Does the LMA MSW solar solution imply the Dirac nature of neutrinos?
  Operating with the bilarge neutrino mixing, we show that in the option of Dirac neutrinos the fermion universality -- expressed by the proportionality of neutrino masses to charged-lepton masses -- predicts $\Delta m_{21}^2$ of the order $10^{-5} {\rm eV}^2$, consistently with the LMA MSW solar solution. In contrast, in the option of Majorana neutrinos the fermion universality -- introduced as the seesaw proportionality of neutrino masses to charged-lepton masses squared -- predicts $\Delta m_{21}^2$ of the order $10^{-8} {\rm eV}^2$, what is consistent rather with the LOW MSW solar solution. Thus, the favored LMA MSW estimation of $\Delta m_{21}^2$ might be a signal from the Dirac nature of neutrinos. 
Wojciech Krolikowski