Rates of acceleration in semilinear integro-differential equations with (very) weak Allee effects

This talk is devoted to studying propagation phenomena in reaction diffusion and integro-differential equations with a weakly degenerate non-linearity. The reaction terms cover the standard weak Allee effect one and an intermediate between the classical logistic (or Fisher-KPP) non-linearity and the standard weak Allee effect one. We study the effect of the tails of the dispersal kernel on the rate of expansion. When the tail of the kernel is sub-exponential, the exact separation between existence and nonexistence of travelling waves is exhibited. This, in turn, provides the exact separation between finite speed propagation and acceleration in the Cauchy problem. Moreover, the exact rates of acceleration for dispersal kernels with sub-exponential and algebraic tails are provided. Our approach is generic and covers a large variety of dispersal kernels including those leading to convolution and fractional Laplace operators. Numerical simulations are provided to illustrate our results. This comes from joint works with Jérôme Coville, Guillaume Legendre, and Xi Zhang.