Spectrum properties of mixed operators under the mixed boundary conditions

TL;DR

This paper investigates the spectral properties of a combined operator consisting of the classical Laplacian and fractional Laplacian under mixed boundary conditions in bounded domains.

Contribution

It characterizes the spectrum of the superposition of Laplace and fractional Laplace operators with mixed boundary conditions, extending classical spectral theory to fractional and mixed operators.

Findings

Spectrum characterized for the combined operator

Boundary conditions influence spectral properties

Results applicable to smooth bounded domains

Abstract

In this paper, we describe the spectrum properties of mixed operators, precisely the superposition of the classical Laplace operator and the fractional Laplace operator in the presence of mixed boundary conditions, that is \begin{equation} \label{1} \left\{\begin{split} \mathcal{L}u\: &= \lambda u,~~\text{in} ~\Omega, u&=0~~~~~\text{in} ~~{U^c}, \mathcal{N}_s(u)&=0 ~~~~~\text{in} ~~{\mathcal{N}}, \frac{\partial u}{\partial \nu}&=0 ~~~~~\text{in}~~ \partial \Omega \cap \overline{\mathcal{N}}, \end{split} \right.\tag{$P_\lambda$} \end{equation} where $U= (\Omega \cup {\mathcal{N}} \cup (\partial\Omega\cap\overline{\mathcal{N}}))$, $\Omega \subseteq \mathbb{R}^n$ is a non empty bounded open set with sufficiently smooth boundary $\partial\Omega$, say of class $C^1$, and $\mathcal{D}$, $\mathcal{N}$ are open subsets of $\mathbb{R}^n\setminus{\bar{\Omega }}$ such that $\overline{{\mathcal{D}} \cup {\mathcal{N}}}= \mathbb{R}^n\setminus{\Omega}$, $\mathcal{D} \cap {\mathcal{N}}= \emptyset $ and $\Omega\cup \mathcal{N}$ is a bounded set with sufficiently smooth boundary, $\lambda >0$ is a real parameter and $\mathcal{L}= -\Delta+(-\Delta)^{s},~ \text{for}~s \in (0, 1).$