  We study the nonequilibrium dynamics of an electronic model with competing
spin-density-wave and unconventional superconductivity in the context of iron
pnictides. Focusing on the collisionless regime, we find that magnetic and
superconducting order parameters may coexist dynamically after a sudden quench,
even though the equilibrium thermodynamic state supports only one order
parameter. We consider various initial conditions concomitant with the phase
diagram and in a certain regime identify different oscillatory amplitude modes
with incommensurate frequencies for magnetic and superconducting responses. At
the technical level we solve the equations of motion for the electronic Green's
functions and self-consistency conditions by reducing the problem to a closed
set of Bloch equations in a pseudospin representation. For certain quench
scenarios the nonadiabatic dynamics of the pairing amplitude is completely
integrable and in principle can be found exactly.
