Heidelberg 2022 – scientific programme

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GR: Fachverband Gravitation und Relativitätstheorie

GR 5: Gravitational Waves

GR 5.4: Talk

Tuesday, March 22, 2022, 17:15–17:35, GR-H2

Scattering gravitational waves off effective spinning black holes — •Venkata Sai Saketh Muddu and Justin Vines — Max Planck institute for gravitational physics, Potsdam Science Park Am Mühlenberg 1 D-14476 Potsdam, Germany

The scattering of gravitational waves off a black hole contains valuable information characterizing the response of a black hole to an external gravitational field. We present a new method for computing scattering amplitudes for this process, using an effective worldline theory where the black hole is treated as a point particle equipped with multipole moments. These moments can be intrinsic or induced. The effective action couples the black hole’s moments to an external gravitational field via interaction terms, which contain unknown coefficients. We consider a plane wave impinging on the black hole and consider its response to the incoming wave. In the effective theory, this leads to a scattered wave produced by the black hole. Comparing the scattered wave to the incident wave gives us the amplitude. We solve for the amplitude iteratively in powers of spin (the Kerr ring radius). Comparing the amplitude from the effective theory to that obtained by solving the Teukolsky equation in a Kerr background can fix the unknown coefficients in the effective action. Using our amplitude as an effective “gravitational Compton amplitude” in a triangle unitarity cut, we can also compute contributions to the relativistic scattering amplitude and subsequently the radial action for black-hole–black-hole scattering.