Predictions of Mixed Non‐Gaussian Cosmological Density Fields for the Cosmic Microwave Background Radiation

Abstract

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)f1(δ) + αf2(δ), where f1(δ) is a Gaussian distribution, f2(δ) is a non-Gaussian general distribution, and α is a scale-dependent mixture parameter. Results from simulations of CMBR temperature and polarization 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 as their predictions, and suggestions on how to apply them to small-scale CMBR observations. A reduced χ2 test shows that the contribution of an isocurvature fluctuation field is not ruled out in actual CMBR observations, even in the Wilkinson Microwave Anisotropy Probe first-year sky map.