CMB Anomalies from Imperfect Dark Energy: Confrontation with the Data

TL;DR

This paper investigates anisotropic dark energy models by analyzing WMAP data, aiming to explain large-scale CMB anomalies through imperfect dark energy sources and their anisotropic effects.

Contribution

It introduces a parametrization of rotational invariance violations in dark energy and performs a comprehensive statistical analysis comparing models with observational data.

Findings

Preferred axis at (l,b) = (168°, -31°)

Anisotropy amplitude of approximately 0.51 with large uncertainty

Best-fit anisotropic spectrum is steep and blue with n_de ≈ 3.1

Abstract

We test anisotropic dark energy models with the 7-year WMAP temperature observations data. In the presence of imperfect sources, due to large-scale gradients or anisotropies in the dark energy field, the CMB sky will be distorted anisotropically on its way to us by the ISW effect. The signal covariance matrix then becomes nondiagonal for small multipoles, but at $\ell \gtrsim 20$ the anisotropy is negligible. We parametrize possible violations of rotational invariance in the late universe by the magnitude of a post-Friedmannian deviation from isotropy and its scale dependence. This allows to obtain hints on possible imperfect nature of dark energy and the large-angle anomalous features in the CMB. A robust statistical analysis, subjected to various tests and consistency checks, is performed to compare the predicted correlations with those obtained from the satellite-measured CMB full sky maps. The preferred axis point towards $(l,b) = (168^\circ, -31^\circ)$ and the amplitude of the anisotropy is $\varpi_0 = (0.51\pm 0.94)$ (1$\sigma$ deviation quoted). The best-fit model has a steep blue anisotropic spectrum ($n_{\mathrm{de}} = 3.1\pm1.5$).