  We investigate the interplay between the magnetic and the superconducting
degrees of freedom in unconventional multi-band superconductors such as iron
pnictides. For this purpose a dynamical mode-mode coupling theory is developed
based on the coupled Bethe-Salpeter equations. In order to investigate the
region of the phase diagram not too far from the tetracritical point where the
magnetic spin density wave, (SDW) and superconducting (SC) transition
temperatures coincide, we also construct a Ginzburg - Landau functional
including both SC and SDW fluctuations in a critical region above the
transition temperatures. The fluctuation corrections tend to suppress the
magnetic transition, but in the superconducting channel the intraband and
interband contribution of the fluctuations nearly compensate each other.
