Transition from pushed-to-pulled fronts in piecewise linear reaction-diffusion systems

The front dynamics in reaction-diffusion equations with a piecewise linear reaction term is studied. A transition from pushed-to-pulled fronts when they propagate into the unstable state is found using a variational principle. This transition occurs for a critical value of the discontinuity position in the reaction function. In particular, we study how the transition depends on the properties of the reaction term and on the delay time. Our results are in good agreement with the numerical solutions of the model.