Probing Dark Energy on the Moon

TL;DR

Using lunar laser interferometry to measure horizon-scale metric fluctuations offers a novel way to directly constrain the kinetic operators of dark energy's effective field theory, advancing understanding of cosmic acceleration.

Contribution

This work introduces a new observational method employing lunar laser interferometry to probe the kinetic sector of dark energy EFT, which was previously weakly constrained.

Findings

Sensitivity to the EFT kinetic coefficient $M_2^4$

Ability to measure dark energy sound speed $c_s^2$

Potential to constrain or discover new dark energy models

Abstract

The effective field theory (EFT) of cosmic acceleration provides a model-independent framework for describing dark energy and modified gravity, yet many of its defining operators remain weakly constrained by existing observations. We show that measurements of horizon-scale metric fluctuations with a lunar laser interferometer can directly probe the kinetic sector of the EFT of dark energy, enabling constraints on operators governing scalar perturbation dynamics rather than only the background expansion history. In particular, we demonstrate sensitivity to the EFT kinetic coefficient $M_2^4$ and the associated sound speed of dark energy, $c_s^2$. This establishes a qualitatively new observational handle on the microphysical consistency conditions of late-time acceleration models, allowing broad regions of EFT parameter space to be probed, constrained, or potentially discovered.