Pontecorvo neutrino-antineutrino oscillations: Theory and experimental limits

We study Pontecorvo neutrino-antineutrino oscillations both in vacuum and in matter within a field theoretic approach, showing that this phenomenon can occur only if neutrinos have a Dirac-Majorana mass term. We find that matter effects suppress these oscillations and cannot explain the solar neutrino problem. On the contrary, a vacuum neutrino-antineutrino oscillations solution to this problem exists. We analyze this solution and the available data from laboratory experiments giving stringent limits on nu(e) and nu(mu) Majorana masses.