We discuss multi-field models of inflation, such as the curvaton, modulated reheating scenario, as the origin of density fluctuations. After summarizing the current status of such models from the viewpoint of observations of the scalar spectral index, the tensor-to-scalar ratio and so on, we investigate the CMB spectral μ. distortion in such a model, which captures the property of density fluctuations on small scales. We find that, given the current constraint on the spectral index and the tensor-to-scalar ratio, the predicted distribution of the value of μ in multi-field models could be broader than that in the standard single-field inflation model and larger values of μ could be realized. Some issues of isocurvature fluctuations in multi-field models are also discussed.
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