| Limits on Isocurvature Perturbations from Non-Gaussianity in WMAP Temperature Anisotropy (2008) | |||||||||
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| We study the effect of primordial isocurvature perturbations on non-Gaussian properties in CMB temperature anisotropies. We consider generic forms of the non-linearity of isocurvature perturbations which can be applied to a wide range of theoretical models. We derive analytical expressions of the bispectrum and the Minkowski Functionals for CMB temperature fluctuations to describe the non-Gaussianity from isocurvature perturbations. By comparing the signal-to-noise ratio of isocurvature bispectra against adiabatic ones, it is found that the isocurvature non-Gaussianity in the quadratic isocurvature model, where the isocurvature perturbation S can be written as a quadratic function of the Gaussian variable sigma, S=sigma^2-, reaches f_NL=30 even if we consider the current observational limit on the fraction of isocurvature perturbations contained in the amplitude of primordial power spectrum alpha. We actually give constraints on the isocurvature non-Gaussianity from Minkowski Functionals for WMAP 5-year data. We do not find a significant signal of the isocurvature non-Gaussianity. For the quadratic isocurvature model, we obtain a stringent upper limit on the isocurvature fraction alpha. Comment: 12 pages, 5 figures, references added | |||||||||
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