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arXiv · 2606.18470

Exact propagating Dirac wave packets in an attractive Coulomb-like potential

Siddhant Das
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Abstract

We construct exact, positive-energy, normalizable wave-packet solutions of the Dirac equation in the axisymmetric potential $V=-\,v_0/\rho$ -- to our knowledge, the first such solutions in any external potential. Remarkably, one family comprises only elementary functions whose longitudinal profiles reproduce the free-Schr\"odinger Hermite--Gauss wave packets in the nonrelativistic limit. All packets share two striking features: (i) a probability density that is pointwise decoupled from spin orientation -- despite the inherent spin-orbit coupling of the Dirac equation -- and (ii) a complete freezing of their time evolution at the critical coupling $v_0\to\hbar c/2$. We also present a simple scheme that maps solutions of the 2D Helmholtz equation to further exact Dirac wave packets.

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Siddhant Das. 2026-06-16. Exact propagating Dirac wave packets in an attractive Coulomb-like potential. https://arxiv.org/abs/2606.18470

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