Curvaton as dark matter with secondary inflation
  We consider a novel cosmological scenario in which a curvaton is long-lived
and plays the role of cold dark matter (CDM) in the presence of a short,
secondary inflation. Non-trivial evolution of the large scale cosmological
perturbation in the curvaton scenario can affect the duration of the short term
inflation, resulting in the inhomogeneous end of inflation. Non-linear
parameters of the curvature perturbation are predicted to be fNL ~ 5/4 and gNL
~ 0. The curvaton abundance can be well diluted by the short-term inflation and
accordingly, it does not have to decay into the Standard Model particles. Then
the curvaton can account for the present CDM with the isocurvature perturbation
being sufficiently suppressed because both the adiabatic and CDM isocurvature
perturbations have the same origin. As an explicit example, we consider the
thermal inflation scenario and a string axion as a candidate for this
curvaton-dark matter. We further discuss possibilities to identify the
curvaton-dark matter with the QCD axion.
