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arXiv · 2607.26141

Light propagation and intensity transport in metric-affine geometry

Antonio De Felice·Lavinia Heisenberg·Gonzalo J. Olmo·Carlos Pastor-Marcos
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Abstract

We study electromagnetic wave propagation in metric--affine geometries, where torsion and non-metricity may be present and the coupling between electromagnetism and spacetime is no longer unique. Rather than choosing a particular coupling prescription a priori, we construct electromagnetic sectors that preserve standard $U(1)$ gauge invariance and projective invariance of the affine connection as guiding symmetry principles. We introduce two representative models, one in which the Maxwell term is dressed by a scalar prefactor built from non-Riemannian invariants, and another in which the kinetic term is modified by a rank--four constitutive tensor acting as an anisotropic medium. We derive their geometric--optics limits and show that their couplings can modify the effective light cone, change the relation between field amplitude and intensity, induce polarization-dependent propagation, and generate birefringence and mode mixing. These results thus provide the formal basis for a broader phenomenological study connecting torsion and non-metricity with electromagnetic observables in concrete metric--affine backgrounds, including black-hole imaging, birefringent lensing, polarization observables, and departures from photon-number conservation.

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Antonio De Felice, Lavinia Heisenberg, Gonzalo J. Olmo, Carlos Pastor-Marcos. 2026-07-28. Light propagation and intensity transport in metric-affine geometry. https://arxiv.org/abs/2607.26141

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