Deep Underground Science and Engineering Lab S1 Dark Matter Working Group

1 Overview The discovery of dark matter is of fundamental importance to cosmology, astrophysics, and elementary particle physics. A broad range of observations from the rotation speed of stars in ordinary galaxies to the gravitational lensing of superclusters tell us that 80–90% of the matter in the universe is in some new form, different from ordinary particles , that does not emit or absorb light. Cosmological observations, especially the Wilkinson Microwave Anisotropy Probe of the cosmic microwave background radiation, have provided spectacular confirmation of the astrophysical evidence. The resulting picture, the so-called " Standard Cosmology, " finds that a quarter of the energy density of the universe is dark matter and most of the remainder is dark energy. A basic foundation of the model, Big Bang Nucle-onsynthesis (BBN), tells us that at most about 5% is made of ordinary matter, or baryons. The solution to this " dark matter problem " may therefore lie in the existence of some new form of non-baryonic matter. With ideas on these new forms coming from elementary particle physics, the solution is likely to have broad and profound implications for cosmology, astrophysics, and fundamental interactions. While non-baryonic dark matter is a key component of the cosmos and the most abundant form of matter in the Universe, so far it has revealed itself only through gravitational effects—determining its nature is one of the greatest scientific issues of our time. Many potential new forms of matter that lie beyond the Standard Model of strong and electroweak interactions have been suggested as dark matter candidates, but none has yet been produced in the laboratory. One possibility is that the dark matter is comprised of Weakly Interacting Massive Particles, or WIMPs, that were produced moments after the Big Bang from collisions of ordinary matter. WIMPs refer to a general class of particles characterized primarily by a mass and annihilation cross section that would allow them to fall out of chemical and thermal equilibrium in the early universe at the dark matter density. Several extensions to the Standard Model lead to WIMP candidates. One that has received much attention is Supersymmetry (SUSY), which extends the Standard Model to include a new set of particles and interactions that solves the gauge hierarcy problem, leads to a unification of the coupling constants, and is required by string theory. The lightest neutral SUSY particle, or neutralino, is thought to be stable and …