The Bramson delay in the non-local Fisher-KPP equation
Résumé
We consider the non-local Fisher-KPP equation modeling a population with individuals competing with each other for
resources with a strength related to their distance, and obtain the asymptotics for the position of the
invasion front starting from a localized population. Depending on the behavior of the competition kernel at infinity, the location of the front is
either $2t - ({3}/2)\log t + O(1)$, as in the local case, or $2t - O(t^\beta)$ for some explicit $\beta \in (0,1)$. Our main tools here are a
local-in-time Harnack inequality and an analysis of the linearized problem with a suitable moving Dirichlet boundary condition. Our analysis also yields, for any $\beta\in(0,1)$, examples of Fisher-KPP type non-linearities $f_\beta$ such that the front for the local
Fisher-KPP equation with reaction term $f_\beta$ is at $2t - O(t^\beta)$.
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