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Europhysics Letters (EPL)

Solution of the generalized Dirac equation in a time-dependent linear potential: Relativistic geometric amplitude factor

Mustapha Maamache, Halim Lakehal

Published Aug 25, 2004• 13 citations
Publisher

Abstract

We present exact solutions of the Dirac equation for a particle with time-dependent mass moving in a time-dependent linear potential. In addition, we show that the time evolution can be described in terms of classical concept which leads to solve this problem by standard techniques of Hamiltonian mechanics. Geometric amplitude emerges as an adiabatic limit of the exact dynamics.

DOI
10.1209/epl/i2004-10109-6

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We present exact solutions of the Dirac equation for a particle with time-dependent mass moving in a time-dependent linear potential. In addition, we show that the time evolution can be described in terms of classical concept which leads to solve this problem by standard techniques of Hamiltonian mechanics. Geometric amplitude emerges as an adiabatic limit of the exact dynamics.
We study a relativistic charged Dirac particle moving in a rotating magnetic field. By using a time-dependent unitary transformation, the Dirac equation with the time-dependent Hamiltonian can be reduced to a Dirac-like equation with a time-independent effective Hamiltonian. Eigenstates of the effective Hamiltonian correspond to cyclic solutions of the original Dirac equation. The nonadiabatic geometric phase of a cyclic solution can be expressed in terms of the expectation value of the component of the total angular momentum along the rotating axis, regardless of whether the solution is explictly available. For a slowly rotating magnetic field, the eigenvalue problem of the effective Hamiltonian is solved approximately and the geometric phases are calculated. The same problem for a charged or neutral Dirac particle with an anomalous magnetic moment is discussed briefly.
A relativistically invariant representation of the generalized momentum of a particle in an external field is proposed. In this representation, the dependence of the potentials of the interaction of the particle with the field on the particle velocity is taken into account. The exact correspondence of the expressions of energy and potential energy for the classical Hamiltonian is established, which makes identical the solutions to the problems of mechanics with relativistic and nonrelativistic approaches. The invariance of the proposed representation of the generalized momentum makes it possible to equivalently describe a physical system in geometrically conjugate spaces of kinematic and dynamic variables. Relativistic invariant equations are proposed for the action function and the wave function based on the invariance of the representation of the generalized momentum. The equations have solutions for any values of the constant interaction of the particle with the field, for example, in the problem of a hydrogen-like atom, when the atomic number of the nucleus is Z > 137. Based on the parametric representation of the action, the expression for the canonical Lagrangian, the equations of motion, and the expression for the force acting on the charge are derived when moving in an external electromagnetic field. The Dirac equation with the correct inclusion of the interaction for a particle in an external field is presented. In this form, the solutions of the equations are not limited by the value of the interaction constant. The solutions of the problem of charge motion in a constant electric field, the problems for a particle in a potential well and the passage of a particle through a potential barrier, the problems of motion in an exponential field (Morse), and also the problems of a hydrogen atom are given.
We study a relativistic charged Dirac particle moving in a rotating magnetic field. By using a time-dependent unitary transformation, the Dirac equation with the time-dependent Hamiltonian can be reduced to a Dirac-like equation with a time-independent effective Hamiltonian. Eigenstates of the effective Hamiltonian correspond to cyclic solutions of the original Dirac equation. The nonadiabatic geometric phase of a cyclic solution can be expressed in terms of the expectation value of the component of the total angular momentum along the rotating axis, regardless of whether the solution is explictly available. For a slowly rotating magnetic field, the eigenvalue problem of the effective Hamiltonian is solved approximately and the geometric phases are calculated. The same problem for a charged or neutral Dirac particle with an anomalous magnetic moment is discussed briefly.
The purpose of this paper is to develop a single solution to both the Klein-Gordon & Dirac equations that expresses both the QM and the classical aspects of particles. It is found that this can be done, but only in the context of a system that has an initial event (T = 0) and is expanding at c, thus it is consistent with a big bang representation of the universe. The equations are defined in geometric algebraic, and the KGD equation will be considered a single equation factorable into linear products of the two linear Dirac expressions, with a solution defined analogously to path integrals. The solution has botha Gaussian shaped amplitude, (classical), and phase, (QM) components satisfying the quadratic KG equation, and the linear Dirac expression. The equation differentials are not restricted to representing the normal QM operator replacement of p and E, applicable to the linear equation, but have a broader context in operating on the more complex function with amplitude and phase factors. The solutions represent the particle at a single event, thus the standard view of the solution being a probability amplitude field over spacetime is not applicable, but an alternate observational field is illustrated that demonstrates the connection of the solutions to the observed wave characteristics. The phase factors are as usual cyclic, but the amplitude factors exist only in the context of the entire interval. The amplitude factor of the solution is proportional to mass and thus should offer insight into particle mass ratios.