Solar photons, phonons and neutrinos

The inside of the Sun is not directly accessible to observations. Nonetheless, it is possible to construct a reasonable picture of its interior with the help of the theory of stellar structure along with the input physics describing a multitude of processes occurring inside the Sun. In order to check the validity of these theoretical models there have been valiant attempts to measure the Aux of neutrinos generated in the Sun's energy-generating core. The solar neutrino event rates reported by all the experiments to date have been consistently lower than those predicted by standard solar models. There is now a complementary probe, furnished by the accurately measured helioseismic data which provides stringent constraints on the physical conditions prevailing inside the Sun. It turns out that the helioseismically inferred density and sound speed profiles throughout the Sun's internal layers are close to those obtained with a standard solar model. A cooler solar core is, therefore, not a viable solution to account for the deficit in the measured neutrino fluxes. This leads one to the unavoidable conclusion that the solution to the solar neutrino puzzle should be sought in the realm of particle physics. (C) 1998 Elsevier Science Ltd. All rights reserved.