  The search for new physics requires a joint experimental and theoretical
effort. Lattice QCD is already an essential tool for obtaining precise
model-free theoretical predictions of the hadronic processes underlying many
key experimental searches, such as those involving heavy flavor physics, the
anomalous magnetic moment of the muon, nucleon-neutrino scattering, and rare,
second-order electroweak processes. As experimental measurements become more
precise over the next decade, lattice QCD will play an increasing role in
providing the needed matching theoretical precision. Achieving the needed
precision requires simulations with lattices with substantially increased
resolution. As we push to finer lattice spacing we encounter an array of new
challenges. They include algorithmic and software-engineering challenges,
challenges in computer technology and design, and challenges in maintaining the
necessary human resources. In this white paper we describe those challenges and
discuss ways they are being dealt with. Overcoming them is key to supporting
the community effort required to deliver the needed theoretical support for
experiments in the coming decade.
