Speaker
Description
The ringdown phase of compact-object mergers is a key target for precision tests of gravity with next-generation detectors such as the Einstein Telescope. Current analyses are based on quasinormal modes, whose theoretical interpretation is however limited by their sensitivity to perturbations and by ambiguities associated with their definition in time, which can affect their robustness as probes of fundamental physics.
We adopt a different perspective based on greybody factors, which describe the propagation and scattering of gravitational waves in curved spacetime. We have recently shown that these quantities are directly encoded in the frequency-domain structure of the ringdown signal through the black-hole Green’s function, providing a theoretically well-defined alternative to the standard mode decomposition.
Unlike quasinormal modes, greybody factors are defined at real frequencies and are intrinsically more stable under small deformations of the system. As a result, they offer a robust and physically transparent characterization of the signal, naturally suited for high-precision measurements.
Building on these results, we are developing a data-analysis framework, GREY-RING, to test General Relativity through greybody factors. This framework enables a direct comparison with observational data in the frequency domain and is designed to fully exploit the sensitivity of third-generation detectors, as the model already achieves an accuracy compatible with signal-to-noise ratios of order 100-1000.
In particular, the Einstein Telescope will enable a precise reconstruction of the frequency-domain ringdown spectrum, allowing for accurate measurements of the remnant mass and spin, as well as direct constraints on alternative theories of gravity. This opens a new avenue for testing General Relativity in the strong-field regime and for probing possible deviations from the classical black-hole paradigm.
Based on:
[1] R. F. Rosato, K. Destounis, and P. Pani, Phys. Rev. D
110, L121501 (2024), https://arxiv.org/pdf/2406.01692.
[2] https://arxiv.org/pdf/2603.20490
[3] forthcoming works