Gauge invariance and the dirac equation |
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Authors: | Donald H Kobe |
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Institution: | (1) Department of Physics, North Texas State University, 76203 Denton, Texas |
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Abstract: | The gauge invariance of the Dirac equation is reviewed and gauge-invariant operators are defined. The Hamiltonian is shown
to be gauge dependent, and an energy operator is defined which is gauge invariant. Gauge-invariant operators corresponding
to observables are shown to satisfy generalized Ehrenfest theorems. The time rate of change of the expectation value of the
energy operator is equal to the expectation value of the power operator. The virial theorem is proved for a relativistic electron
in a time-varying electromagnetic field. The conventional approach to probability amplitudes, using the eigenstates of the
unperturbed Hamiltonian, is shown in general to be gauge dependent. A gaugeinvariant procedure for probability amplitudes
is given, in which eigenstates of the energy operator are used. The two methods are compared by applying them to an electron
in a zero electromagnetic field in an arbitrary gauge.
Presented at the Dirac Symposium, Loyola University, New Orleans, May 1981. |
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