  We consider the possibility of time variations of the solar neutrino flux due
to the radial motion of the Earth and neutrino interference effects. We
calculate the time variations of the detected neutrino flux and the extent to
which they are suppressed by Coulomb collisions of the neutrino emitting
nuclei. To properly treat the collisions, it is necessary to simultaneously
include in our analysis all other significant physical decoherence effects: the
energy averaging and the averaging over the position of neutrino emission.
  A simple and clear physical picture of the time dependent solar neutrino
problem is presented and qualitative coherence criteria are discussed. Exact
results for the detected neutrino flux and its time variations are obtained for
both the case of a solar neutrino line, and the case of the continuous neutrino
spectrum with a Gaussian shape of the energy response function of the neutrino
detector. We give accurate constraints on the vacuum mixing angle and the
neutrino masses required for flux time variations to not be suppressed.
  Pac(s): 26.65.+t, 14.60.Pq, 96.60.Jw
