The Curvature Perturbation in the Axion-type Curvaton Model
  We study the axion-type curvaton model, with emphasis on the large field
regime where analytic results are very difficult to obtain. We evaluate the
tensor-scalar ratio $r$ using WMAP normalization and the non-linearity
parameters $f_{NL}$ and $g_{NL}$ by solving the equations numerically using the
$\delta N$ formalism. We compare them with results for the curvaton with
quadratic potential. We find that $r$ is much smaller for the axion-type case
compared to the result from the quadratic potential, with the difference
increasingly more pronounced at larger field values. $g_{NL}$ is found to be
positive, unlike the quadratic case where it is negative, and the amplitude of
$g_{NL}$ is much larger. Moreover, there is a nearly linear scaling between
$g_{NL}$ and $f_{NL}$, with small deviation from linearity at large field
values. The slope between $g_{NL}$ and $f_{NL}$ depends on the parameters
characterizing the axion-type curvaton model. We further consider a mixed
scenario where both the inflaton and the curvaton contribute to the primordial
power spectrum and the non-Gaussianity parameters are found to be much larger
than those in the case with quadratic potential.
