Massive-neutrino Perturbations without the Boltzmann Hierarchy

At the very foundation of many cosmology studies is a numerical algorithm that evolves the perturbations of matter and radiation from the Big Bang to today. This algorithm spends ~400 differential equations on the Boltzmann hierarchies of photons and 3 generations of massive neutrinos, in contrast to ~5 equations for the rest of the system (i.e. CDM+baryons). I will demonstrate how the line-of-sight integral can be used to replace the neutrino Boltzmann hierarchies, and present a new numerical scheme that can potentially accelerate the current state-of-the-art Boltzmann codes.