Curvaton and QCD axion in supersymmetric theories

A pseudo-Nambu-Goldstone boson as curvaton avoids the eta problem of inflation which plagues most curvaton candidates. We point out that a concrete realization of the curvaton mechanism with a pseudo-Nambu-Goldstone boson can be found in the supersymmetric Peccei-Quinn mechanism resolving the strong CP problem. In the flaton models of Peccei-Quinn symmetry breaking, the angular degree of freedom associated with the QCD axion can naturally be a flat direction during inflation and provides successful curvature perturbations. In this scheme, the preferred values of the axion scale and the Hubble parameter during inflation turn out to be about 10(10) and 10(12) GeV, respectively. Moreover, it is found that a significant isocurvature component, (anti)correlated to the overall curvature perturbation, can be generated, which is a smoking gun for the curvaton scenario. Finally, non-Gaussianity in the perturbation spectrum at a potentially observable level is also possible.