Passive Curvaton
  We propose a class of curvaton models which we call passive curvaton. In this
paper, two kinds of passive curvaton is considered. The first one is a
pseudoscalar curvaton couples to a gauge field. Different from the inflaton
case, the constraint from formation of primordial black holes (PBHs) is much
weaker and large non-gaussianity (of the equiliteral type) can be produced. The
second model is a dilaton-like scalar curvaton couples to a gauge field. We
investigate the scale dependence of non-gaussianity in this model. In both
models, the spectrum and non-Gaussianity are enhanced by the slow-roll
parameter of the curvaton field. Other possible passive curvaton models are
also mentioned.
