Constraints on exotic spin-dependent interactions between electrons from helium fine-structure spectroscopy

TL;DR

This paper uses helium-4 spectroscopy to set new limits on exotic spin-dependent interactions between electrons, significantly improving constraints on pseudoscalar boson exchanges and establishing first atomic-scale bounds on velocity-dependent interactions.

Contribution

It provides the first atomic-scale constraints on certain velocity-dependent exotic interactions and improves existing bounds on pseudoscalar boson exchanges by a factor of about 100.

Findings

Enhanced constraints on pseudoscalar boson exchange interactions.

First atomic-scale limits on velocity-dependent dipole-dipole interactions.

Improved bounds for interactions with boson masses between 10^{-2} eV and 10^{4} eV.

Abstract

Agreement between theoretical calculations of atomic structure and spectroscopic measurements is used to constrain possible contribution of exotic spin-dependent interactions between electrons to the energy differences between states in helium-4. In particular, constraints on dipole-dipole interactions associated with the exchange of pseudoscalar bosons (such as axions or axion-like particles, ALPs) with masses $10^{-2}~{\rm eV} \lesssim m \lesssim 10^{4}~{\rm eV}$ are improved by a factor of $\sim 100$. The first atomic-scale constraints on several exotic velocity-dependent dipole-dipole interactions are established as well.