Electrically charged curvaton
  We consider the possibility that the primordial curvature perturbation was
generated through the curvaton mechanism from a scalar field with an electric
charge, or precisely the Standard Model U(1) weak hypercharge. This links the
dynamics of the very early universe concretely to the Standard Model of
particle physics, and because the coupling strength is known, it reduces the
number of free parameters in the curvaton model. The gauge coupling also
introduces several new physical effects. Charge fluctuations are generated
during inflation, but they are screened by electron-positron pairs therefore do
not violate observational constraints. After inflation, the curvaton interacts
with thermal radiation which destroys the curvaton condensate and prevents the
generation of curvature perturbations, unless the inflaton dynamics satisfy
strong constraints. The curvaton also experiences a period of parametric
resonance with the U(1) gauge field. Using the standard perturbative approach,
we find that the model can generate the observed density perturbation for
Hubble rate H_* > 10^8 GeV and curvaton mass m > 0.01 H_*, but with a level of
non-Gaussianity (f_NL > 130) that violates observational constraints. However,
previous studies have shown that the parametric resonance changes the predicted
perturbations significantly, and therefore fully non-linear numerical field
theory simulations are required.
