Photon rings, gravitational lensing, and ISCOs of exotic compact objects in Einstein-scalar-Maxwell theories
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arXiv
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| Natura: | Preprint |
| Pubblicazione: |
2026
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| author | De Felice, Antonio Tsujikawa, Shinji |
| author_facet | De Felice, Antonio Tsujikawa, Shinji |
| contents | In Einstein-scalar-Maxwell theories with a coupling between the scalar field $ϕ$ and the electromagnetic field strength $F$ of the form $μ(ϕ) F$, we investigate the existence of exotic compact objects (ECOs) and their observational signatures in photon and massive-particle dynamics. For $μ(ϕ)$ diverging at the origin while all physical quantities remain finite, we demonstrate the existence of electrically charged ECOs with a shell-like structure whose density peaks at an intermediate radius. We compute their mass and radius, together with the scalar and vector field profiles, on a static and spherically symmetric background. We then examine the existence of photon rings and place bounds on a model parameter by requiring the absence of a linearly stable photon ring. Under this condition, photon echoes from ECOs are absent. We also compute the gravitational-lensing deflection angle $Ψ$ and show that it attains a maximum for an impact parameter of the same order as the ECO radius. Finally, we study the parameter space in which innermost stable circular orbits of massive particles exist. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2602_23657 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Photon rings, gravitational lensing, and ISCOs of exotic compact objects in Einstein-scalar-Maxwell theories De Felice, Antonio Tsujikawa, Shinji General Relativity and Quantum Cosmology Cosmology and Nongalactic Astrophysics High Energy Physics - Theory In Einstein-scalar-Maxwell theories with a coupling between the scalar field $ϕ$ and the electromagnetic field strength $F$ of the form $μ(ϕ) F$, we investigate the existence of exotic compact objects (ECOs) and their observational signatures in photon and massive-particle dynamics. For $μ(ϕ)$ diverging at the origin while all physical quantities remain finite, we demonstrate the existence of electrically charged ECOs with a shell-like structure whose density peaks at an intermediate radius. We compute their mass and radius, together with the scalar and vector field profiles, on a static and spherically symmetric background. We then examine the existence of photon rings and place bounds on a model parameter by requiring the absence of a linearly stable photon ring. Under this condition, photon echoes from ECOs are absent. We also compute the gravitational-lensing deflection angle $Ψ$ and show that it attains a maximum for an impact parameter of the same order as the ECO radius. Finally, we study the parameter space in which innermost stable circular orbits of massive particles exist. |
| title | Photon rings, gravitational lensing, and ISCOs of exotic compact objects in Einstein-scalar-Maxwell theories |
| topic | General Relativity and Quantum Cosmology Cosmology and Nongalactic Astrophysics High Energy Physics - Theory |
| url | https://arxiv.org/abs/2602.23657 |