Designing Surveys for Tests of Gravity

TL;DR

This paper emphasizes expanding observational strategies to test gravity theories on astrophysical scales, focusing on signatures outside the linear regime and utilizing galaxy and cluster surveys with lensing and spectroscopy.

Contribution

It identifies new observational regimes and signatures for testing gravity beyond the linear regime, proposing survey strategies involving galaxy halos, spectroscopy, and lensing.

Findings

Screening mechanisms operate inside halos like the Milky Way.

New regimes for testing gravity can be targeted by cosmological surveys.

Combining lensing and dynamical data enhances gravity tests.

Abstract

Modified gravity theories may provide an alternative to dark energy to explain cosmic acceleration. We argue that the observational program developed to test dark energy needs to be augmented to capture new tests of gravity on astrophysical scales. Several distinct signatures of gravity theories exist outside the linear regime, especially owing to the screening mechanism that operates inside halos like the Milky Way to ensure that gravity tests in the solar system are satisfied. This opens up several decades in length scale and new classes of galaxies at low-redshift that can be exploited by surveys. While theoretical work on models of gravity is in the early stages, we can already identify new regimes which cosmological surveys could target to test gravity. These include: 1. A small scale component that focuses on the interior and vicinity of galaxy and cluster halos. 2. Spectroscopy of low redshift galaxies, especially galaxies smaller than the Milky Way, in environments that range from voids to clusters. 3. A program of combining lensing and dynamical information, from imaging and spectroscopic surveys respectively, on the same (or statistically identical) sample of galaxies.