Novel Probes of Gravity and Dark Energy

TL;DR

This paper reviews novel observational methods for testing gravity and dark energy, emphasizing experiments beyond traditional cosmological probes, with potential to uncover new fundamental physics in the coming decade.

Contribution

It introduces diverse, innovative observational techniques for probing dark energy and modified gravity, expanding beyond conventional methods and highlighting their potential for new physics discoveries.

Findings

Identification of laboratory and astronomical tests for scalar fields and modified gravity.

Comparison of lensing and dynamical masses as a probe of gravity.

Potential for upcoming experiments to detect fundamental physics effects.

Abstract

The discovery of cosmic acceleration has stimulated theorists to consider dark energy or modifications to Einstein's General Relativity as possible explanations. The last decade has seen advances in theories that go beyond smooth dark energy -- modified gravity and interactions of dark energy. While the theoretical terrain is being actively explored, the generic presence of fifth forces and dark sector couplings suggests a set of distinct observational signatures. This report focuses on observations that differ from the conventional probes that map the expansion history or large-scale structure. Examples of such novel probes are: detection of scalar fields via lab experiments, tests of modified gravity using stars and galaxies in the nearby universe, comparison of lensing and dynamical masses of galaxies and clusters, and the measurements of fundamental constants at high redshift. The observational expertise involved is very broad as it spans laboratory experiments, high resolution astronomical imaging and spectroscopy and radio observations. In the coming decade, searches for these effects have the potential for discovering fundamental new physics. We discuss how the searches can be carried out using experiments that are already under way or with modest adaptations of existing telescopes or planned experiments. The accompanying paper on the Growth of Cosmic Structure describes complementary tests of gravity with observations of large-scale structure.