This analysis derives relations for circular photon orbits in static spacetimes, suggesting Finsler metrics reveal new dynamics.
We consider static spacetimes in spherical coordinates whose angular sector is described by a Finsler metric rather than the standard round metric on S². Our first contribution is kinematical: keeping the lapse and radial factors eν(r), eϑ(r) arbitrary and using only Killing symmetries and the null constraint, we derive model--independent relations for circular photon orbits and the effective dynamics. Specializing the Finsler metric to a positive constant flag curvature Randers sphere we derive exact expressions for the conserved angular charge and the critical impact parameter, and we quantify a Finslerian Sagnac--type effect. Our second contribution is dynamical: we consider the field equations used in the literature to fix (e^ν,eϑ). We revisit the hairy black hole family in a recent paper by Nekouee et al. demonstrating that the equatorial restriction employed in such a work eliminates the genuinely Finslerian features and showing that the claimed new solutions reproduce previously known results obtained by Ovalle et al.
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Erasmo Caponio (2025) studied this question.
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