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Probing Dark Energy on the Moon

Alfredo Gurrola, Robert J. Scherrer, Oem Trivedi

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.

Probing Dark Energy on the Moon

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 and the associated sound speed of dark energy, . 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.
Paper Structure (7 sections, 17 equations, 3 figures)

This paper contains 7 sections, 17 equations, 3 figures.

Table of Contents

  1. Introduction
  2. Effective Field Theory of Dark Energy
  3. Horizon-Scale Metric Fluctuations as an EFT Probe
  4. Mock Strain Power Spectra
  5. Forecast Methodology
  6. EFT Constraints and Parameter Space
  7. Discussion and Conclusions

Figures (3)

  • Figure 1: Fisher contour ellipses in the $(\tilde{M}_2^{4},c_s^2)$ plane for a lunar laser interferometer, centered on the fiducial clustering dark energy model $(w,c_s^2)=(-1,10^{-2})$. Shown are the joint 1$\sigma$ and 2$\sigma$ confidence regions obtained using the cosmology-calibrated mock strain power spectrum mapped onto the EFT phase space. $\Lambda(t)$ was chosen to reproduce the desired $\Lambda$CDM-like evolution, and the braiding and extrinsic-curvature coefficients were held fixed, consistent with existing gravitational-wave propagation and large-scale structure bounds.
  • Figure 2: Fisher contour ellipses in the $(\tilde{M}_2^{4},c_s^2)$ plane for a lunar laser interferometer, centered on the fiducial clustering dark energy model $(w,c_s^2)=(-1,10^{-2})$. Shown are the joint 1$\sigma$ and 2$\sigma$ confidence regions obtained using the cosmology-calibrated mock strain power spectrum mapped onto the EFT phase space. A Gaussian prior is assumed for the equation-of-state parameter, restricting it to within 3% of $w=-1$, the braiding parameter is allowed to vary freely, and no additional constraints are imposed on the parameters governing the background expansion history.
  • Figure 3: Fisher contour ellipses in the $(\tilde{M}_2^{4},c_s^2)$ plane for a lunar laser interferometer, centered on the fiducial clustering dark energy model $(w,c_s^2)=(-1,10^{-2})$, with all EFT parameters allowed to vary freely in the likelihood analysis. Shown are the joint 1$\sigma$ and 2$\sigma$ confidence regions obtained using the cosmology-calibrated mock strain power spectrum mapped onto the EFT phase space.