We discuss microscopic cluster model descriptions of two solar nuclear
reactions, Be7(p,gamma)B8 and He3(He3,2p)He4. The low-energy reaction cross
section of Be7(p,gamma)B8, which determines the high-energy solar neutrino
flux, is constrained by Be7 and B8 observables. Our results show that a small
value of the zero-energy cross section is rather unlikely. In He3(He3,2p)He4 we
study the effects of a possible virtual state on the cross section. Although,
we have found no indication for such a state so far, its existence cannot be
ruled out yet. We calculate the He3(He3,2p)He4 and H3(H3,2n)He4 cross sections
in a continuum-discretized coupled channel approximation, and find a good
general agreement with the data.Comment: 9 pages with 4 figures. Invited talk given at the "XVII RCNP
International Symposium on Innovative Computational Methods in Nuclear
Many-Body Problems" (November 10-15, 1997, Osaka, Japan). To appear in the
conference proceedings. The postscript file with color figures and more
information are available at http://qmc.lanl.gov/~csot
