Direct detection of dark matter in universal bound states
  We study the signatures for internal structure of dark matter in direct
detection experiments in the context of asymmetric self-interacting dark
matter. The self-interaction cross section of two dark matter particles at low
energies is assumed to come close to saturating the S-wave unitarity bound,
which requires the presence of a resonance near their scattering threshold. The
universality of S-wave near-threshold resonances then implies that the
low-energy scattering properties of a two-body bound state of dark matter
particles are completely determined by its binding energy, irrespective of the
underlying microphysics. The form factor for elastic scattering of the bound
state from a nucleus and the possibility of breakup of the bound state produce
new signatures in the nuclear recoil energy spectrum. If these features are
observed in experiments, it will give a smoking-gun signature for the internal
structure of dark matter.
