  We consider a class of models involving interactions between ultra-light
scalar dark matter and Standard Model neutrinos. Such couplings modify the
neutrino mass splittings and mixing angles to include additional components
that vary in time periodically with a frequency and amplitude set by the mass
and energy density of the dark matter. Null results from recent searches for
anomalous periodicities in the solar neutrino flux strongly constrain the dark
matter-neutrino coupling to be orders of magnitude below current and projected
limits derived from observations of the cosmic microwave background.
