The spectrum of a Harmonic Oscillator Operator Perturbed by Point Interactions

TL;DR

This paper analyzes the spectrum of a harmonic oscillator operator perturbed by point interactions, deriving asymptotic formulas for eigenvalues and conditions for non-real eigenvalues, extending to general two-point interactions.

Contribution

It provides explicit asymptotic eigenvalue formulas and bounds for non-real eigenvalues for harmonic oscillator operators with point interactions, including complex perturbations.

Findings

Eigenvalues are asymptotically simple and follow a specific formula involving sine functions.

Number of non-real eigenvalues is finite and bounded by a logarithmic function of the perturbation parameter.

Results extend to general two-point delta interactions with complex coefficients.

Abstract

We consider the operator $ L = - (d/dx)^2 + x^2 y + w(x) y , y \in L^2(\mathbb{R}) $, where $ w(x) = s [ \delta(x - b) - \delta(x + b)], b \neq 0,$ real, $s \in \mathbb{C}$. This operator has a discrete spectrum: eventually the eigenvalues are simple and $\lambda_n = (2n + 1) + s^2 (\kappa(n) / n) + \rho(n)$, where $ \kappa(n) = \frac{1}{2\pi} [(-1)^{n + 1} \sin ( 2 b \sqrt{2n} ) - \frac{1}{2} \sin ( 4 b \sqrt{2n} ) ]$ and $ |\rho(n) | \leq C (\log n) / (n^{3/2})$ If $s = i \gamma$, $\gamma$ real, the number $T(\gamma)$ of non-real eigenvalues is finite, and $T(\gamma) \leq [ C (1 + | \gamma |) \log (e + | \gamma |)]^2.$ The analogue of the above equations is given in the case of any two-point interaction perturbation $w(x) = c_+ \delta(x - b) + c_- \delta(x + b), c_+, c_- \in \mathbb{C}. $