A class of transformations on the Dirac Hamiltonian

J. F. Roux, Phan Van Loc

Mustapha Maamache

We introduce the Dirac Inverted Oscillator, a new exactly solvable relativistic quantum system obtained through a Hermitian modification of the generalized momentum operator in the Dirac equation. In contrast to the conventional Dirac oscillator, where the generalized momentum is intrinsically non-Hermitian while the Hamiltonian remains Hermitian, the present construction reverses these Hermiticity properties: the generalized momentum becomes Hermitian, whereas the corresponding Dirac Hamiltonian is intrinsically non-Hermitian. This inversion leads to a new class of relativistic Hamiltonians within the framework of non-Hermitian quantum mechanics. Starting from the stationary Dirac equation, we derive the corresponding second-order wave equation and establish the generalized symmetry properties of the model, including pseudo-Hermiticity and pseudo- symmetry. We then prove that the Dirac Inverted Oscillator is exactly related to the conventional Dirac oscillator through a Hermitian but non-unitary similarity transformation generated by a dilation operator. This transformation is bijective and invertible, mapping the original non-Hermitian relativistic problem onto an equivalent Hermitian Schrodinger eigenvalue problem while preserving its complete spectral structure. The transformed Hermitian problem is solved analytically, allowing the exact relativistic spectrum and the corresponding eigenfunctions of the original non-Hermitian Hamiltonian to be determined explicitly. The present work therefore establishes an exact correspondence between a non-Hermitian relativistic Dirac system and a Hermitian Schrodinger problem, providing a new exactly solvable model and illustrating the effectiveness of Hermitian non-unitary similarity transformations for constructing analytically solvable relativistic Hamiltonians beyond the conventional Hermitian framework.

Ulrich D. Jentschura, J H Noble

We show that care is required in formulating the nonrelativistic limit of generalized Dirac Hamiltonians which describe particles and antiparticles interacting with static electric and/or gravitational fields. The Dirac-Coulomb and the Dirac-Schwarzschild Hamiltonians, and the corrections to the Dirac equation in a non-inertial frame, according to general relativity, are used as example cases in order to investigate the unitarity of the standard and "chiral" approaches to the Foldy-Wouthuysen transformation, and spurious parity-breaking terms. Indeed, we find that parity-violating terms can be generated by unitary pseudo-scalar transformations ("chiral" Foldy-Wouthuysen transformations). Despite their interesting algebraic properties, we find that "chiral" Foldy-Wouthuysen transformations change fundamental symmetry properties of the Hamiltonian and do not conserve the physical interpretation of the operators. Supplementing the discussion, we calculate the leading terms in the Foldy-Wouthuysen transformation of the Dirac Hamiltonian with a scalar potential (of the (1/r)-form and of the confining radially symmetric linear form), and obtain compact expressions for the leading higher-order corrections to the Dirac Hamiltonian in a non-inertial rotating reference frame "Mashhoon term").

Ph. Droz-Vincent

張家倫

The classical Hamiltonian of a point charged particle with intrinsic spin, which is composed of the relativistic orbit Hamiltonian and the spin Hamiltonian. This spin Hamiltonian can be derived from the Thomas-Bargmann-Michel-Telegdi equation. In our thesis, we will prove that the classical Hamiltonian in which the gyromagnetic ratio equals 2 is in agreement with the low-energy limit of the Dirac equation, the relativistic quantum theory for a spin-1/2 charged particle. For this purpose, we apply the Foldy-Wouthuysen transformation to the Dirac Hamiltonian under the assumptions of the static and homogeneous electromagnetic fields. Furthermore, in order to maintain such a correspondence in arbitrary gyromagnetic ratio cases, we perform the F-W transformation to the Dirac-Pauli Hamiltonian, which is the Dirac Hamiltonian plus the anomalous magnetic dipole moment Hamiltonian. Up to the twelfth-order of F-W transformed Dirac and Dirac-Pauli Hamiltonian, the calculation results are in accord with the corresponding classical Hamiltonians.