Runnings in the Curvaton
  We investigate the scale-dependence, or the runnings, of linear and second
order density perturbations generated in various curvaton scenarios. We argue
that the second order perturbations, i.e. non-Gaussianity, can strongly depend
on the scale, even when the linear perturbations are nearly scale-invariant. We
present analytic formulae for the runnings from curvatons with general energy
potentials, and clarify the conditions under which fNL becomes strongly
scale-dependent. From the point of view of the fNL running, curvaton potentials
can be classified into roughly two categories by whether the potential flattens
or steepens compared to a quadratic one. As such examples, we study
pseudo-Nambu-Goldstone curvatons, and self-interacting curvatons, respectively.
The dynamics of non-quadratic curvatons and the behaviors of the resulting
density perturbations are clarified by analytical methods. Then we also study
models where multiple source can be responsible for density perturbations such
as the multi-curvaton, and mixed curvaton and inflaton models where the running
of fNL can also be large due to their multi-source nature. We make quantitative
analysis for each curvaton scenario and discuss in what cases the
scale-dependence, in particular, of fNL can be large enough to be probed with
future CMB experiments.
