Singular measure as principal eigenfunction of some nonlocal operators

In this paper, we are interested in the spectral properties of the generalised principal eigenvalue of some nonlocal operator. That is, we look for the existence of some particular solution $(λ,ϕ)$ of a nonlocal operator. $\int_ØK(x,y)ϕ(y)\, dy +a(x)ϕ(x) =-λϕ(x),$ where $Ø\subset\R^n$ is an open bounded connected set, $K$ a nonnegative kernel and $a$ is continuous. We prove that for the generalised principal eigenvalue $λ_p:=\sup \{λ\in \R \, |\, \exists \, ϕ\in C(Ø), ϕ> 0 \;\text{so that}\; \oplbϕØ+ a(x)ϕ+ λϕ\le 0\}$ there exists always a solution $(μ, λ_p)$ of the problem in the space of signed measure. Moreover $μ$ a positive measure. When $μ$ is absolutely continuous with respect to the Lebesgue measure, $μ=ϕ_p(x)$ is called the principal eigenfunction associated to $λ_p$. In some simple cases, we exhibit some explicit singular measures that are solutions of the spectral problem.

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