Bounds on the Coupling of Light Pseudoscalars to Nucleons from Optical Laser Experiments

Abstract

We find the following improved laboratory bounds on the coupling of light pseudoscalars to protons and neutrons: $g_p^2/4\pi < 1.7 \times 10^{-9}$ and $g_n^2/4\pi < 6.8 \times 10^{-8}$. The limit on $g_p$ arises since a nonzero $g_p$ would induce a coupling of the pseudoscalar to two photons, which is limited by experiments studying laser beam propagation in magnetic fields. Combining our bound on $g_p$ with a recent analysis of Fischbach and Krause on two-pseudoscalar exchange potentials and experiments testing the equivalence principle, we obtain our limit on $g_n$. (PACS number(s): 14.20.Dh/14.80.-j/12.20.Fv/04.90.+e)