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VERITAS is an array of four imaging air Cherenkov telescopes located at the Whipple Observatory on Mt. Hopkins, about one hour south of Tucson, AZ. VERITAS is dedicated to the study of gamma-ray astrophysics in the energy range from 100 GeV to 30 TeV. The Fermi Gamma-ray Space Telescope operates in a complementary gamma-ray range, covering 100 MeV to 100 GeV. Together with other similar ground- and space-based instruments (HAWC, H.E.S.S., MAGIC, AGILE), these experiments provide a unique window on the most powerful cosmic particle accelerators, including jets associated with supermassive black holes, shock waves in supernova remnants and the nebulae surrounding energetic pulsars, and the complex physics of X-ray binary systems. Very-high-energy gamma rays can also probe some of the most important questions in particle physics and cosmology: the search for dark matter, Lorentz invariance violation, and the strength of the magnetic field in intergalactic space. We are also deeply involved in a world-wide project to develop and build a next-generation ground-based instrument, the Cherenkov Telescope Array, with a factor of 10 better sensitivity and much broader energy range.

At Columbia and Barnard, the science problems we focus on are in the areas of dark matter searches, the origins of Galactic cosmic rays, and the physics of active galactic nuclei. In many dark matter scenarios, the particles that make up the dark matter can either annihilate with each other, or decay (with a very long lifetime). In either case, one of the final products will be high-energy gamma rays. The mass of the dark matter particle is poorly constrained; above a few hundred GeV, detection of gamma rays from regions of space with unusually high concentrations of dark matter (such as dwarf spheroidal galaxies, or the central region of the Milky Way galaxy) becomes one of the most promising avenues for identifying dark matter.

For just over 100 years we have known that the earth is bombarded by energetic charged particles, cosmic rays, without a clear understanding of their origins. Cosmic rays can range in energy up to 10^20 eV. Up to 10^15 eV or so, cosmic rays are believed to be accelerated within our galaxy, and only recently has unambiguous evidence for cosmic-ray acceleration in supernova remnants (SNRs) emerged, particularly from Fermi-LAT. It remains an open question whether SNRs are the sole, or even the primary, source, along with how the acceleration process works, and how cosmic rays escape from SNRs and diffuse into the galaxy from the regions surrounding them. Deep studies of known Galactic accelerators and surveys of classes of objects will allow us to address this question, as well as explore the details of the acceleration process.

Active galactic nuclei (AGN) are supermassive black holes at the centers of galaxies which are actively accreting material; energy released from the accretion disk somehow powers the formation of relativistic jets of material moving outward from the black holes, as well as acceleration of particles to very high energies. Where and how this particle acceleration occurs, and how it connects to the structure and formation of these remarkable jets, are a few of the questions being addressed by studies of AGN from the radio through the gamma-ray bands.