Ionization feedback mechanism in the recombination era of the Universe

The 2-fluid radiation hydrodynamics during and before the recombination era are investigated within the cosmological standard models of the universe. It is found that if all nonlinearities (with the exception of those contained in the coupling term between the two fluids) via the degree of ionization are neglected, there exists a strong feedback mechanism on the unstable modes which prevents them from growing if their relative amplitudes of density contrast have values on the order of 0.10-0.01. The nonlinear equations are solved numerically by an adiabatic elimination technique normally used in self-organization problems.