[Paper Review] Novel Probes of Gravity and Dark Energy

Bhuvnesh Jain, Austin Joyce+30 more|arXiv (Cornell University)|Sep 20, 2013

Space Science and Extraterrestrial Life19 citations

TL;DR

This paper proposes a suite of novel observational probes to test modified gravity and dark energy beyond standard ΛCDM, focusing on fifth-force signatures, screening mechanisms, and deviations in gravitational lensing and dynamical mass. It outlines laboratory experiments, high-resolution astrophysical observations, and high-redshift measurements to detect scalar fields and test gravity at cosmological scales, offering a complementary approach to conventional large-scale structure and distance-redshift probes.

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.

Motivation & Objective

• To identify and develop observational tests sensitive to modified gravity and dark energy beyond smooth dark energy models.
• To address the challenge of fifth forces in modified gravity by focusing on screening mechanisms that hide them in dense environments like the solar system.
• To explore observational signatures of scalar fields and dark sector couplings through diverse experimental approaches.
• To complement large-scale structure and expansion history probes with new tests sensitive to gravity's behavior across cosmic and astrophysical scales.
• To guide the next decade's experimental program using existing or modestly adapted facilities and ongoing experiments.

Proposed method

• Use laboratory experiments to detect light scalar fields and fifth forces, leveraging precision tests of gravity at sub-millimeter to meter scales.
• Apply high-resolution astronomical imaging and spectroscopy to compare weak gravitational lensing and dynamical mass profiles in galaxies and clusters.
• Constrain modified gravity models using the discrepancy between lensing and dynamical mass, particularly in the context of screening mechanisms.
• Measure variations in fundamental constants at high redshift using quasar absorption spectra to probe time-varying scalar fields.
• Analyze scalar field equations of motion with screening mechanisms (e.g., chameleon, symmetron, Vainshtein) to predict observable signatures.
• Utilize existing or adapted telescopes and experiments—such as GammeV, CAST, and ground-based optical/infrared facilities—for targeted observations.

Experimental results

Research questions

• RQ1 What observational signatures distinguish modified gravity models with screening mechanisms from general relativity?
• RQ2 How can fifth-force signals be detected in laboratory experiments despite their suppression in the solar system?
• RQ3 To what extent do discrepancies between lensing and dynamical mass in galaxies and clusters signal new gravitational physics?
• RQ4 Can variations in fundamental constants at high redshift provide evidence for scalar fields in the dark sector?
• RQ5 What are the most sensitive and feasible experimental pathways to test modified gravity in the next decade?

Key findings

• Laboratory experiments such as GammeV and CAST have placed constraints on light scalar fields and fifth forces, with sensitivities reaching sub-millimeter scales.
• High-precision measurements of lensing and dynamical mass in galaxies and clusters show consistent deviations from general relativity predictions in some systems, suggesting potential fifth-force signals.
• Quasar absorption line studies at high redshift (e.g., from VLT and Keck telescopes) have constrained variations in the fine-structure constant Δα/α ≲ 10−5 over cosmic time.
• Screening mechanisms like the chameleon and Vainshtein effects successfully suppress fifth forces in dense environments, allowing modified gravity models to pass solar system tests.
• Theoretical models such as f(R) gravity and massive gravity predict specific signatures in lensing and structure growth that can be tested with upcoming surveys.
• The combination of multiple probes—laboratory, astrophysical, and cosmological—provides a robust, multi-scale approach to detecting new physics beyond ΛCDM.