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| Natura: | Preprint |
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2025
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| Accesso online: | https://arxiv.org/abs/2512.14773 |
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| _version_ | 1866915680560873472 |
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| author | Ökten, M. Baran |
| author_facet | Ökten, M. Baran |
| contents | We compute the achromatic gravitational imprint that Kerr spacetime leaves on linear polarization at the photon ring. Recasting parallel transport in a null Frenet--Serret frame yields a single scalar evolution law for the electric-vector position angle. On the observer's screen, the Kerr-minus-Schwarzschild pattern on the direct critical curve is nonzero, strictly odd under spin reversal after a half-turn azimuth relabelling, and tightly confined to a thin annulus. Using backward-shot, Carter-separated geodesics with midpoint RK2 transport, we achieve second-order convergence and degree-scale amplitudes that grow monotonically with spin and inclination (RMS $\simeq 0.5$--$2^\circ$ for $a/M\gtrsim 0.8$, $i\gtrsim 60^\circ$). Three independent constructions -- Frenet--Serret line integral, explicit Levi--Civita transport of the polarization vector, and the phase of the Walker--Penrose constant -- agree ray by ray. We then define a parity-odd ring estimator that is intrinsically achromatic after standard wavelength-squared regression, symmetry-protected against common even-parity systematics, and compressed into low azimuthal modes. This yields a minimal two-parameter template (spin and inclination) for mm/sub-mm polarimetry of horizon-scale rings in sources such as M87$^\ast$ and Sgr~A$^\ast$. The pipeline enables either a detection of the strong-field parallel-transport phase induced by frame dragging or informative upper limits. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2512_14773 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Achromatic, spin-odd Kerr EVPA as a null Frenet--Serret torsion integral on the photon ring Ökten, M. Baran General Relativity and Quantum Cosmology Astrophysics of Galaxies High Energy Astrophysical Phenomena We compute the achromatic gravitational imprint that Kerr spacetime leaves on linear polarization at the photon ring. Recasting parallel transport in a null Frenet--Serret frame yields a single scalar evolution law for the electric-vector position angle. On the observer's screen, the Kerr-minus-Schwarzschild pattern on the direct critical curve is nonzero, strictly odd under spin reversal after a half-turn azimuth relabelling, and tightly confined to a thin annulus. Using backward-shot, Carter-separated geodesics with midpoint RK2 transport, we achieve second-order convergence and degree-scale amplitudes that grow monotonically with spin and inclination (RMS $\simeq 0.5$--$2^\circ$ for $a/M\gtrsim 0.8$, $i\gtrsim 60^\circ$). Three independent constructions -- Frenet--Serret line integral, explicit Levi--Civita transport of the polarization vector, and the phase of the Walker--Penrose constant -- agree ray by ray. We then define a parity-odd ring estimator that is intrinsically achromatic after standard wavelength-squared regression, symmetry-protected against common even-parity systematics, and compressed into low azimuthal modes. This yields a minimal two-parameter template (spin and inclination) for mm/sub-mm polarimetry of horizon-scale rings in sources such as M87$^\ast$ and Sgr~A$^\ast$. The pipeline enables either a detection of the strong-field parallel-transport phase induced by frame dragging or informative upper limits. |
| title | Achromatic, spin-odd Kerr EVPA as a null Frenet--Serret torsion integral on the photon ring |
| topic | General Relativity and Quantum Cosmology Astrophysics of Galaxies High Energy Astrophysical Phenomena |
| url | https://arxiv.org/abs/2512.14773 |