Physics at the Intensity Frontier
The Standard Model of Particle Physics succeeds brilliantly at explaining the nature of the physical universe, but it leaves many open questions. Despite the development of myriad intriguing theories to address these questions, ultimately only experiment can light the way to discovery. In our own time, experiments at the energy frontier can search directly for new phenomena beyond the Standard Model. Alongside the compelling physics of Terascale explorations at the LHC and the ILC, another window on discovery has opened with the remarkable recent developments in neutrino science and with the ability to detect new physics phenomena in ultrarare events or in the small perturbations they induce in other processes. This chapter focuses on accelerator-based opportunities at the intensity frontier. Experiments in symmetry-violating processes and rare decays can provide windows into new mass scales of many thousands of TeV. Neutrino experiments may tell us about physics at even higher energies near unification or about an entirely new source of CP violation that may help explain the excess of matter over antimatter in the universe.