Shedding Light on Dark Matter: A Faraday Rotation Experiment to Limit a Dark Magnetic Moment

I describe a new possibility for the direct detection of dark matter. That is, if dark matter consists, in part, of cold, neutral particles with a non-zero magnetic moment, then, in the presence of an external magnetic field, a measurable gyromagnetic Faraday effect becomes possible. A Faraday rotation experiment can set limits on the magnetic moment of a electrically-neutral, dark-matter particle, and the limits increase in stringency as the candidate mass decreases. I describe how such could be realized and determine the limits on the magnetic moment as a function of mass which follow given demonstrated experimental capacities.