Spatial variation of fundamental couplings and Lunar Laser Ranging

TL;DR

This paper demonstrates that lunar laser ranging can detect cosmic spatial variations in fundamental constants, providing a sensitive test for new physics beyond the Standard Model and complementing other equivalence principle experiments.

Contribution

It introduces a novel application of lunar laser ranging to constrain spatial variations of fundamental constants, linking local measurements to cosmological gradients.

Findings

Lunar laser ranging can detect gradients of fundamental constants at the level of 2.6 x 10^-6 Glyr^-1.

Current and planned equivalence principle tests can probe similar cosmic gradients.

The method provides a new way to test for spatial variation of fundamental constants across the universe.

Abstract

If the fundamental constants of nature have a cosmic spatial variation, there will in general be extra forces with a preferred direction in space which violate the equivalence principle. We show that the millimeter-precision Apache Point Observatory Lunar Laser-ranging Operation provides a very sensitive probe of such variation that has the capability of detecting a cosmic gradient of the ratio between the quark masses and the strong interaction scale at the level with the gradient of ln (m_quark/Lambda_QCD) ~ 2.6 x 10^-6 Glyr^-1, which is comparable to the cosmic gradients suggested by the recently reported measurements of Webb et al. We also point out the capability of presently planned improved equivalence principle tests, at the Delta g/g < 10^-17 level, to probe similar cosmic gradients.