CMB constraint on non-Gaussianity in isocurvature perturbations

Abstract

We study the CMB constraints on non-Gaussianity in CDM isocurvature perturbations. Non-Gaussian isocurvature perturbations can be produced in various models at the very early stage of the Universe. Since the isocurvature perturbations little affect the structure formation at late times, CMB is the best probe of isocurvature non-Gaussianity at least in the near future. In this paper, we focus on non-Gaussian curvature and isocurvature perturbations of the local-type, which are uncorrelated and in the form, and constrain the non-linearity parameter of isocurvature perturbations, f (ISO) NL , as well as the curvature one f NL . For this purpose, we employ several state-of-art techniques for the analysis of CMB data and simulation. Assuming that isocurvature perturbations are subdominant, we apply our method to the WMAP 7-year data of temperature anisotropy and obtain constraints on a combination α 2 f (ISO) NL , where α is the ratio of the power spectrum of isocurvature perturbations to that of the adiabatic ones. When the adiabatic perturbations are assumed to be Gaussian, we obtained a constraint α 2 f (ISO) NL = 40 ± 66 assuming the power spectrum of isocurvature perturbations is scale-invariant. When we assume that the adiabatic perturbations can also be non-Gaussian, we obtain f NL = 38 ± 24 and α 2 f (ISO) NL = −8 ± 72. We also discuss implications of our results for the axion CDM isocurvature model.

Isocurvature constraints and anharmonic effects on QCD axion dark matter

“…The main results of this subsection are (17) and (21), which will be used later to calculate ∂N/∂a * .…”

“…Thus, taking both the initial flat slicing and final uniform density slicing to be in the matter-dominated era, the e-folding N between them depends on ρ c on the initial slicing as 16 The results in this page can also be derived from the following equation in the matter-dominated era:…”

Axion dark matter from topological defects

“…In particular, the cosmological scenario becomes different according to whether the PQ symmetry is broken after inflation or not. If the PQ symmetry is restored during inflation, the isocurvature perturbations induced by the quantum fluctuations of the axion field during inflation affect the observational results of the cosmic microwave background, putting a stringent constraint on the axion models if the inflationary scale is sufficiently high [10][11][12][13][14][15][16][17]. On the other hand, if the PQ symmetry is broken after inflation, topological defects such as strings and domain walls are formed, and we must take account of their evolution in the early universe.…”

Fermionic isocurvature perturbations

“…Although the isocurvature non-Gaussianities parameter f S N L should not be compared directly with f N L defined by the curvature perturbation [91], this can be done with the extra O(1) correction factor [31,34,74,[92][93][94]. The reason why ∂ 2 m n ψ appears instead of a first derivative is because of the squeezed triangle limit allows the short distance propagator to become important.…”