Question

Is zitterbewegung physical or not?

Answer 1

It appears that zitterbewegung, a frequency associated with the total energy of a particle or system, is widely considered to be an unphysical quantity (e.g., Kobakhidze et.al.), @Lubos Motl, McMillan). However, a few physicists including Hestenes, Recami et.al.,consider it to be a fundamental, physical quantity.

It appears that, for example, the photon emitted in transitions between two states in an atom has precisely the frequency of the "beat frequency" (difference frequency) between the zitterbewegung frequencies of the two states.

Why is zitterbewegung considered unphysical by most physicists, and has there been a solid refutation of Hestenes' position that zitterbewegung is physical?

You appear to be misreading several of your sources and slapping an ill-defined "unphysical" label on selected statements in them. Zitterbewegung is needless in QFT, but topical and useful in Dirac's equivalent relativistic fermion QM and results in specific terms in the correct hamiltonian, so, then "physical". At least one source indicates it is merely obsolete, as you may bypass it in QFT, not "unphysical". –

Answer 2

$\textbf {\huge{ \red {ANSWER }}}$

This sort of gives the impression that we don't know whether zitterbewegung is real or not. It's true that it's never been observed directly, as motion, but its physical effects are easy.