Imprint of f(R) gravity in the cosmic magnification

Abstract

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 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 $z \, {\lt }\, 3$, values of the model exponent $n \, {\gt }\, 1$ lead to inconsistent behaviour in the evolution of the 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 $z \, {\gt }\, 1$, 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.