Thermal distributions in stellar plasmas, nuclear reactions and solar neutrinos, Brazilian

The physics of nuclear reactions in stellar plasma is reviewed with special emphasis on the impor-tance of the velocity distribution of ions. Then the properties (density and temperature) of the weak-coupled solar plasma are analysed, showing that the ion velocities should deviate from the Maxwellian distribution and could be better described by a weakly-nonexstensive (jq 1j < 0:02) Tsallis ' distribution. We discuss concrete physical frameworks for calculating this deviation: the in-troduction of higher-order corrections to the diusion and friction coecients in the Fokker-Planck equation, the in uence of the electric-microeld stochastic distribution on the particle dynamics, a velocity correlation function with long-time memory arising from the coupling of the collective and individual degrees of freedom. Finally, we study the eects of such deviations on stellar nu-clear rates, on the solar neutrino uxes, and on the pp neutrino energy spectrum, and analyse the consequences for the solar neutrino problem.