Anisotropic Dark Energy: Dynamics of Background and Perturbations (0801.3676v2)

Abstract: We investigate cosmologies where the accelerated expansion of the Universe is driven by a field with an anisotropic equation of state. We model such scenarios within the Bianchi I framework, introducing two skewness parameters to quantify the deviation of pressure from isotropy. We study the dynamics of the background expansion in these models. A special case of anisotropic cosmological constant is analyzed in detail. The anisotropic expansion is then confronted with the redshift and angular distribution of the supernovae type Ia. In addition, we investigate the effects on the cosmic microwave background (CMB) anisotropies for which the main signature appears to be a quadrupole contribution. We find that the two skewness parameters can be very well constrained. Tightest bounds are imposed by the CMB quadrupole, but there are anisotropic models which avoid this bound completely. Within these bounds, the anisotropy can be beneficial as a potential explanation of various anomalous cosmological observations, especially in the CMB at the largest angles. We also consider the dynamics of linear perturbations in these models. The covariant approach is used to derive the general evolution equations for cosmological perturbations taking into account imperfect sources in an anisotropic background. The implications for the galaxy formation are then studied. These results might help to make contact between the observed anomalies in CMB and large scale structure and fundamental theories exhibiting Lorentz violation.

Anisotropic Dark Energy: Dynamics of Background and Perturbations

In "Anisotropic Dark Energy: Dynamics of Background and Perturbations," Koivisto and Mota explore the intriguing possibility that the accelerated expansion of the Universe is influenced by an anisotropic field. This paper diverges from the classical assumption of isotropic dark energy, proposing instead a framework wherein the equation of state exhibits directional dependence within the Bianchi I cosmology model. Through meticulous analysis, this paper explores both the theoretical underpinnings and observational implications of an anisotropic cosmological paradigm.

The authors introduce skewness parameters that quantify the deviations of pressure from isotropy, accounting for potential anisotropies in the universe's expansion dynamics. The paper rigorously analyzes a special case of anisotropic cosmological constant, addressing its compatibility with empirical observations such as supernovae type Ia redshift distributions and cosmic microwave background (CMB) anisotropies. The presence of these skewness parameters in perturbative models suggests that any profound deviation from isotropy can be effectively constrained—especially when considering the strong bounds imposed by CMB quadrupole measurements.

Numerically, while the influence of skewness parameters leads to anisotropic expansion models, it opens avenues for explaining various cosmological anomalies, particularly in CMB's grand angular scales. The proposed framework offers potential insight into perturbations dynamics, facilitated through the covariant approach, to evaluate linear perturbations evolution while factoring imperfect sources in the anisotropic background. This might further elucidate galaxy formation processes, potentially bridging observed anomalies in large-scale cosmic structures with Lorentz violating theoretical constructs.

In the broader spectrum, the paper challenges the longstanding cosmological constant paradigm, inviting speculation on alternative dark energy models exhibiting direction-dependence. This investigation may have significant ramifications for understanding cosmological inflation models where early universe anisotropies seeded the statistical anisotropies observed today.

The implications of this research extend from theoretical fronts to practical observations, questioning our foundational cosmological assumptions. Ultimately, it beckons further exploration into how anisotropic stresses interact with the universe's evolving space-time fabric, considering ongoing advancements in AI-assisted analytical methods for cosmic data interpretation. Speculating beyond fixed cosmological parameters suggests a tantalizing frontier in the comprehension of the universe's profound structures.