Experimental Identification of Nonpointlike Dark-Matter Candidates

We show that direct dark-matter detection experiments can distinguish between pointlike and nonpointlike dark-matter candidates. The shape of the nuclear recoil-energy spectrum from pointlike dark-matter particles, e.g., neutralinos, is determined by the velocity distribution of dark matter in the galactic halo and by nuclear form factors. Typical cross sections of nonpointlike dark matter, for example, Q-balls, have a new form factor, which decreases rapidly with the recoil energy. A signal from nonpointlike dark matter is expected to peak near the experimental threshold and to fall off rapidly at higher energies.