Imprint of f(R) gravity in the cosmic magnification

TL;DR

This paper investigates how f(R) gravity, particularly the Hu-Sawicki model, affects cosmic magnification on large scales, revealing potential observational signatures and the importance of relativistic effects in cosmological measurements.

Contribution

It provides the first detailed analysis of large-scale cosmic magnification in f(R) gravity, highlighting distinctive patterns related to the model's parameters and relativistic effects.

Findings

Large-scale behavior of cosmic magnification depends on the exponent n in f(R) models.

Relativistic effects cause suppression or boost of magnification depending on redshift.

Distinct patterns in magnification could serve as observational tests for f(R) gravity.

Abstract

f(R) gravity is one of the simplest viable modifications to General Relativity: it passes local astrophysical tests, predicts both the early-time cosmic inflation and the late-time cosmic acceleration, and also describes dark matter. In this paper, we probe cosmic magnification on large scales in f(R) gravity, using the well-known Hu-Sawicki model as an example. Our results indicate that at redshifts z < 3, values of the model exponent n > 1 lead to inconsistent behaviour in the evolution of scalar perturbations. Moreover, when relativistic effects are taken into account in the large scale analysis, our results show that as z increases, large-scale changes in the cosmic magnification angular power spectrum owing to integral values of n tend to share a similar pattern, while those of decimal values tend to share another. This feature could be searched for in the experimental data, as a potential "smoking gun" for the given class of gravity models. Furthermore, we found that at z = 1 and lower, relativistic effects lead to a suppression of the cosmic magnification on large scales in f(R) gravity, relative to the concordance model; whereas, at z > 1, relativistic effects lead to a relative boost of the cosmic magnification. In general, relativistic effects enhance the potential of the cosmic magnification as a cosmological probe.