New twists in compact binary waveform modeling: A fast time-domain model for precession

We present imrphenomtphm, a phenomenological model for the gravitational-wave signals emitted by the coalescence of quasicircular precessing binary black holes systems. The model is based on the ``twisting up'' approximation, which maps nonprecessing signals to precessing ones in terms of a time-dependent rotation which can be described by three Euler angles and which has been utilized in several frequency-domain waveform models that have become standard tools in gravitational-wave data analysis as well as in several time-domain models. Our model is constructed in the time domain, applying the twisting up approximation to the nonprecessing multimode model imrphenomthm, which allows several improvements over the frequency-domain models; we do not use the stationary phase approximation, we employ a simple approximation for the precessing Euler angles for the ringdown signal, and we implement a new method for computing the Euler angles through the evolution of the spin dynamics of the system, which is more accurate and also computationally efficient.