Constraints on anomalous spin-spin interactions from spin-exchange collisions

TL;DR

This study uses measurements of spin-exchange collisions between alkali atoms and noble gases to set new limits on hypothetical spin-dependent forces and interactions at the atomic scale, including constraints on neutron couplings and torsion gravity.

Contribution

It provides novel experimental constraints on anomalous spin-spin interactions and related forces, improving bounds on neutron couplings and torsion gravity effects.

Findings

Constraints on neutron axial vector coupling: $g_A^n/ ext{sqrt}(4 ext{pi} ext{hc}) < 2 imes 10^{-3}$

Limits on velocity- and spin-dependent interactions involving nuclear spins and relative velocity

Bounds on torsion gravity effects at atomic scales

Abstract

Measured and calculated cross sections for spin-exchange between alkali atoms and noble gases (specifically sodium and helium) are used to constrain anomalous spin-dependent forces between nuclei at the atomic scale ($\sim 10^{-8}~{\rm cm}$). Combined with existing stringent limits on anomalous short-range, spin-dependent couplings of the proton, the dimensionless coupling constant for a heretofore undiscovered axial vector interaction of the neutron arising from exchange of a boson of mass $\lesssim 100~{\rm eV}$ is constrained to be $g_A^n/\sqrt{4 \pi \hbar c} < 2 \times 10^{-3}$. Constraints are established for a velocity- and spin-dependent interaction $\propto \prn{\mathbf{I} \cdot \mathbf{v}} \prn{\mathbf{K} \cdot \mathbf{v}}$, where $\mathbf{I}$ and $\mathbf{K}$ are the nuclear spins of He and Na, respectively, and $\mathbf{v}$ is the relative velocity of the atoms. Constraints on torsion gravity are also considered.