Metal abundance in the solar interior

It is shown that the metal abundance in the solar interior is constrained by the current solar neutrino experiments under the assumption of neutrino conversion in the Sun due to neutrino oscillation via the Mikhyev-Smirnov-Wolfenstein (MSW) effect, the most widely accepted solution to the solar neutrino problem. The metal abundance strongly affects the CNO neutrino flux, and an excessive increase of the CNO flux is incompatible with the region allowed by the solar neutrino experiments in neutrino-oscillation parameter space. The result shows that the metal abundance in the interior should be within the range 0.5-1.4 times that in the surface, supporting the idea that the Sun formed by a contraction of a gas cloud with an almost homogeneous composition.