Astrophysical observations and cosmological data give strong evidence that nearly a quarter of the Universe consists of dark matter. There are strong reasons to believe that it cannot consist of known particles. It is likely that the dark matter consists of new particles that have not yet revealed themselves in any other context. There are two well-motivated possibilities for the dark-matter particles: heavy fermionic particles called WIMPs and bosonic ultra-light dark matter (ULDM), of which axions are a subset. Searches at large-scale facilities for WIMPs have not yet found dark matter. Recent theoretical suggestions have inspired searches for ULDM particles with masses as low as 10^(-23) eV/c2. These particles are not detected individually, but rather by the coherent fields they produce, which are most-readily detected in small-scale precision experiments. The torsion balance technology developed by the Eöt-Wash Gravity Group is ideally suited to search for the effects expected from these bosonic fields. The group has a long tradition of teaching research to undergraduate students, graduate students, and postdocs. With formal and informal instruction this project will provide broad STEM education at all levels. This project offers unique training opportunities in fundamental physics, realization of precision mechanical instruments, and the execution of precision measurements. The technology developed is finding application in gravitational wave detection as well as in applied areas such as seismology.

Torsion balances have become sensitive enough to be significant tools in the search for ULDM. Recently, such measurements have set some of the most stringent limits on axion-like and equivalence-principle-violating ULDM. Enabled by technological advances, this torsion balance search will encompass upgrades to existing instruments that make these dark matter searches substantially more sensitive. In addition, data analysis will be performed to look for the signature of equivalence-principle-violating bosonic ULDM in the data stream of concurrent torsion-balance tests of gravity. This award will fund searches for this bosonic ULDM using rotating and stationary torsion balances, using beryllium and polyethylene test materials to increase ULDM sensitivity; searches for spin-coupled axion-like ULDM using an existing unique spin-polarized torsion pendulum in an upgraded stationary torsion balance; and increase experimental sensitivity to ULDM signals by refining fused-silica fibers, adding auxiliary sensors, upgrading readout, and improving instrumental shielding.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

National Science Foundation (NSF)
Division of Physics (PHY)
Application #
Program Officer
Jonathan Whitmore
Project Start
Project End
Budget Start
Budget End
Support Year
Fiscal Year
Total Cost
Indirect Cost
University of Washington
United States
Zip Code