TY  - JOUR
PB  - SciPost Foundation
DO  - 10.21468/SciPostPhys.20.1.025
TI  - Theory-agnostic searches for non-gravitational modes in black hole ringdown
PY  - 2026/01/30
UR  - https://scipost.org/SciPostPhys.20.1.025
JF  - SciPost Physics
JA  - SciPost Phys.
VL  - 20
IS  - 1
SP  - 025
A1  - Crescimbeni, Francesco
AU  - Jimenez Forteza, Xisco
AU  - Bhagwat, Swetha
AU  - Westerweck, Julian
AU  - Pani, Paolo
AB  - In any extension of General Relativity (GR), extra fundamental degrees of freedom couple to gravity. Besides deforming GR forecasts in a theory-dependent way, this coupling generically introduces extra modes in the gravitational-wave signal. We propose a novel theory-agnostic test of gravity to search for these nongravitational modes in black hole merger ringdown signals. To leading order in the GR deviations, their frequencies and damping times match those of a test scalar or vector field in a Kerr background, with only amplitudes and phases as free parameters. By applying this test to GW150914, GW190521, and GW200129, we find no strong evidence for an extra mode; however, its inclusion modifies the inferred distribution of the remnant spin. This test will be applicable for future detectors, which will achieve signal-to-noise ratios higher than 100 (and as high as 1000 for space-based detectors such as LISA). Such sensitivity will allow measurement of these modes with amplitude ratios as low as 0.02 for ground-based detectors (and as low as 0.003 for LISA), relative to the fundamental mode, enabling stringent agnostic constraints or detection of scalar/vector modes.
ER  -

@Article{10.21468/SciPostPhys.20.1.025,
	title={{Theory-agnostic searches for non-gravitational modes in black hole ringdown}},
	author={Francesco Crescimbeni and Xisco Jimenez Forteza and Swetha Bhagwat and Julian Westerweck and Paolo Pani},
	journal={SciPost Phys.},
	volume={20},
	pages={025},
	year={2026},
	publisher={SciPost},
	doi={10.21468/SciPostPhys.20.1.025},
	url={https://scipost.org/10.21468/SciPostPhys.20.1.025},
}