# Operator based approach to PT-symmetric problems on a wedge-shaped contour

## TL;DR

This paper studies a PT-symmetric differential equation on a complex contour, classifies its spectral properties using limit-point/limit-circle theory, and analyzes the associated operators' spectra.

## Contribution

It introduces an operator-based approach to PT-symmetric problems on complex contours and classifies their spectral behavior using a classical limit-point/limit-circle scheme.

## Key findings

- Classification of the problem using limit-point/limit-circle theory.
- Construction of operators for half-line and full-axis problems.
- Spectral analysis of the associated operators.

## Abstract

We consider a second-order differential equation $$ -y''(z)-(iz)^{N+2}y(z)=\lambda y(z), \quad z\in \Gamma $$ with an eigenvalue parameter $\lambda \in \mathbb{C}$. In $\mathcal{PT}$ quantum mechanics $z$ runs through a complex contour $\Gamma\subset \mathbb{C}$, which is in general not the real line nor a real half-line. Via a parametrization we map the problem back to the real line and obtain two differential equations on $[0,\infty)$ and on $(-\infty,0].$ They are coupled in zero by boundary conditions and their potentials are not real-valued. The main result is a classification of this problem along the well-known limit-point/ limit-circle scheme for complex potentials introduced by A.R.\ Sims 60 years ago. Moreover, we associate operators to the two half-line problems and to the full axis problem and study their spectra.