Torsion-balance probes of fundamental physics

This white paper is submitted as part of Snowmass2013 (subgroup CF2). The extraordinary sensitivity of torsion-balances can be used to search for the ultra-feeble forces suggested by attempts to unify gravity with the other fundamental interactions. The motivation, the results and their implications as well as the future prospects of this work are summarized. The experiments include tests of the universality of free fall (weak equivalence principle), probes of the short-distance behavior of gravity (inverse-square law tests for extra dimensions and exchange forces from new meV scale bosons), and Planck-scale tests of Lorentz invariance (preferred-frame effects, non-commutative geometries).