2019-05-31 11:00  P7F

Experimental Searches for Sub-Millimeter Range Fifth Forces

Joshua Long

Current experimental limits allow for fundamental forces of nature millions of times stronger than gravity at distance ranges below 1 mm. Physics beyond the Standard Model predicts a variety of phenomena in this range, including signatures of extra spacetime dimensions, scalars motivated by string theory, violations of Lorentz symmetry, and dark energy and dark matter. The latter includes the axion, a light pseudoscalar motivated by the strong CP problem of QCD, which could couple to spin. In this talk I will discuss several experimental searches in progress at Indiana University, which are sensitive to fifth forces that couple to both mass and spin. The first uses planar, 1 kHz mechanical oscillators as test masses with a stiff conducting shield in between them to suppress backgrounds. This experiment is being modified to search for spin-dependent forces by augmenting the test masses with a polarized material which exhibits orbital compensation of the magnetism associated with the electron spins, substantially reducing the magnetic backgrounds. Another experiment, using NMR techniques to probe the interaction between a dense, non-magnetic source and a sample of polarized helium-3 atoms, is expected to further improve the sensitivity to axion-mediated forces by several orders of magnitude.