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Dark-Matter Electric and Magnetic Dipole Moments

We consider the consequences of a neutral dark-matter particle with a nonzero electric and/or magnetic dipole moment. Theoretical constraints, as well as constraints from direct searches, precision tests of the standard model, the cosmic microwave background and matter power spectra, and cosmic gamma rays, are included. We find that a relatively light particle with mass between an MeV and a few GeV and an electric or magnetic dipole as large as $\sim 3\times 10^{-16}e$ cm (roughly $1.6\times10^{-5} μ_B$) satisfies all experimental and observational bounds. Some of the remaining parameter space may be probed with forthcoming more sensitive direct searches and with the Gamma-Ray Large Area Space Telescope.