Curvatons in supersymmetric models

We study the curvaton scenario in the supersymmetric framework, paying particular attention to the fact that scalar fields are inevitably complex in supersymmetric theories. If there is more than one scalar field associated with the curvaton mechanism, isocurvature (entropy) fluctuations between those fields in general arise, which may significantly affect the properties of the cosmic density fluctuations. We examine several candidates for the curvaton in the supersymmetric framework, such as moduli fields, the Affleck-Dine field, F- and D-flat directions, and the right-handed sneutrino. We estimate how the isocurvature fluctuations generated in each case affect the cosmic microwave background angular power spectrum. With the use of a recent observational result of the WMAP, stringent constraints on the models are derived and, in particular, it is seen that a large fraction of the parameter space is excluded if the Affleck-Dine field plays the role of the curvaton field. Natural and well-motivated candidates of the curvaton are also listed.