Effect of Coulomb collisions on time variations of the solar neutrino flux

We consider the processes that might suppress the time variations in the solar neutrino flux produced by the radial motion of the Earth through the neutrino interference pattern. We calculate these time variations and the extent to which they are suppressed by Coulomb collisions of the neutrino-emitting nuclei. This is done for both the 0.862-MeV Be-7 neutrino line and the continuous neutrino spectrum, assuming a Gaussian energy response function of the neutrino detector. We find that the collisional decoherence averages out the time variations for neutrino masses m(2)(2) - m(1)(2) greater than or similar to 10(-7) eV(2) epsilon(MeV)(3/2). A simple and clear physical picture of the time-dependent solar neutrino problem is presented and qualitative coherence criteria are discussed.