Constraints on Kalb-Ramond Gravity from EHT Observations of Rotating Black Holes in Traceless Conformal Electrodynamics
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| Format: | Preprint |
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2025
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| author | Sekhmani, Yassine Boshkayev, Kuantay Azreg-Aïnou, Mustapha Maurya, Sunil K. Altanji, Mohamed Urazalina, Ainur |
| author_facet | Sekhmani, Yassine Boshkayev, Kuantay Azreg-Aïnou, Mustapha Maurya, Sunil K. Altanji, Mohamed Urazalina, Ainur |
| contents | We present a phenomenological study of rotating, charged black holes in Einstein gravity coupled to a traceless (conformal) matter sector formed by ModMax nonlinear electrodynamics and a Kalb-Ramond two-form that spontaneously breaks local Lorentz symmetry. Starting from a family of obtained static, Schwarzschild-like solutions with a traceless Kalb-Ramond sector, we construct the stationary, axisymmetric counterpart via the Newman-Janis algorithm. The resulting Newman-Kerr-like metric depends on four intrinsic parameters: the electric charge $Q$, the ModMax nonlinearity $γ$, the Lorentz-violation amplitude $\ell$ and the spin $a$. We analyze horizon structure and separatrices in parameter space, derive the null geodesic equations and obtain the photon capture boundary that defines the black hole shadow. Using ray-tracing, we compute shadow silhouettes and a suite of shadow observables (areal radius, characteristic radius $R_s$, distortion $δ$, oblateness $D$) and show how $γ$ and $\ell$ produce qualitatively distinct effects: $γ$ acts as a screening factor for the electromagnetic imprint, while $\ell$ introduces angular-dependent metric rescalings that deform shadow shape beyond simple size rescaling. We confront model predictions with EHT angular-radius measurements for M87$^*$ and Sgr A$^*$ and derive conservative bounds on the combinations of $(Q,γ,\ell,a)$. Our results identify an effective charge combination $Q_{\rm eff}\simeq e^{-γ}Q^{2}/(1-\ell)^{2}$ and demonstrate that modest $Q_{\rm eff}$ remains compatible with current EHT images while large $Q_{\rm eff}$ is progressively disfavored. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2509_16782 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Constraints on Kalb-Ramond Gravity from EHT Observations of Rotating Black Holes in Traceless Conformal Electrodynamics Sekhmani, Yassine Boshkayev, Kuantay Azreg-Aïnou, Mustapha Maurya, Sunil K. Altanji, Mohamed Urazalina, Ainur General Relativity and Quantum Cosmology High Energy Astrophysical Phenomena We present a phenomenological study of rotating, charged black holes in Einstein gravity coupled to a traceless (conformal) matter sector formed by ModMax nonlinear electrodynamics and a Kalb-Ramond two-form that spontaneously breaks local Lorentz symmetry. Starting from a family of obtained static, Schwarzschild-like solutions with a traceless Kalb-Ramond sector, we construct the stationary, axisymmetric counterpart via the Newman-Janis algorithm. The resulting Newman-Kerr-like metric depends on four intrinsic parameters: the electric charge $Q$, the ModMax nonlinearity $γ$, the Lorentz-violation amplitude $\ell$ and the spin $a$. We analyze horizon structure and separatrices in parameter space, derive the null geodesic equations and obtain the photon capture boundary that defines the black hole shadow. Using ray-tracing, we compute shadow silhouettes and a suite of shadow observables (areal radius, characteristic radius $R_s$, distortion $δ$, oblateness $D$) and show how $γ$ and $\ell$ produce qualitatively distinct effects: $γ$ acts as a screening factor for the electromagnetic imprint, while $\ell$ introduces angular-dependent metric rescalings that deform shadow shape beyond simple size rescaling. We confront model predictions with EHT angular-radius measurements for M87$^*$ and Sgr A$^*$ and derive conservative bounds on the combinations of $(Q,γ,\ell,a)$. Our results identify an effective charge combination $Q_{\rm eff}\simeq e^{-γ}Q^{2}/(1-\ell)^{2}$ and demonstrate that modest $Q_{\rm eff}$ remains compatible with current EHT images while large $Q_{\rm eff}$ is progressively disfavored. |
| title | Constraints on Kalb-Ramond Gravity from EHT Observations of Rotating Black Holes in Traceless Conformal Electrodynamics |
| topic | General Relativity and Quantum Cosmology High Energy Astrophysical Phenomena |
| url | https://arxiv.org/abs/2509.16782 |