Exploring Exotic Spin-Dependent Interactions via Light Boson Exchange: Theoretical Frameworks and Experimental Techniques in Ferrimagnetic Terbium Iron Garnet*

Exotic force searches play an essential role in exploring physics beyond the Standard Model. The NSR-Ferrimagnets Collaboration has performed experiments utilizing slow neutron polarimetry to search for exotic polarized-neutron polarized-electron interactions in the compensated ferrimagnetic material terbium iron garnet (Tb₃Fe₅0₁₂). Such spin-dependent interactions are frequently used as couplings to weakly-interacting particles, which are motivated as candidates for dark matter and dark energy. An overview of theoretical frameworks for exotic interactions facilitated by light boson exchange will be presented, including existing constraints on exotic coupling constants established through a variety of experimental methods. We will also discuss neutron polarimetry as a well-suited method for conducting exotic force searches and describe our experimental approach from the June 2024 run at the HFIR CG-1D MARS neutron imaging beamline.