arXiv subjects
Publications and source records attributed to R. Kretschmer.
In infinite-dimensional Hilbert spaces, the application of the concept of quasi-Hermiticity to the description of non-Hermitian Hamiltonians with real spectra may lead to problems related to the definition of the metric operator. We discuss these problems by examining some examples taken from the recent literature and propose a formulation that is free of these difficulties.
We investigate the quantum-mechanical interpretation of models with non-Hermitian Hamiltonians and real spectra. After describing a general framework to reformulate such models in terms of Hermitian Hamiltonians defined on the Hilbert space $L_2(-\infty,\infty)$, we discuss the significance of the algebra of physical observables.
We study the quantum-mechanical interpretation of models with non-Hermitian Hamiltonians and real spectra. We set up a general framework for the analysis of such systems in terms of Hermitian Hamiltonians defined in the usual Hilbert space $L_2(-\infty,\infty)$. Special emphasis is put on the correct definition of the algebra of physical observables. Within this scheme we consider various examples, including the model recently introduced by Cannata et al. and the model of Hatano and Nelson.
A general form of multi-channel Bethe-Salpeter equation is considered. In contradistinction to the hitherto applied approaches, our coupled system of equations leads to the simultaneous solutions for all relativistic four-point Green functions (elastic and inelastic) appearing in a given theory. A set of relations which may be helpful in approximate treatments is given. An example of extracting useful information from the equations is discussed: we consider the most general trilinear coupling of N different scalar fields and obtain - in the ladder approximation - closed expressions for the Regge trajectories and their couplings to different channels in the vicinity of l = -1. Sum rules and an example containing non-obvious symmetry are discussed.
The high-energy behaviour in a multi-channel system is investigated in the framework of collinear asymptotic dynamics for massive particles. We consider the most general trilinear coupling of N different scalar fields. We find Regge behaviour and obtain closed expressions for the Regge trajectories and couplings. The results are corraborated in the multi-channel Bethe-Salpeter approach. The scattering processes dominated by single Regge trajectories are explicitly given.
The dynamics of massive particles in the collinear high momentum regime is investigated. Methods hitherto exploiting large time asymptotic Hamiltonians in the Dirac picture for the treatment of infrared divergences are adapted to the collinear asymptotic dynamics. The essential role of time ordering of the dressing operators is brought out.