Helioseismology can test the Maxwell-Boltzmann distribution
  Nuclear reactions in stars occur between nuclei in the high-energy tail of the energy distribution and are sensitive to possible deviations from the standard equilibrium thermal-energy distribution. We are able to derive strong constraints on such deviations by using the detailed helioseismic information of the solar structure. If a small deviation is parameterized with a factor exp{-delta*(E/kT)^2}, we find that delta should lie between -0.005 and +0.002. However, even values of delta as small as 0.003 would still give important effects on the neutrino fluxes. 
S. Degl'Innocenti, G. Fiorentini, M. Lissia, P. Quarati, B. Ricci