Characterization of the constant sign of a class of Periodic and Neumann Green’s functions via spectral theory

Abstract

In this paper we characterize the regions of constant sign of the Green's fucntions related to operator $T_n[p,M]\,u(t)=u^{(n)}(t)+p\,u^{(n-2)}(t)+M\,u(t)$, with $n$ an even number, $n\ge 4$, and $p\le 0$, coupled to periodic or Neumann boundary conditions. The results generalize the situation considered in \cite{CabSom_Eloe} for the particular case of $p=0$.