Testing Gravity using Void Profiles

TL;DR

This paper explores how void properties in $f(R)$ gravity models differ from General Relativity, proposing weak lensing as a method to detect these differences and constrain modified gravity parameters.

Contribution

It demonstrates that void profiles and lensing signals can distinguish $f(R)$ gravity models from GR, providing a new observational approach to test gravity theories.

Findings

Void profiles in $f(R)$ models are steeper and more empty of dark matter.

Weak lensing can differentiate $f(R)$ parameters $|f_{R0}|=10^{-5}$ and $10^{-4}$ from GR with high significance.

Large volume surveys are needed to detect smaller $|f_{R0}|$ values like $10^{-6}$.

Abstract

We investigate void properties in $f(R)$ models using N-body simulations, focusing on their differences from General Relativity (GR) and their detectability. In the Hu-Sawicki $f(R)$ modified gravity (MG) models, the halo number density profiles of voids are not distinguishable from GR. In contrast, the same $f(R)$ voids are more empty of dark matter, and their profiles are steeper. This can in principle be observed by weak gravitational lensing of voids, for which the combination of a spectroscopic redshift and a lensing photometric redshift survey over the same sky is required. Neglecting the lensing shape noise, the $f(R)$ model parameter amplitudes $|f_{R0}|=10^{-5}$ and $10^{-4}$ may be distinguished from GR using the lensing tangential shear signal around voids by 4 and 8$\sigma$ for a volume of 1~(Gpc/$h$)$^3$. The line-of-sight projection of large-scale structure is the main systematics that limits the significance of this signal for the near future wide angle and deep lensing surveys. For this reason, it is challenging to distinguish $|f_{R0}|=10^{-6}$ from GR. We expect that this can be overcome with larger volume. The halo void abundance being smaller and the steepening of dark matter void profiles in $f(R)$ models are unique features that can be combined to break the degeneracy between $|f_{R0}|$ and $\sigma_8$.