Stronger constraints on the pseudoscalar coupling constants of an axion and axion-like particles with a proton and a neutron are obtained from measurements of the thermal Casimir-Polder force between a Bose-Einstein condensate of ${}^{87}\mathrm{Rb}$ atoms and a ${\mathrm{SiO}}_2$ plate. For this purpose, the additional force acting between a condensate cloud and a plate due to two-axion exchange is calculated. The obtained constraints refer to the axion masses from 0.1 meV to 0.3 eV which overlap with the region from 0.01 to 10 meV considered at the moment as the most prospective.

• Received 6 December 2013

DOI:https://doi.org/10.1103/PhysRevD.89.035010