Horizon-absorption effects in coalescing black-hole binaries: An effective-one-body study of the nonspinning case

We study the horizon absorption of gravitational waves in coalescing, circularized, nonspinning black-hole binaries. The horizon-absorbed fluxes of a binary with a large mass ratio (q = 1000) obtained by numerical perturbative simulations are compared with an analytical, effective-one-body (EOB) resummed expression recently proposed. The perturbative method employs an analytical, linear in the mass ratio, EOB-resummed radiation reaction, and the Regge-Wheeler-Zerilli formalism for wave extraction. Hyperboloidal layers are employed for the numerical solution of the Regge-Wheeler-Zerilli equations to accurately compute horizon fluxes up to the late plunge phase. The horizon fluxes from perturbative simulations and the EOB-resummed expression agree at the level of a few percent down to the late plunge. An upgrade of the EOB model for nonspinning binaries that includes horizon absorption of angular momentum as an additional term in the resummed radiation reaction is then discussed. The effect of this term on the waveform phasing for binaries with mass ratios spanning 1–1000 is investigated. We confirm that for comparable and intermediate-mass-ratio binaries horizon absorption is practically negligible for detection with advanced LIGO and the Einstein Telescope (faithfulness ≥ 0.997).