Theoretical Implications of the Combined Solar Neutrino Observations
  Constraints on the core temperature of the Sun and on neutrino-oscillation parameters are obtained by comparing the combined Homestake, Kamiokande, SAGE and GALLEX solar neutrino data with Standard Solar Models (SSM) and with non-standard solar models parameterized by a phenomenological central temperature ($T_c$). If the Sun is 2\% cooler or 3\% warmer than predicted by SSMs, the MSW parameters we determine are consistent with different grand unified theories. 
S.A. Bludman, N. Hata, D.C. Kennedy, P.G. Langacker