Constraints on short-range spin-dependent interactions from scalar spin-spin coupling in deuterated molecular hydrogen

TL;DR

This study uses precise measurements of scalar spin-spin interactions in deuterated hydrogen to set new, stringent limits on hypothetical spin-dependent forces mediated by axion-like and axial-vector bosons at atomic scales.

Contribution

It provides the first constraints on pseudoscalar and axial-vector boson couplings from molecular spin interactions, significantly improving previous bounds at atomic distances.

Findings

Constraints on pseudoscalar boson coupling: less than 5×10^{-7} for 5 keV mass.

Constraints on axial-vector boson coupling: less than 2×10^{-19} for ≤1000 eV mass.

Improved bounds by factors of 100 to 10^8 over previous experiments.

Abstract

A comparison between existing measurements and calculations of the scalar spin-spin interaction (J-coupling) in deuterated molecular hydrogen (HD) yields stringent constraints on anomalous spin-dependent potentials between nucleons at the atomic scale (${\rm \sim 1 \AA}$). The dimensionless coupling constant $g_P^pg_P^{N}/4\pi$ associated with exchange of pseudoscalar (axion-like) bosons between nucleons is constrained to be less than $5\times 10^{-7}$ for boson masses in the range of $5 {\rm keV}$. This represents improvement by a factor of about 100 over constraints placed by measurements of the dipole-dipole interaction in molecular ${\rm H_2}$. The dimensionless coupling constant $g_A^pg_A^N/4 \pi$ associated with exchange of a heretofore undiscovered axial-vector boson between nucleons is constrained to be $g_A^pg_A^N/4 \pi < 2 \times 10^{-19}$ for bosons of mass $\lesssim 1000 {\rm eV}$, improving constraints at this distance scale by a factor of 100 for proton-proton couplings and more than 8 orders of magnitude for neutron-proton couplings. This limit is also a factor of 100 more stringent than recent constraints obtained for axial-vector couplings between electrons and nucleons obtained from comparison of measurements and calculations of hyperfine structure.