The internal structure of the sun and the solar neutrinos problem

The observed neutrino flux (Davis experiment) is known to be too small by a factor 3 to 4 compared to the predicted flux. Here is given a review of the physical processes which determine the properties of the solar model: equation of state, absorption coefficient, nuclear cross-section, thermonuclear reaction rate, convection. Standard models give a solar neutrino flux around 7.6 S.N.U. (Solar neutrino Units=10-36 reaction atom-1 sec-1). Non-standard models are briefly discussed. Stellar rotation generates meridional circulation and differential rotation which themselves produce shear flow instabilities. This suggest the presence of a mild turbulence and mixing by turbulent diffusion. Astrophysical confirmation of turbulent diffusion mixing is given. Turbulent diffusion mixing can explain the neutrino deficiency by a change of chemical composition of the central regions of the sun. Solar sismology, surface abundance ratio and neutrino deficiency suggest a strongly radius-dependent coefficient of turbulent diffusion. The measure of the neutrino flux appeared then as one of the key of solar structure