Active-learning emulators for nuclear two-body scattering in momentum space

We extend the active learning emulators for two-body scattering in coordinate space with error estimation, recently developed in arXiv:2504.06092, to coupled-channel scattering in momentum space. Our full-order model (FOM) solver is based on the Lippmann-Schwinger integral equation for the t-matrix as opposed to the radial Schrodinger equation in coordinate space. We use (Petrov-)Galerkin projections and high-fidelity calculations at a few snapshots in the parameter space of the interactions to construct efficient reduced-order models (ROMs), enriched by a greedy algorithm for snapshot selection. Google JAX allows us to implement both the FOM solver and the corresponding ROMs very efficiently in Python. We present results for emulating cross sections and scattering phase shifts in coupled and uncoupled channels, and assess the accuracy of the developed ROMs and their computational speed-up factors. The software framework for reproducing and extending our results will be made publicly available, setting the stage for calibrating chiral nuclear interactions and optical models against scattering data with quantified errors. We also demonstrate that Bayesian parameter estimation of chiral NN forces with quantified emulator errors is feasible