On finitely many resonances emerging under distant perturbations in multi-dimensional cylinders

TL;DR

This paper studies how finitely many resonances emerge near a specific spectral point in multi-dimensional cylinders with distant perturbations, showing they are exponentially small and analyzing their asymptotics.

Contribution

It demonstrates the existence of finitely many resonances under certain spectral conditions and derives their leading asymptotic terms, advancing understanding of spectral effects of distant perturbations.

Findings

Finitely many resonances occur near  under specified conditions.

Resonance asymptotics are exponentially small.

The assumption is conjectured to be necessary for finiteness of resonances.

Abstract

We consider a general elliptic operator in an infinite multi-dimensional cylinder with several distant perturbations; this operator is obtained by ``gluing'' several single perturbation operators $\mathcal{H}^{(k)}$, $k=1,\ldots,n$, at large distances. The coefficients of each operator $\mathcal{H}^{(k)}$ are periodic in the outlets of the cylinder; the structure of these periodic parts at different outlets can be different. We consider a point $\lambda_0 \in\mathds{R}$ in the essential spectrum of the operator with several distant perturbations and assume that this point is not in the essential spectra of middle operators $\mathcal{H}^{(k)}$, $k=2,\ldots,n-1$, but is an eigenvalue of at least one of $\mathcal{H}^{(k)}$, $k=1,\ldots,n$. Under such assumption we show that the operator with several distant perturbations possesses finitely many resonances in the vicinity of $\lambda_0$. We find the leading terms in asymptotics for these resonances, which turn out to be exponentially small. We also conjecture that the made assumption selects the only case, when the distant perturbations produce finitely many resonances in the vicinity of $\lambda_0$. Namely, as $\lambda_0$ is in the essential spectrum of at least one of operators $\mathcal{H}^{(k)}$, $k=2,\ldots,n-1$, we do expect that infinitely many resonances emerge in the vicinity of $\lambda_0$.