Lightcone Construction for HACC Cosmological Simulations with LANTERN
  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.
