GWhyb · Hybrid models of extreme-mass-ratio inspirals for precision gravitational wave astronomy

With the Laser Interferometer Space Antenna (LISA) due for launch in 2035, sources of gravitational waves in the millihertz frequency band are garnering significant attention. Of special interest are extreme-mass-ratio inspirals (EMRIs): the gradual radiative inspiral of compact objects into massive black holes in galactic centres. These binary systems exhibit highly relativistic and complex orbits, sending off hundreds of thousands of detectable gravitational-wave cycles in the LISA band. These properties make EMRIs the ultimate probe of strong gravity, and a key target for LISA. However, those same properties also make EMRIs extremely challenging to model, with computational approaches used for LIGO binaries — such as numerical relativity — being largely unworkable for such systems. EMRI modeling efforts employ the machinery of black hole perturbation theory, under a dedicated subfield called gravitational self-force theory. The standard two-timescale framework, although successful, is computationally intensive, still greatly incomplete, and far from being ready for LISA data analysis. This project aims to dramatically improve and complement this framework through a hybrid approach that integrates rapid and efficient analytical methods from post-Newtonian theory into gravitational self-force calculations. Specifically, our approach is based on deriving highly accurate analytical approximants for the inspiral evolution through a double expansion in both orbital velocity and mass ratio, to very high order. For the first time, we will apply our method for completely generic, astrophysically realistic, eccentric EMRI configurations, with a spinning primary, orbital plane precession, and the full effect of the first-order self-force, including post-adiabatic conservative corrections. We will also apply our method in the study of black hole scattering with a spinning primary, informing ongoing synergies between self-force theory and effective field theory treatments.