We present new results for classical-particle propagation subject to Lorentz violation. Our analysis is dedicated to spin-nondegenerate operators of arbitrary mass dimension provided by the fermion sector of the Standard-Model extension. In particular, classical Lagrangians are obtained for the operators ${\widehat{b}}_{\mu }$ and ${\widehat{H}}_{\mu \nu }$ as perturbative expansions in Lorentz violation. The functional dependence of the higher-order contributions in the background fields is found to be quite peculiar, which is probably attributed to particle spin playing an essential role for these cases. This paper closes one of the last gaps in understanding classical-particle propagation in the presence of Lorentz violation. Lagrangians of the kind presented will turn out to be valuable for describing particle propagation in curved backgrounds with diffeomorphism invariance and/or local Lorentz symmetry explicitly violated.

• Received 27 March 2021
• Accepted 5 April 2021

DOI:https://doi.org/10.1103/PhysRevD.103.095029

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Published by the American Physical Society