It is for these reasons that physicists are looking for modifications to the Standard Model of particle physics rather than to the theory of stars. The Standard Model is also brilliantly successful, yet many believe that its description of the neutrino is overly simplistic. It is assumed in the Standard Model that the neutrino has zero mass. It has been shown, however, that if the neutrino has a non-zero mass, then the solar neutrino problem could be solved. It should be noted that the idea of neutrinos with mass is not a new idea.
Many physicists also see massive neutrinos as part of the solution to the problem of dark matter.
The Sun produces only electron neutrinos, and this is the only type, or 'flavour' to which the solar neutrino experiments are sensitive. In the Standard Model, these three flavours are strictly conserved. The probability of metamorphosis varies sinusoidally with path length, and for this reason the effect is known as neutrino oscillation . This arises because of the different ways in which the different flavours of neutrinos interact with matter. The effect is usually referred as the 'MSW' effect.