Collisional Dark Matter and Scalar Phantoms

As has been previously proposed, a minimal modification of the standard $SU(3)\times SU(2)\times U(1)$ theory provides a viable dark matter candidate. Such a particle, a scalar gauge singlet, is naturally self-interacting---making it of particular interest given recent developments in astrophysics. We review this dark matter candidate, with reference to the parameter ranges currently under discussion.