Constraints on Light Pseudoscalars Implied by Tests of the Gravitational Inverse-Square Law

TL;DR

This paper derives new experimental limits on the coupling of light pseudoscalars to neutrons and protons by analyzing violations of the gravitational inverse-square law and the weak equivalence principle, constraining new physics beyond the Standard Model.

Contribution

It provides the first direct experimental limit on pseudoscalar-neutron coupling and improves existing bounds on pseudoscalar-proton coupling using gravitational tests.

Findings

New limit on pseudoscalar-neutron coupling: g_n^2/4pi < 1.6 × 10^-7

Improved bounds on pseudoscalar-proton coupling

Constraints suggest pseudoscalars are weakly coupled to matter

Abstract

The exchange of light pseudoscalars between fermions leads to a spin-independent potential in order g^4, where g is the Yukawa pseudoscalar-fermion coupling constant. This potential gives rise to detectable violations of both the weak equivalence principle (WEP) and the gravitational inverse-square law (ISL), even if g is quite small. We show that when previously derived WEP constraints are combined with those arisingfrom ISL tests, a direct experimental limit on the Yukawa coupling of light pseudoscalars to neutrons can be inferred for the first time (g_n^2/4pi < 1.6 \times 10^-7), along with a new (and significantly improved) limit on the coupling of light pseudoscalars to protons.