Torsion Balance Experiments Enable Direct Detection of Sub-eV Dark Matter

TL;DR

This paper demonstrates that existing torsion balance experiments can directly detect sub-eV dark matter through induced accelerations, providing new constraints on dark matter-nucleon interactions.

Contribution

It shows that current torsion balances, originally designed for the Equivalence Principle, can be used to set the most stringent limits on sub-eV dark matter scattering.

Findings

Existing torsion balances constrain dark matter-nucleon scattering in the (0.01, 1) eV mass range.

Torsion balances with geometric asymmetry are sensitive to dark matter-induced accelerations.

Reanalysis of existing experiments yields new bounds on light dark matter interactions.

Abstract

Light dark matter with sub-eV masses has a high number density in our galaxy, and its scattering cross section with macroscopic objects can be significantly enhanced by coherence effects. Repeated scattering with a target object can induce a measurable acceleration. Torsion balance experiments with geometric asymmetry are, in principle, capable of detecting such signals. Our analysis shows that existing torsion balances designed to test the Equivalence Principle already place the most stringent constraints on DM-nucleon scattering in the $(10^{-2}, 1)\,$eV mass range.