3He Transport and the Question of Nonstandard Solar Models

I consider phenomenological changes in the standard solar model with the goal of testing recent claims that the solar neutrino puzzle requires new particle physics. The assumption of a steady-state sun producing the correct luminosity and governed by standard microphysics appears to leave only one nonstandard solar model possibility open, slow mixing of the solar core on timescales characteristic of 3He equilibration. The conjecture of such mixing raises striking physics issues connected with the standard model 3He instability and the possibility that the 3He abundance gradient might allow the sun's early convective core to persist. While helioseismology might eventually rule out such a "model," contrary to one recent claim I will argue that the helioseismology of a mixed two-fluid sun is as yet far from clear. Finally, I conclude by stressing that 3He-driven slow mixing is not being proposed as a solution of the solar neutrino problem, but as an example of a possibility that has not been quantitatively modeled and yet could produce neutrino fluxes far closer to experiment than the standard solar model. Thus, despite the attractiveness of neutrino oscillation solutions, astrophysical explanations of the solar neutrino problem are not yet, in my view, ruled out definitively.