Self-consistent theory of instabilities in the spin-1 Bose gas

We discuss instabilities of a spin-1 Bose condensate using a Hartree-Fock-Bogoliubov approximation to account for the interactions between the unstable modes. There is a close analogy to the ``S-theory'' that describes parametric excitation of magnons in solid state systems. We particularly emphasize the pair-breaking effect of phase fluctuations in the parent condensate and their role in inhibiting the instability.