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General Relativity and Quantum Cosmology, gr-qc
Abstract:
We probe the gravitational interaction of two black holes in the strong-field
regime by computing the scattering angle $\chi$ of hyperbolic-like, close
binary-black-hole encounters as a function of the impact parameter. The fully
general-relativistic result from numerical relativity is compared to two
analytic approximations: post-Newtonian theory and the effective-one-body
formalism. As the impact parameter decreases, so that black holes pass within a
few times their Schwarzschild radii, we find that the post-Newtonian prediction
becomes quite inaccurate, while the effective-one-body one keeps showing a good
agreement with numerical results. Because we have explored a regime which is
very different from the one considered so far with binaries in quasi-circular
orbits, our results open a new avenue to improve analytic representations of
the general-relativistic two-body Hamiltonian.