Low-energy solar anti-neutrinos
  If neutrino conversions within the Sun result in partial polarization of initial solar neutrino fluxes, then a new opportunity arises to observe the anti-\nu_e's in future neutrino experiments in the low energy region (such as BOREXINO or HELLAZ) and thus to probe the Majorana nature of the neutrinos. The \nu_e -> anti-\nu_e conversions may take place for low energy solar neutrinos while being unobservable at the Kamiokande and Super-Kamiokande experiments. 
V.B. Semikoz, S. Pastor and J.W.F. Valle