Detection of MeV scale neutrinos and the solar energy paradigm

The fundamental solar energy paradigm establishes that the energy in the Sun is due to a series of nuclear reactions which turn hydrogen into helium. In particular, for the Sun the fundamental reaction corresponds to p + p → d + e ⁺ + υ _e + 0.42 MeV. This is a very slow process which drives the evolution of the Sun over a timescale of 10⁹ years. Electron neutrinos produced in the core interact only weakly and travel almost undisturbed from the core to the surface. They are a unique probe to explore the interior of stars. Observations of solar neutrinos are discussed in the paper. The solar energy paradigm proposed in 1938 by H. Bethe has been measured in realtime by Borexino at 10% level in 2014. This observation allows to probe the solar stability over a 10⁵ years timescale. At present, solar neutrinos offer the opportunity to understand the new Solar Abundance Problem, that is our lack of knowledge of the chemical composition of the Sun. Therefore, improving solar neutrino measurements is of great interest for astrophysics. At the same time, a better determination of some astrophysical factors will reduce uncertainties on predictions to better identify a possible inadequate assumption in the solar model. (paper)