Most of the matter in the universe is unlike anything ever detected in a terrestrial laboratory. This so-called dark matter seems to neither absorb nor emit light or energy, making it challenging to study with the conventional tools of high-energy physics. Despite a decades-long effort to measure dark matter particle interactions, direct detection remains elusive, and our most reliable information about dark matter comes from astronomical observations of its gravitational influence.
The cosmological expansion is accelerating, defying expectations based on the universally attractive nature of ordinary gravitating matter. Identifying the physical nature of the “dark energy” driving the cosmic acceleration is one of the major goals of present-day fundamental physics. Considerable ongoing effort is dedicated to discriminating between models for dark energy, which include a new, scalar “quintessence” field with a time-evolving equation of state; a failure of general relativity as the fundamental theory of gravity on cosmological scales; or a cosmological constant that is many orders of magnitude smaller than elementary expectations. While little is known about the cause of the cosmic acceleration, what is clear is that this observation challenges the foundations of modern cosmology as well as of particle physics.
The science of the dark universe is a focal point of the research carried out by the CPAC group. We are deeply involved in numerous activities that will yield new insight into dark matter and dark energy, including ongoing surveys such as the South Pole Telescope (SPT) and the Dark Energy Survey (DES), and near-future experiments such as the Large Synoptic Survey Telescope (LSST) and the Dark Energy Spectroscopic Instrument (DESI). Our group has developed the Hardware Accelerated Cosmology Code (HACC) to run some of the world’s largest simulations of cosmological structure formation. We have pioneered new techniques to transform cosmological simulations into realistic synthetic skies that can be compared directly to observations from these and other astronomical surveys.