Stringent Constraints on New Pseudoscalar & Vector Bosons from Precision Hyperfine Splitting Measurements

TL;DR

This paper uses precise hyperfine splitting measurements in atoms to set strong constraints on hypothetical pseudoscalar and vector bosons, improving existing limits and highlighting future experimental potential.

Contribution

It introduces a method leveraging specific hyperfine differences to tighten constraints on new bosons, with analysis of existing data and prospects for future measurements.

Findings

Existing Be measurements provide competitive limits for pseudoscalars with masses over 100 keV.

Future Cs measurements could improve constraints by a factor of 2-2.5 for pseudoscalars.

Projected measurements could enhance sensitivity to new vector bosons by an order of magnitude.

Abstract

Axion-like particles and similar new pseudoscalar as well as vector bosons coupled to nucleons and electrons are predicted to lead to spin-dependent forces in atoms and ions. We argue that hyperfine structure measurements in hydrogen- and lithium-like charge states are a sensitive probe to this effect. Employing specific differences of these splittings reduces uncertainties due to nuclear effects in hyperfine structure calculations and measurements. Using this, we show that existing measurements on Be provide competitive limits in the region $m_{\phi}\gtrsim 100\,{\rm keV}$, confirming, or improving by up to a factor of 2, existing constraints for pseudoscalar couplings, depending on the nuclear model. We also find that future measurements on Cs have a further factor of $2-2.5$ improved discovery potential for pseudoscalars and an order of magnitude for new vector bosons when compared with the corresponding current constraints.