Geometrized effective-one-body formalism for extreme-mass-ratio limits: Generic orbits

TL;DR

This paper develops an analytical effective-one-body framework for modeling generic, three-dimensional orbits of compact objects around supermassive Kerr black holes, incorporating mass-ratio effects to improve gravitational waveform templates.

Contribution

It introduces an analytical method to compute trajectories and orbital frequencies for generic orbits with mass-ratio corrections within the EOB formalism.

Findings

Derived explicit formulas for orbital trajectories and frequencies.

Constructed an approximate Carter constant for generic orbits.

Provided a foundation for more accurate gravitational waveform modeling.

Abstract

Compact objects inspiraling into supermassive black holes, known as extreme-mass-ratio inspirals, are an important source for future space-borne gravitational-wave detectors. When constructing waveform templates, usually the adiabatic approximation is employed to treat the compact object as a test particle for a short duration, and the radiation reaction is reflected in the changes of the constants of motion. However, the mass of the compact object should have contributions to the background. In the present paper, employing the effective-one-body formalism, we analytically calculate the trajectories of a compact object around a massive Kerr black hole with generally three-dimensional orbits and express the fundamental orbital frequencies in explicit forms. In addition, by constructing an approximate "constant" similar to the Carter constant, we transfer the dynamical quantities such as energy, angular momentum, and the "Carter constant" to the semilatus rectum, eccentricity, and orbital inclination with mass-ratio corrections. The linear mass-ratio terms in the formalism may not be sufficient for accurate waveforms, but our analytical method for solving the equations of motion could be useful in various approaches to building waveform models.