctuates around an equilibrium profile.

Possible reasons of density perturbations: 1. Temperature fluctuations due to convection of matter between layers with different temperatures; 2. Resonance between g-modes and magnetic Alfvén waves; 3. These g-modes can be excited by turbulent stresses in the convective zone;

Considering helioseismology, there are constrains on density fluctuations, but only those which vary over very long scales, much greater than 1000 km. The measured spectrum of helioseismic waves is largely insensitive to the existence of density variations whose wavelength is short enough to be of interest for neutrino oscillation - scales close to 100 km inside the solar core.

The survival probability of the neutrinos are obtained solving the evolution equation, considering the density profile perturbed by a random noise. The correlation length of this perturbation, L 0, must obey the following relations: l free << L 0 << m L free ==> mean free path of the electrons in the Sun m ==> characteristic neutrino oscillation This condition is satisfied if L 0 = 0.1 m, which implies 10 km < L 0 < 100 km in the resonant region for LMA effect.

Figure 1: Survival probability for two values of the mixing angle and for several values of perturbation amplitude:  = 0% (solid line),  = 2% (long dashed line),  = 4% (dashed line) and  = 8% (dotted line)

Figure 2: We observe that the values of  m 2 and sin 2 2  that satisfy both the solar neutrinos and KamLAND observations are shifted in the direction of lower values as the amplitude of the density noise increases. In the right-handed side, the combined analysis of both solar neutrino and KamLAND observations is shown.

Best fit values combining solar neutrino and KamLAND data.

Figure 3: (  2 -  2 min ) < 4 for 5% <  < 8%

Conclusion: random perturbation of the solar matter density will affect the determination of the best fit in the LMA region of the MSW mechanism. Taking into acount KamLAND results, the allowed regions of  m 2 and sin 2 2  moves from two distinct regions, the low-LMA and high-LMA, when no noise is assumed in the corresponding resonant region, to the VERY-low-LMA region, when a noise amplitude of 5% <  < 8% is assumed inside the Sun.