Short-range spin-dependent interactions of electrons: a probe for exotic pseudo-Goldstone bosons

TL;DR

This study used a torsion pendulum with specialized electron-spin distributions to set new laboratory bounds on exotic pseudo-Goldstone bosons and $CP$-violating interactions, reaching unprecedented sensitivity.

Contribution

It provides the highest laboratory constraints to date on pseudo-Goldstone bosons and $CP$-violating monopole-dipole interactions, improving previous bounds significantly.

Findings

Set new upper limits on pseudo-Goldstone boson interactions.

Improved bounds on $CP$-violating monopole-dipole interactions by up to 1000 times.

Reached symmetry-breaking scales up to 70 TeV.

Abstract

We used a torsion pendulum and rotating attractor with 20-pole electron-spin distributions to probe dipole-dipole interactions mediated by exotic pseudo-Goldstone bosons with $m_{\rm b}\leq 500 \; \mu$eV and coupling strengths up to 14 orders of magnitude weaker than electromagnetism. This corresponds to symmetry-breaking scales $F \leq 70$ TeV, the highest reached in any laboratory experiment. We used an attractor with a 20-pole unpolarized mass distribution to improve laboratory bounds on $CP$-violating monopole-dipole interactions with $1.5\:\mu$eV$<m_{\rm b}<400\:\mu$eV by a factor of up to 1000.