Cosmic microwave background anomalies from imperfect dark energy

Abstract

We test anisotropic dark energy models with the 7-year WMAP temperature observation data. In the presence of imperfect sources, large-scale gradients or anisotropies in the dark energy mean that the CMB sky will be distorted anisotropically on its way to us by the ISW effect. The signal covariance matrix then becomes non-diagonal for small multipoles, but at > ∼ 20 the anisotropy is negligible for any reasonably probable values of the already constrained dark energy fluid parameters. As a consequence, only possible largescale anisotropies are studied in this paper. 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, where the deviation from isotropy is modeled through a mismatch between the φ and ψ potentials that arise due to anisotropic stresses caused by some (unknown) mechanism. In this sense, our model is general. In this paper we explore the possibility that the stresses are caused by an imperfect dark energy component in the form of a vector field aligned with some axis. This way we may obtain hints of the 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 points toward (l, b) = (168 • , −31 • ) and the amplitude of the anisotropy is 0 = (0.51 ± 0.94) (1σ deviation quoted). The best fit model has a steep blue anisotropic spectrum (n de = 3.1 ± 1.5). In light of recent studies, the model provides an interesting extension of the standard model of cosmology, since it is able to account for the apparent deficit in large-scale power in the spectrum through a physically motivated late time ISW effect. Further studies of this class of models are justified by the results of the analysis, which suggest that it cannot be ruled out at present.

Anisotropic cosmology and inflation from a tilted Bianchi IX model

“…From Eqs. (25) and (26) we furthermore see that = 1 in the curvature filled universe , = 3 in the shear filled universe ,…”

“…Its role differs from the shear and curvature anisotropies, as the vorticity decouples from the expansion. By this we mean that it does not enter the constraints (26,25) and thus does not act as an effective energy source for the expansion, but rather affects the dynamics of the overall scale factor indirectly via its dynamical impact on the evolution of the curvature and the shear. Furthermore, the redshift of a distant object is not directly dependent on V either, because it does not affect on the separation between two successive spatial hyper surfaces [47].…”

“…The equations to integrate are Eqs. (21)(22)(23)(24)(25)(26), but in order to describe full realistic cosmic history, we need include also dust and radiation…”

“…It is this oddness that appears the most unexpected and difficult to explain with the existing models. Proposed late-time origin for a parity violation include spontaneous isotropy breaking [24], imperfect dark energy field [25] and effects due to our peculiar velocity with respect to the CMB [26]. The primordial spectrum itself could contain dipole and other odd contributions only in the context of noncommutative theories [27], but parity-violating primordial modulations of the perturbations and thus of the resulting CMB temperature field might be generated by nontrivial multifield dynamics during inflation [28] or reheating [29], or by breaking translation invariance with isocurvature perturbations [30] or domain walls [31,32].The question we shall pursue here is whether our universe could be realistically described by a spacetime with slight anisotropies that distinguish orientation in way that would explain the parity-violating CMB anomalies.…”

“…We could of course write down the three dynamical equations(21,22,23,24) with the constraints(25,26) inserted explicitly but that would hardly give more insight to the properties of the system 4. The governing equations depend on λ only via cosh(2λ).…”