Equivalence Principle Tests and Direct Searches for Ultra-Light Dark Matter with Fused-Silica Torsion Fibers

Abstract

Torsion balances are precision instruments for testing gravity and other experiments. However, they are limited by thermal noise and angular readout noise. This dissertation presents research and development in producing and using fused-silica fibers, which can achieve much lower thermal noise. Employing these fibers, we demonstrate significantly improved sensitivity compared to the tungsten fibers we have traditionally used. Combined with new analysis techniques, we used the fibers to perform a dark matter experiment, resulting in new ultra-light dark matter limits. We also demonstrate significant progress towards an improved equivalence principle test. Looking to the future, we can use these fibers to enable various scientific campaigns that significantly improve on important constraints.