  Within the next decade, experimental High Energy Physics (HEP) will enter a
new era of scientific discovery through a set of targeted programs recommended
by the Particle Physics Project Prioritization Panel (P5), including the
upcoming High Luminosity Large Hadron Collider (LHC) HL-LHC upgrade and the
Deep Underground Neutrino Experiment (DUNE). These efforts in the Energy and
Intensity Frontiers will require an unprecedented amount of computational
capacity on many fronts including Monte Carlo (MC) detector simulation. In
order to alleviate this impending computational bottleneck, the Celeritas MC
particle transport code is designed to leverage the new generation of
heterogeneous computer architectures, including the exascale computing power of
U.S. Department of Energy (DOE) Leadership Computing Facilities (LCFs), to
model targeted HEP detector problems at the full fidelity of Geant4. This paper
presents the planned roadmap for Celeritas, including its proposed code
architecture, physics capabilities, and strategies for integrating it with
existing and future experimental HEP computing workflows.
