E6leptoquarks and the solar-neutrino problem

The possibility that nonconventional neutrino oscillations take place in the superstring-inspired ${\mathrm{E}}_6$ models is considered. In this context, the influence of leptoquark-mediated interactions of the neutrinos with nucleons in the resonant flavor conversion is discussed. It is shown that this effect can be significant for ${\nu }_e-{\nu }_{\tau }$ oscillations if these neutrinos have the masses required in the ordinary Mikheyev-Smirnov-Wolfenstein effect, and may lead to a solution of the solar-neutrino problem even in the absence of vacuum mixings. On the other hand, this model cannot lead to resonant behavior in the Sun if the neutrinos are massless.