Nuclear aspects of the solar neutrino problem

The present status of the nuclear reaction rates determining the solar neutrino flux is discussed. This includes the reaction rates for the two branching ratios of the three pp-chains involving the reactions 3He(3He,2p)4He and 3He(4He,gamma)7Be for the first branching, and 7Be(e-,nu_e)7Li and 7Be(p,gamma)7B for the second branching. Mainly we will concentrate on the basic nuclear reaction p + p -> D + e+ + nu_e of the pp-chains. We use a relativistic field theory model of the deuteron to calculate the low-energy cross section for this reaction. The theoretical prediction of the cross section obtained is about 2.9 times largerthan given in the conventional potential approach. The consequences of this new reaction rate for the solar neutrino problem will be presented and discussed.