Detecting meV-scale dark matter via coherent scattering with an asymmetric torsion balance

Dark matter with mass in the crossover range between wave dark matter and particle dark matter, around <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mo stretchy="false">(</a:mo><a:msup><a:mn>10</a:mn><a:mrow><a:mo>−</a:mo><a:mn>3</a:mn></a:mrow></a:msup><a:mo>,</a:mo><a:msup><a:mn>10</a:mn><a:mn>3</a:mn></a:msup><a:mo stretchy="false">)</a:mo><a:mtext> </a:mtext><a:mtext> </a:mtext><a:mi>eV</a:mi></a:math>, remains relatively unexplored by terrestrial experiments. In this mass regime, dark matter scatters coherently with macroscopic objects. The effect of the coherent scattering greatly enhances the accelerations of the targets caused from dark matter collisions by a factor of <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"><e:mo>∼</e:mo><e:msup><e:mn>10</e:mn><e:mn>23</e:mn></e:msup></e:math>. We propose a novel torsion balance experiment with test bodies of different geometric sizes to detect such dark-matter-induced acceleration. This method could provide the strongest sensitivity on the scattering cross section between the dark matter and a nucleon in the mass range of <g:math xmlns:g="http://www.w3.org/1998/Math/MathML" display="inline"><g:mo stretchy="false">(</g:mo><g:msup><g:mn>10</g:mn><g:mrow><g:mo>−</g:mo><g:mn>3</g:mn></g:mrow></g:msup><g:mo>,</g:mo><g:mn>1</g:mn><g:mo stretchy="false">)</g:mo><g:mtext> </g:mtext><g:mtext> </g:mtext><g:mi>eV</g:mi></g:math>.