BOUND PAIRS OF FRONTS IN A REAL GINZBURG-LANDAU EQUATION COUPLED TO AMEAN-FIELD

Motivated by the observation of localized traveling-wave states ('puls es') in convection in binary liquid mixtures, the interaction of front s is investigated in a real Ginzburg-Landau equation which is coupled to a mean field. In that system the Ginzburg-Landau equation describes the traveling-wave amplitude and the mean field corresponds to a conc entration mode which arises due to the slowness of mass diffusion. It is shown that for single fronts the mean field can lead to a hystereti c transition between slow and fast fronts. Its contribution to the int eraction between fronts can be attractive as well as repulsive and dep ends strongly on their direction of propagation. Thus, the concentrati on mode leads to a new localization mechanism, which does not require any dispersion in contrast to that operating in the nonlinear Schrodin ger equation. Based on this mechanism alone, pairs of fronts in binary -mixture convection are expected to form stable pulses if they travel backward, i.e. opposite to the phase velocity. For positive velocities the interaction becomes attractive and destabilizes the pulses. These results are in qualitative agreement with recent experiments. Since t he new mechanism is very robust it is expected to be relevant in other systems as well in which a wave is coupled to a mean field.