Search Talks

The DEAP-3600 single-phase liquid-argon dark matter detector is under construction at SNOLAB. The fundamental goal of the design is to increase the volume of the detector while having the liquid argon contact the smallest possible surface comprising only clean acrylic and wavelength shifter. Specifically DEAP-3600 is a spherical detector with a 1000 kg fiducial mass and a design background rate less than 0.1 events in the WIMP region of interest in three years of data taking. Design sensitivity to WIMP dark matter at 100 GeV is 10-46 cm2. In order to achieve this ambitious goal an extensive program of background reduction and control is underway for all detector components including the acrylic vessel, process system, photomultiplier tubes and TPB wavelength shifter. Efforts to obtain acrylic with bulk Uranium and Thorium contamination below 0.3 and 1.3 ppt respectively and Pb-210 contamination below 1.1x10-8 ppt will be described. A resurfacer is under development to ensure that the surface contamination of acrylic is removed. Even with these stringent controls fiducialization will be required to reduce surface backgrounds by a factor of 1000. Preliminary studies are promising. We have operated the DEAP-1 prototype detector underground at SNOLAB; results from the DEAP-1 runs will be discussed and the impact of those runs on DEAP-3600 will be discussed. SNOLAB has recently made the “phase 2” expansion (including the cryopit and two drifts) part of the clean space. A photo essay showing recent progress in the facility and the experimental program will be presented.

The standard method to study nonperturbative properties of quantum field theories is to Wick rotate the theory to Euclidean space and regulate it on a Euclidean Lattice. An alternative is "fuzzy field theory". This involves replacing the lattice field theory by a matrix model that approximates the field theory of interest, with the approximation becoming better as the matrix size is increased. The regulated field theory is one on a background noncommutative space. I will describe how this method works and present recent progress and surprises.

If the universe is a quantum mechanical system it has a quantum state. This state supplies a probabilistic measure for alternative histories of the universe. During eternal inflation these histories typically develop large inhomogeneities that lead to a mosaic structure on superhorizon scales consisting of homogeneous patches separated by inflating regions. As observers we do not see this structure directly. Rather our observations are confined to a small, nearly homogeneous region within our past light cone. This talk will describe how the probabilities for these observations can be calculated from the probabilities supplied by the quantum state without introducing a further ad hoc measure. The talk will emphasize the principles behind this result --- a quantum state, quantum spacetime leading to an ensemble of classical histories, quantum observers, a focus in local observations, and the use of coarse-grainings adapted to these observations. The principles will be illustrated in simple models in particular using the no-boundary wave function as a model of the quantum state. Applied to a model landscape we obtain specific predictions for features of the CMB spectrum and improvements in the `anthropic' bounds on the cosmological constant.

We present a new formulation of quantum mechanics for closed systems like the universe using an extension of familiar probability theory that incorporates negative probabilities. Probabilities must be positive for alternative histories that are the basis of settleable bets. However, quantum mechanics describes alternative histories are not the basis for settleable bets as in the two-slit experiment. These alternatives can be assigned extended probabilities that are sometimes negative. We will compare this with the decoherent (consistent) histories formulation of quantum theory. The prospects for using this formulation as a starting point for testable alternatives to quantum theory or further generalizations of it will be briefly discussed.

I discuss how the results of dark matter experiments can be used to draw conclusions about the nature of WIMP dark matter that are to a large extent model-independent. Specifically, I show that combining the results of direct detection experiments with data from neutrino telescopes can help establish whether the dark matter particle is its own anti-particle. I go on to discuss how limits on the diffuse and line spectra obtained from gamma ray telescopes can be used to constrain the annihilation modes of dark matter.