Linear perturbations in viable f(R) theories

TL;DR

This paper analyzes the linear perturbation evolution in three viable f(R) gravity models, highlighting their potential to be distinguished from Lambda-CDM through structure growth observations, despite observational challenges.

Contribution

It provides a detailed comparison of linear perturbations in three f(R) models and assesses their observational distinguishability from Lambda-CDM.

Findings

Linear perturbation growth differs slightly between models.

Future space experiments may detect differences up to 4%.

Relaxed local constraints increase model distinguishability.

Abstract

We describe the cosmological evolution predicted by three distinct $f(R)$ theories, with emphasis on the evolution of linear perturbations. The most promising observational tools for distinguishing $f(R)$ theories from $\Lambda$CDM are those intrinsically related to the growth of structure, such as weak lensing. At the linear level, the enhancement in the gravitational potential provided by the additional $f(R)$ `fifth force' can separate the theories, whereas at the background level they can be indistinguishable. Under the stringent constraints imposed on the models by Solar System tests and galaxy-formation criteria, we show that the relative difference between the models' linear evolution of the lensing potential will be extremely hard to detect even with future space-based experiments such as {\it Euclid}, with a maximum value of approximately 4% for small scales. We also show the evolution of the gravitational potentials under more relaxed local constraint conditions, where the relative difference between these models and $\Lambda$CDM could prove discriminating.