Comment on "Viable singularity-free f(R) gravity without a cosmological constant" [arXiv:0905.1941]

TL;DR

This paper critically examines a proposed f(R) gravity model claiming to be cosmologically viable, revealing it conflicts with local gravity constraints and SDSS data, thus questioning its viability as an alternative to LCDM.

Contribution

It provides a critical analysis showing that the proposed f(R) model fails to meet local gravity and observational constraints despite satisfying some theoretical conditions.

Findings

Fails to satisfy local gravity constraints

Conflicts with SDSS matter power spectrum data

Does not provide a viable alternative to LCDM

Abstract

A modified f(R) gravity model has been recently proposed in Phys. Rev. Lett. 102, 221101 (2009) [arXiv:0905.1941] whose cosmological behaviour is clearly distinguishable from LCDM. Contrary to previous opinions which consider that self-consistent f(R) gravity models distinct from LCDM are almost ruled out, the authors claim that the proposed model is cosmologically viable. Here we show that although the model satisfies some consistency conditions, precisely because of its departure from LCDM behaviour, it does not satisfy local gravity constraints and, in addition, the predicted matter power spectrum conflicts with SDSS data.