  Using the records of the fluxes of solar neutrinos from the Homestake, GALLEX
(GNO), and Super-Kamiokande experiments, their statistical analyses were
performed to search for whether there existed a time variation of these fluxes.
The results of the analysis for the three experiments indicate that these
fluxes are varying quasi-biennially. This means that both efficiencies of the
initial p-p and the pp-III reactions of the proton-proton chain are varying
quasi-biennially together with a period of about 26 months. Since this time
variation prospectively generated by these two reactions strongly suggests that
the efficiency of the proton-proton chain as the main energy source of the Sun
has a tendency to vary quasi-biennially due to some chaotic or non-linear
process taking place inside the gravitationally stabilized solar fusion
reactor. It should be, however, remarked that, at the present moment, we have
no theoretical reasoning to resolve this mysterious result generally referred
to as the quasi-biennial periodicity in the time variation of the fluxes of
solar neutrinos. There is an urgent need to search for the reason why such a
quasi-biennial periodicity is caused through some physical process as related
to nuclear fusion deep inside the Sun.
