It is noted that the theory of neutrino oscillations can be constructed only
in the framework of the particle physics theory, where is a mass shell
conception and then transitions (oscillations) between neutrinos with equal
masses are real and between neutrinos with different masses are virtual. It is
necessary to solve the question: which type of neutrino transitions
(oscillations) is realized in nature? There can be three types of neutrino
transitions (oscillations). At present it is considered that Dirac and Majorana
neutrino oscillations can be realized. It is shown that we cannot put Majorana
neutrinos in the standard weak interactions theory without violation of the
gauge invariance. Then it is obvious that there can be only realized
transitions (oscillations) between Dirac neutrinos with different flowers. Also
it is shown that the mechanism of resonance enhancement of neutrino
oscillations in matter cannot be realized without violation of the law of
energy-momentum conservation. Though it is supposed that we see neutrino
oscillations in experiments, indeed there only transitions between neutrinos
are registered. In order to register neutrino oscillations it is necessary to
see second or even higher neutrino oscillation modes in experiments. For this
purpose we can use the elliptic character of the Earth orbit. The analysis
shows that the SNO experimental results do not confirm smallest of nu_e to
nu_\tau transition angle mixings, which was obtained in CHOOZ experiment. It is
also noted that there is contradiction between SNO, Super-Kamiokande, Homestake
and the SAGE and GNO (GALLEX) data.Comment: LATEX, 20 pages, no figures and table