For a spin-1/2 particle moving in a background magnetic field in noncommutative phase space, Dirac equation is solved when the particle is allowed to move off the plane that the magnetic field is perpendicular to. It is shown that the motion of the charged particle along the magnetic field has the effect to increase the magnetic field. In the classical limit, matrix elements of the velocity operator related to the probability give a clear physical picture: Along an effective magnetic field the mechanical momentum is conserved and the motion perpendicular to the effective magnetic field follows a round orbit. If using the velocity operator defined by the coordinate operators, the motion becomes complicated. Key words: non-commutative phase space,Dirac equation,velocity operator,magnetic field PACS: 02.40.Gh,03.65.-w,11.10.Nx
IntroductionTo resolve the problem of infinite energies in quantum field theory, the idea of space-time non-commutativity was proposed [1]. Discoveries in string theory and M-theory that effects of noncommutative(NC) spaces may appear near the string scale and at higher energies [2-4] greatly motivate the studies in these areas. Recently, a lot of problems have been investigated on the theory of NC spaces such as the quantum Hall effects [5][6][7][8][9], the harmonic oscillator [10][11][12][13][14], the coherent states [15], the thermodynamics [16], the classical-quantum relationship [17], the motion of the spin-1/2 particle under a uniform magnetic field [18], various kinds of relativistic oscillators [19, 20,23,24], etc. In [18], the particle is confined to the plane the applied magnetic field is perpendicular to. Here in this article, we discuss the case that the particle is allowed to move off the plane.In the next section, we derive the energy spectrum and wave functions in 3D NC phase space. It is shown that the NC 3D phase space induces an effective magnetic field in a new direction. Matrix elements of velocity and momentum operators give solutions to the semiclassical equations of motion. The final section is the summary.