Sources and sinks in the vicinity of a weakly inverted instability

The dynamics of perturbations around sinks and sources of traveling waves (TW) is studied in the cubic-quintic Ginzburg-Landau equation from an analytical point of view. Perturbations generically propagate in a direction opposite to the TW. Thus, a sink of TW is a source of perturbations and vice versa. For small values of time we predict there is a lower bound for the group velocity. For large values of time we predict the asymptotic value of the group velocity of the wave packet. Both predictions are in good agreement with direct numerical simulations.