Predictions of mixed non - Gaussian cosmological density fields for the cosmic microwave background radiation

We present simulations of the Cosmic Microwave Background Radiation (CMBR) power spectrum for a class of mixed, non-Gaussian, primordial random fields. We assume a skew positive mixed model with adiabatic inflation perturbations plus additional isocurvature perturbations possibly produced by topological defects. The joint probability distribution used in this context is a weighted combination of Gaussian and non-Gaussian random fields, such as: P(δ) = (1-α)f 1 (δ) + αf 2 (δ), where f 1 (δ) is a Gaus-sian distribution, f 2 (δ) is a non-Gaussian general distribution, and α is a scale dependent mixture parameter. Results from simulations of CMBR temperature and polarisation power spectra show a distinct signature for very small deviations (< ∼ 0.1%) from a pure Gaussian field. We discuss the main properties of such mixed models as well, their predictions and suggestions on how to apply them to small scale CMBR observations. A reduced χ 2 test shows that the contribution of an isocurvature fluctuation field is not ruled out in actual CMB observations, even in WMAP first-year sky map.