We present a study of virtual absorption modes (VAMs) in Schwarzschild–de Sitter (SdS) spacetime under semiopen boundary conditions, where the VAMs correspond to total transmission modes (TTMs) with the reflection amplitude being vanishing. Our numerical analysis reveals that as the reflectivity $|\mathcal{K}|$ decreases, the imaginary parts of VAM spectra systematically decrease, with each overtone exhibiting a critical reflectivity at which $\mathrm{Im}({\omega }_{\mathrm{VAM}})=0$. Using simulations based on spectral collocation methods, we demonstrate that excitation precisely at a VAM spectrum leads to a virtual absorption process. These results establish VAMs as the spectral signatures of virtual absorption processes for exotic compact objects (ECOs).

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• General relativity
• Gravitation
• Gravitational waves