Probing Fundamental Physics with Gravitational Experiments

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In Modern Physics there are two very well accepted theories that describe all of nature. One is the 'Standard Model' which describes all material properties. The Standard Model contains all the quantum particles. The other theory is 'General Relativity', Einstein's theory that describes gravitation. Despite some similarities, these two theories are very different and there is no verified theory or experimental evidence connecting the two, even though most physicists think that there must be a connection. This group specializes on measuring very small forces to conduct ultra-precise tests of gravity. In all the tests carried out by the team, they try to find ever so small deviations from ordinary gravity. If such deviations are found, it would mean that there is more to general relativity, or that this is hint of a third fundamental theory, or that this is a hint of how to unify the Standard Model and General Relativity.Specifically the group is specialized in developing and using torsion balance instruments to1) Test the equivalence principle (EP): It is almost certain that any connection between General Relativity and the Standard Model violates the EP. The torsion balances utilized by the group provide the most precise EP tests to date. The measurement's sensitivity will be doubled, or more, through technical innovation: introducing fused silica fibers and by applying two new methods to track ambient gravity gradients. The experiment's generality and relevance to cosmology will be enhanced by probing the EP with hydrogen-bearing test masses.2) Search for spin-coupled forces and hints of Lorentz violation: Intrinsic spin is fundamental to the standard model interactions but apparently not to general relativity. Leveraging the group's spin-polarized experimental results, constraints will be placed on an emerging class of ultra-light dark matter candidates.3) Test Newton's Inverse-Square (ISL) at short distances: The group's experiments hold the record for the shortest distance at which gravity has been observed, constraining gravity-strength ISL deviation to act over distances less than 42 microns. The group will commission existing upgrades to their 120-fold-symmetric ISL apparatus and press onward to yet smaller distances.4) Advance the frontier of low-frequency small-force technology: Innovative and challenging technology development has underpinned the group's success. Looking to the future of the field, the group will continue to refine both an ultra-low noise cryogenic torsion balance and highly-sensitive, but user-friendly, optical angle-sensing instruments. The creative technical advances required for gravitational strength force measurement at low frequency have had and will have impact on related fields, including gravitational-wave detection. With NSF investment, the group has built up a strong world-leading laboratory with unique expertise and infrastructure in position to address these experimental challenges with efficiency and rigor.