Cosmological Consequences of Topological Defects: Dark Energy and Varying Fundamental Constants

TL;DR

This paper explores the cosmological implications of topological defects like domain walls, strings, and monopoles, examining their potential roles in dark energy, varying fundamental constants, and the constraints imposed by physical principles.

Contribution

It introduces a class of ideal models for domain wall networks, analyzes their stability and evolution, and investigates the effects of topological defects on fundamental constants within cosmological contexts.

Findings

Domain wall networks tend toward scaling behavior.

Realistic phase transitions are unlikely to produce stable lattice structures.

Constraints from the Equivalence Principle limit variations of the fine-structure constant.

Abstract

We investigated domain wall networks as a possible candidate to explain the present accelerated expansion of the universe. We discuss various requirements that any stable lattice of frustrated walls must obey and propose a class of `ideal' model (in terms of its potential to lead to network frustration). By using the results of the largest and most accurate three-dimensional field theory simulations of domain wall networks with junctions, we find compelling evidence for a gradual approach to scaling. We conjecture that, even though one can build (by hand) lattices that would be stable, no such lattices will ever come out of realistic domain wall forming cosmological phase transitions. We consider cosmic strings and magnetic monopoles in Bekenstein-type models and show that there is a class of models of this type for which the classical Nielsen-Olesen vortex and 't Hooft-Polyakov monopoles are still valid solutions. We show that Equivalence Principle constraints impose tight limits on the allowed variations of $\alpha$ induced by string networks on cosmological scales. We show that the results obtained using the spherical infall model for an infinite wavelength inhomogeneity are inconsistent with the results of a local linearized gravity study and we argue in favor of the second approach. We also criticize the claim that the value of $\alpha$ inside collapsed regions could be significantly different from the background one on the basis of these findings.