Neutrino Non-Standard Interactions via Light Scalars in the Earth, Sun,
  Supernovae and the Early Universe
  Non-standard interactions (NSI) of neutrinos with matter mediated by a scalar
field would induce medium-dependent neutrino masses which can modify
oscillation probabilities. Generating observable effects requires an
ultra-light scalar mediator. We derive general expressions for the scalar NSI
using techniques of quantum field theory at finite density and temperature,
including the long-range force effects, and discuss various limiting cases
applicable to the neutrino propagation in different media, such as the Earth,
Sun, supernovae and early Universe. We also analyze various terrestrial and
space-based experimental constraints, as well as astrophysical and cosmological
constraints on these NSI parameters, applicable to either Dirac or Majorana
neutrinos. By combining all these constraints, we show that observable scalar
NSI effects, although precluded in terrestrial experiments, are still possible
in future solar and supernovae neutrino data, and in cosmological observations
such as cosmic microwave background and big bang nucleosynthesis data.
