SEMINAR 2025

Abstract

One of the most interesting sources for LISA are extreme mass ratio inspirals (EMRIs), but these are notoriously challenging to model. The main approach is to solve the Einstein equations pertubatively, in powers of the mass ratio. To obtain accurate waveforms, one requires not only extremely precise models for the adiabatic inspiral (LO in the mass ratio), but also reasonably accurate post-adiabatic waveforms (NLO in the mass ratio). Despite a recent breakthrough, the latter have been extremely difficult to compute throughout parameter space, especially in the dissipative sector – to the point that it is still unclear whether the complete coverage of the parameter space will ready be in time for LISA. In this presentation, I explore the possibility of completing numerical adiabatic eccentric waveforms with post-Newtonian information for the missing post-adiabatic pieces and beyond. Although the resulting hybrid model is less accurate than full post-adibatic waveforms, it could suffice for LISA in a large region of parameter space. The introduction of eccentricity brings many challenges, in particular with respect to gauge invariance and choices of resummations, which I will discuss. In particular, I will present a stepping stone towards the hybrid model: a holistic study of the mapping between fundamental frequencies (radial and azimuthal frequencies) and energy and angular momentum at post-geodesic order.