Search Talks

How do we weigh the Universe? Where is the Dark Matter? I will discuss these questions and show that several independent methods, including the observed present-day abundance of rich clusters , the evolution of cluster abundance with redshift, the baryon-fraction in clusters, the observed Mass-to-Light function from galaxies to superclusters, and other large-scale structure observations, all reveal a universe with a low mass density parameter of ~20% of the critical density. The data suggest that the mass in the Universe, including the dark-matter, approximately follows light on large scales and that most of the mass resides in huge dark halos around galaxies. I will review the combined observational evidence for dark-matter and for dark-energy in the universe and their cosmological implications.

The particle physics community is bubbling with excitement since the recent discovery in the cosmic radiation of a positron and electron excess at high energy. This may be the first indirect hint that dark matter particles wander in the halo of the Milky Way. However, these species do not seem to have the expected properties. I will review the various pieces of that puzzle and present a status report of the current developments in that fast moving field.

Although most realistic approaches to quantum theory are based on classical particles, QFT reveals that classical fields are a much closer analog. And unlike quantum fields, classical fields can be extrapolated to curved spacetime without conceptual difficulty. These facts make it tempting to reconsider whether quantum theory might be reformulated on an underlying classical field structure. This seminar aims to demonstrate that by changing only how boundary conditions (BCs) are imposed on ordinary classical field equations, a psi-epistemic quantum theory naturally emerges. Uncertainty and basic quantization naturally result from imposing BCs on closed hypersurfaces (as in Lagrangian QFT); further quantization results from extending Hamilton's principle to restrict the BCs as well as the field equations. The partial dependence of field parameters on future BCs implies an effective contextuality, naturally avoiding the usual arguments against realistic quantum models. Successful applications to the relativistic scalar field will be presented, further motivating an ambitious research program of reformulating quantum theory in terms of ontic classical fields.

Strongly warped regions, or throats, are a common feature of string theory compactifications. In the early, hot universe, energy will be transferred between these throats and between throats and the standard model. Using the gauge-gravity duality, we calculate the rate of this energy transfer. Due to the warping, the resulting decay rate of throat-localized Kaluza-Klein states to other throats or the standard model is strongly suppressed. If their lifetime is longer than the current age of the universe, these states are an interesting dark matter candidate. We discuss a scenario along these lines.

Light hidden sectors are a generic possibility for new physics, and recent astrophysical signals motivate hidden sector dark matter. I will discuss probes of a minimal secluded U(1) hidden sector scenario with high luminosity particle physics experiments.

The XENON project pursues the goal of directly detecting nuclear recoils resulting from scattering interactions with Weakly Interacting Massive Particles (WIMPs), using a phased approach of increasingly more sensitive experiments. The detector consists of a dual-phase liquid/gas xenon time projection chamber, which can measure down to ~2 keV(ee) energy threshold and discriminates against background using both the primary scintillation light and the charge signal resulting from interactions in the noble liquid. The current exeriment XENON100 is the successor of the highly successful XENON10 detector, featuring 10 times greater sensitive mass and 100 times lower background. Its sensitivity with an ultimate exposure of 6000 kg days will be 2 times 10^{-45} cm^2 for spin-independent interactions at 100 GeV/c^2. XENON100 has been installed and is operating. I will report on the present status and discuss its physics reach along with future prospects of detectors at the ton scale.

The DEAP/CLEAN collaboration will be constructing a 3600-kg single-phase liquid-argon dark matter detector at SNOLAB with sensitivity to 10-46 cm2 for a 100 GeV WIMP. We are currently operating a 7-kg liquid-argon detector (DEAP-1) at SNOLAB. Using DEAP-1 we have made measurements of alpha surface activity and radon levels in the detector. We have also performed studies of pulse-shape discrimination to separate electromagnetic interactions in the liquid argon from nuclear recoils. Recently published data from surface at Queen’s University showed no contamination in the WIMP signal region from 16.7 Million tagged gamma events in WIMP the region of interest. A further 22 M events have been accumulated at SNOLAB with no contamination. The design of the DEAP-3600 detector will be presented with emphasis on reduction of backgrounds, including design of a resurfacer to remove radon daughters which plate out on acrylic and the design of the acrylic container to plate shield against neutron activity from the PMTs and steel outer vessel.