Asymptotic Behavior for a nonlocal diffusion equation on the half line

Abstract

We study the large time behavior of solutions to a non-local diffusion equation, $u_t=J*u-u$ with $J$ smooth, radially symmetric and compactly supported, posed in $\mathbb{R}_+$ with zero Dirichlet boundary conditions. In sets of the form $x\ge \xi t^{1/2}$, $\xi>0$, the outer region, the asymptotic behavior is given by a multiple of the dipole solution for the local heat equation, and the solution is $O(t^{-1})$. The proportionality constant is determined from a conservation law, related to the asymptotic first momentum. On compact sets, the inner region, after scaling the solution by a factor $t^{3/2}$, it converges to a multiple of the unique stationary solution of the problem that behaves as $x$ at infinity. The precise proportionality factor is obtained through a matching procedure with the outer behavior. Since the outer and the inner region do not overlap, the matching is quite involved. It has to be done for the scaled function $t^{3/2}u(x,t)/x$, which takes into account that different scales lead to different decay rates.