Origin of the NuLib remnant drift

Determine the cause of the substantial remnant drift observed in the NuLib charged-current opacity simulations of binary neutron-star mergers.

Background

The simulations using the NuLib charged-current interaction rates exhibit a substantial drift of the merger remnant that persists across numerical resolutions and affects the interpretation of the thermodynamic evolution. The drift induces kinetic energy in the remnant and thereby contaminates the conserved internal-energy variable, with amplified consequences for the inferred temperature and neutrino interaction rates. The paper reports the effect and applies positional corrections where relevant, but does not identify its origin.