Cryptogauge symmetry and cryptoghosts for crypto-Hermitian Hamiltonians

TL;DR

This paper explores crypto-Hermitian Hamiltonians with complex potentials, revealing their real spectra, gauge system structure, phase transitions, and the potential for unitarity despite ghost states.

Contribution

It introduces a gauge-theoretic approach to crypto-Hermitian Hamiltonians and analyzes spectral transformations and phase transitions in these systems.

Findings

Spectrum of mixed Hamiltonian undergoes phase transitions as coupling g varies.

Multiple nontrivial quantum problems can be formulated from classical gauge systems.

Ghost states appear but unitarity might still be maintained.

Abstract

We discuss the Hamiltonian H = p^2/2 - (ix)^{2n+1} and the mixed Hamiltonian H = (p^2 + x^2)/2 - g(ix)^{2n+1}, which are crypto-Hermitian in a sense that, in spite of apparent complexity of the potential, a quantum spectral problem can be formulated such that the spectrum is real. We note first that the corresponding classical Hamiltonian system can be treated as a gauge system, with imaginary part of the Hamiltonian playing the role of the first class constraint. We observe then that, on the basis of this classical problem, several different nontrivial quantum problems can be formulated. We formulate and solve some such problems. We find in particular that the spectrum of the mixed Hamiltonian undergoes in certain cases rather amazing transformation when the coupling g is sent to zero. There is an infinite set of phase transitions in g when a couple of eigenstates of H coalesce and disappear from the spectrum. When quantization is done in the most natural way such that gauge constraints are imposed on quantum states, the spectrum should not be positive definite, but must involve the negative energy states (ghosts). We speculate that, in spite of the appearance of ghost states, unitarity might still be preserved.