The Sun: Light Dark Matter and Sterile Neutrinos
  Next-generation experiments allow for the possibility to testing the neutrino
flavor oscillation model to very high levels of accuracy. Here, we explore the
possibility that the dark matter in the current universe is made of two
particles, a sterile neutrino and a very light dark matter particle. By using a
3+1 neutrino flavor oscillation model, we study how such a type of dark matter
imprints the solar neutrino fluxes, spectra, and survival probabilities of
electron neutrinos. The current solar neutrino measurements allow us to define
an upper limit for the ratio of the mass of a light dark matter particle
$m_\phi$ and the Fermi constant $G_\phi$, such that $G_\phi/m_\phi $ must be
smaller than $10^{30}\; G_{\rm F}\; eV^{-1}$ to be in agreement with current
solar neutrino data from the Borexino, Sudbury Neutrino Observatory, and
Super-Kamiokande detectors. Moreover, for models with a very small Fermi
constant, the amplitude of the time variability must be lower than $3\%$ to be
consistent with current solar neutrino data. We also found that solar neutrino
detectors like Darwin, able to measure neutrino fluxes in the low energy-range
with high accuracy, will provide additional constraints to this class of models
that complement the ones obtained from the current solar neutrino detectors.
