Search Talks

On small scales the cosmic microwave background (CMB) is perturbed by large scale structure in the universe, primarily through Compton scattering and gravitational lensing. The current generation of CMB experiments is measuring these signals, allowing new measurements of the build-up of cosmic structure. I will discuss two such measurements being made with the South Pole Telescope: 1) through Compton scattering (the Sunyaev-Zeldovich effect) we have compiled a large catalog of very massive galaxy clusters extending to z>1, allowing a measure of the growth of structure from z=1 to today; 2) we are currently measuring the gravitational lensing of the CMB, providing an accurate measure of the integrated structure between z=0 and z=1100. Both of these are powerful new tests of our cosmological understanding.

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.

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.

I will describe a method to compute from first principles the anomalous dimension of short operators in N=4 super Yang-Mills theory at strong coupling, where they are described in terms of superstring vertex operators in an anti-de Sitter background. I will focus on the Konishi multiplet, dual to the first massive level of the superstring, and compute the one-loop correction to its anomalous dimension at strong coupling, using the pure spinor formalism for the superstring.

The 4D rotating black hole described by the Kerr geometry possesses many of what was called by Chandrasekhar "miraculous" properties. Most of them are related to the existence of a fundamental hidden symmetry of a principal conformal Killing-Yano (PCKY) tensor. In my talk I shall demonstrate that hidden symmetry of the PCKY tensor plays exceptional role also in higher dimensions. Namely, I shall present the most general spacetime admitting the PCKY tensor and show that is possesses the following properties: 1) It is of the algebraic type D and admits the Kerr-Schild form 2) It allows a separation of variables for the Hamilton-Jacobi, Klein-Gordon, Dirac, and stationary string equations. 3) When the Einstein equations with the cosmological constant are imposed the metric describes the most general known (spherical) Kerr-NUT-AdS black hole spacetime. I will also discuss the generalization of Killing-Yano symmetries for spacetimes with natural "torsion 3-form", such as the black hole of D=5 minimal supergravity, or the Kerr-Sen solution of heterotic string theory, and comment on connection to special Riemannian manifolds admiting Killing spinors.

There are good reasons to think that our understanding of particle physics is incomplete. The effective field theory describing the particles that we know about breaks down at the TeV scale, and new effective degrees of freedom must enter. In this talk I will discuss the role that strong dynamics might play in this new physics, focusing on the ways in which approximately scale-invariant dynamics could explain puzzling features of our low-energy Lagrangian. I will also describe recent theoretical and numerical results aimed at constraining the range of behavior that can occur in 4D conformal field theories.

What lies beyond the Standard Model of particle physics? Are there very weakly interacting forms of matter and forces waiting to be discovered? In this talk I will describe some of the efforts underway to detect very weakly interacting particles, from dark matter to new forces. I will discuss recent observations and their theoretical significance as well as the connection to other experimental results. I will conclude with a short summary of the different frontiers and their interrelations.

We show that ordinary and radiative muon capture impose stringent constraints on sterile neutrino properties. In particular, we consider a sterile neutrino with a mass between $40$ and $80~{\rm MeV}$ that has a large mixing with the muon neutrino and decays predominantly into a photon and light neutrinos due to a large transition magnetic moment. Such a model was suggested as a possible resolution to the puzzle presented by the results of the LSND, KARMEN, and MiniBooNE experiments. We find that the scenario with the radiative decay to massless neutrinos is ruled out by measurements of the radiative muon capture rates at TRIUMF in the relevant mass range by a factor of a few in the squared mixing angle. These constraints are complementary to those imposed by the process of electromagnetic upscattering and de-excitation of beam neutrinos inside the neutrino detectors induced by a large transition magnetic moment. The latter provide stringent constraints on the size of the transitional magnetic moment between muon, electron neutrinos and $N$. We also show that further extension of the model with another massive neutrino in the final state of the radiative decay may be used to bypass the constraints derived in this work.

Although the fact that a large fraction of the matter in the universe is non-baryonic is beyond doubt, the exact composition of the dark matter is still shrouded in mystery. Using ultra-sensitive detectors in the deep underground laboratories, physicists are attempting to directly detect dark matter particles streaming from space. At colliders, physicists hope to manufacture large numbers of dark matter particles and study their properties. I will first use an effective field theory approach to demonstrate the power of colliders by comparing these two approaches. I will then describe the recent efforts on measuring dark matter properties at colliders and how imminent discoveries may change our fundamental understanding of physics and the universe.