  We consider different types of Q-balls as self-interacting dark matter. For
the Q-balls to act as the dark matter of the universe they should not
evaporate, which requires them to carry very large charges; depending on the
type, the minimum charge could be as high as Q \sim 10^{33} or the Q-ball
coupling to ordinary matter as small as \sim 10^{-35}. The
cross-section-to-mass ratio needed for self-interacting dark matter implies a
mass scale of m \sim O(1) MeV for the quanta that the Q-balls consist of, which
is very difficult to achieve in the MSSM.
