Torsion balances set strongest direct limits yet on ultralight dark matter

Key Points:

• An international research team has demonstrated that torsion-balance experiments, originally designed to test the equivalence principle, can be repurposed to detect very light dark matter with masses between 0.01 and 1 eV.
• The study, published in Physical Review Letters, establishes the strongest direct detection limits to date on interactions between light dark matter and nucleons in this mass range.
• The method leverages the high number density and enhanced coherent scattering effects of light dark matter, which induce tiny but measurable accelerations on test masses in torsion-balance apparatuses.
• Experiments with geometrically asymmetric torsion balances are particularly sensitive to these dark-matter-induced accelerations, offering a complementary approach to conventional underground detectors that struggle to detect low-mass dark matter.
• This work highlights the potential of precision measurement experiments to expand the search for dark matter, with future improvements expected to broaden the detectable mass and coupling ranges and deepen the link between particle cosmology and experimental physics.