Lightcone Construction for HACC Cosmological Simulations with LANTERN

Abstract: This document describes the LANTERN (Lightcone generAtion via sNapshoT intERpolatioN) code module, our current approach for generating lightcones from HACC [5] simulation products. In sec. 1, we derive the condition which defines all spacetime events that can be seen by an observer at any given time (we parameterize the surface of the observer's past lightcone). In sec. 2, we describe how we apply this condition to find approximate lightcone-crossing times of objects whose positions and velocities are known only at discrete time snapshots. Higher order effects and corrections are discussed in sec. 3. Sec. 4 describes simulation box replication capabilities that allow generation of arbitrary lightcone sizes.