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A recent article on probing Earth's interior mentioned the potential use of a "fifth force", long range electron spin-spin interactions, as a tool in the endeavor. Has anybody published any experimental results confirming detection of this "force'? Is existence of long range spin-spin interaction compatible with current quantum mechanics theory?

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I found this Many particle-physics models that extend the standard model predict the existence of long-range spin-spin interactions. We propose an approach that uses the Earth as a polarized spin source to investigate these interactions. Using recent deep-Earth geophysics and geochemistry results, we create a comprehensive map of electron polarization within the Earth induced by the geomagnetic field. We examine possible long-range interactions between these spin-polarized geoelectrons and the spin-polarized electrons and nucleons in three laboratory experiments. By combining our model and the results from these experiments, we establish bounds on torsion gravity and possible long-range spin-spin forces associated with the virtual exchange of either spin-one axial bosons or unparticles.

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This sort of thing would show up in experiments as a violation of the equivalence principle. There are strict upper limits on such effects (e.g., Heckel 2006, which used a spin-polarized torsion pendulum), and the Amherst-UT group also gets a null result. A positive result from such an experiment might be evidence for gravitational torsion, or, according to the Heckel paper, "Spin-dependent forces are also generically produced by the exchange of pseudoscalar particles."


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