Constraining axion coupling constants from measuring the Casimir interaction between polarized test bodies

TL;DR

This paper proposes an experiment to measure the Casimir interaction between polarized silicon carbide plates to constrain axion-neutron coupling constants, potentially improving existing limits on GUT axions through one- and two-axion exchange processes.

Contribution

It derives a general expression for axion-induced pressure between polarized plates and demonstrates how polarization orientation affects the pressure, enabling new constraints on axion-neutron couplings.

Findings

Constraints on axion-neutron coupling are comparable to previous GUT axion limits.

Polarization perpendicular to plates affects the sign and magnitude of the pressure.

Experiment can strengthen existing bounds on axion-neutron coupling constants.

Abstract

We propose an experiment for measuring the effective Casimir pressure between two parallel SiC plates with aligned nuclear spins. The prospective constraints on an axion-neutron coupling constant for both hadronic and GUT axions are calculated using the process of one-axion exchange. For this purpose, a general expression for the additional pressure arising between two polarized plates due to the exchange of one axion between their constituent fermions is derived. We demonstrate that only the polarization component perpendicular to the plates contribute to the pressure. The obtained pressure can be both repulsive and attractive depending on whether the polarizations of both plates are unidirectional or directed in opposite directions. It is shown that although the constraints on an axion-electron coupling obtained in the case of magnetized plates are not competitive, the constraints on an axion-neutron coupling found for plates with polarized nuclear spins are of the same order of magnitude of those obtained previously for the GUT axions alone using the process of two-axion exchange. The proposed experiment allows also to strengthen the presently known constraints on the axion-neutron coupling constants of GUT axions by using both processes of one- and two-axion exchange.