Spectral asymptotics for the third order operator with periodic coefficients

TL;DR

This paper analyzes the spectral properties of a third order periodic differential operator, deriving asymptotics of eigenvalues and spectrum multiplicities, especially for small coefficients, revealing detailed spectral structure at high energies.

Contribution

It provides the first detailed high energy asymptotics for eigenvalues and spectral multiplicities of a third order periodic operator, including small coefficient cases.

Findings

Spectrum is absolutely continuous and covers the real line.

Eigenvalue asymptotics are determined at high energies.

Spectrum multiplicity behavior is characterized for small coefficients.

Abstract

We consider the self-adjoint third order operator with 1-periodic coefficients on the real line. The spectrum of the operator is absolutely continuous and covers the real line. We determine the high energy asymptotics of the periodic, anti-periodic eigenvalues and of the branch points of the Lyapunov function. Furthermore, in the case of small coefficients we show that either whole spectrum has multiplicity one or the spectrum has multiplicity one except for a small spectral nonempty interval with multiplicity three. In the last case the asymptotics of this small interval is determined.