| Interactions that involve the coupling of a particle's intrinsic spin independent of its magnetic moment have been postulated, but never detected. This dissertation describes a precision search for spin-coupled forces that arise in the context of broken Lorentz and CPT symmetries, exotic particle exchange, non-commutative geometries, and torsion gravity. We used a torsion pendulum containing 9.8 x 1022 polarized electron spins to search for interactions between the pendulum's electrons and a vector field fixed in inertial space, a condensate of exotic particles defining a preferred frame in the universe, unpolarized matter in the laboratory's environment and the sun, and polarized matter in spin sources placed near to the pendulum. We have seen no evidence for these spin-coupled interactions. The measurements reported here constrain the energy required to flip an electron spin about directions fixed in inertial space to be ≲ 10-22 eV. We have used these constraints to place limits on preferred-frame effects and exotic boson exchange that are up to four orders of magnitude lower than the previous reported limits, and we present the first limits on dynamical effects associated with broken Lorentz symmetry. This dissertation describes the torsion balance apparatus used to perform these measurements, as well as the analysis of experimental data and systematic effects, and the corresponding results. |
