Modelling the emergence of cosmic anisotropy from non-linear structures

TL;DR

This paper introduces a novel cosmological modeling approach where large-scale anisotropy naturally emerges from the growth of non-linear structures, using field decomposition and averaging techniques.

Contribution

It develops a new method to derive effective field equations for emergent anisotropy from non-linear structure growth, connecting to Bianchi cosmologies.

Findings

Effective large-scale anisotropy equations derived

Application to Farnsworth solutions demonstrates anisotropic expansion

Framework links non-linear structure growth to cosmic anisotropy

Abstract

Astronomical observations suggest that the Universe may be anisotropic on the largest scales. In order to model this situation, we develop a new approach to cosmology that allows for large-scale anisotropy to emerge from the growth of non-linear structure. This is achieved by decomposing all relevant fields with respect to a preferred space-like direction, and then averaging the resulting scalar quantities over spatial domains. Our approach allows us to derive a set of large-scale effective field equations that govern the dynamics of any emergent large-scale anisotropy, and which (up to back-reaction terms) take the form of the field equations of the locally rotationally symmetric Bianchi cosmologies. We apply our approach to the dust-filled Farnsworth solutions, which are an interesting set of exact cosmological models that allow for both anisotropic expansion and large-scale bulk flow.