Linear Growth of Structure in the Symmetron Model

TL;DR

This paper investigates the linear growth of cosmic structures within the symmetron model, revealing that the symmetron's fifth force influences structure formation with minimal impact from brief tachyonic instabilities.

Contribution

It provides analytic solutions and numerical analysis of the symmetron model's effects on large-scale structure growth, highlighting the limited impact of tachyonic instability.

Findings

Tachyonic instability has negligible effects on sub-horizon structure growth.

Symmetron fifth force affects structure formation in a nontrivial, potentially observable way.

Analytic solutions agree well with numerical results.

Abstract

In the symmetron mechanism, the fifth force mediated by a coupled scalar field (the symmetron) is suppressed in high-density regions due to the restoration of symmetry in the symmetron potential. In this paper we study the background cosmology and large scale structure formation in the linear perturbation regime of the symmetron model. Analytic solutions to the symmetron in the cosmological background are found, which agree well with numerical results. We discuss the effect of the symmetron perturbation on the growth of matter perturbation, in particular the implications of the brief period of tachyonic instability caused by the negative mass squared of the symmetron during symmetry breaking. Our analysis and numerical results show that this instability has only very small effects on the growth of structures on sub-horizon scales, and even at horizon scales its influence is not as drastic as naively expected. The symmetron fifth force in the non-tachyonic regime does affect the formation of structure in a nontrivial way which could be cosmologically observable.