Particle Physics

The observed conservation of Baryon and Lepton number may arise because they are gauge symmetries. Models are discussed where Baryon and lepton number are the charges for a spontaneously broken U(1) gauge symmetries. The best of these models is: (1) free of Landau poles that are near the weak scale, (2) has no flavor changing neutral currents at tree level and (3) contains a dark matter candidate.

Recently, several neutrino physics has witnessed an accumulation of anomalous results. In the first part of this talk, we will discuss the tension that the MINOS experiments has seen between oscillations of neutrinos and anti-neutrinos. We will show that, phenomenologically, this tension can be explained if neutrinos are hypothesized to have new interactions mediated by higher-dimensional operators, but we will also show that problems arise when one attempts to embed these operators into renormalizable models. In the second part of the talk, we will address several results hinting at the existence of sterile neutrinos. We will present results from a global fit to worldwide neutrino oscillation data, and will show that one sterile neutrino is not enough to reconcile all data sets, and that 5-neutrino models, while being in much better agreement with the data, still have some tension.

Unexplained hierarchies and the quest for naturalness have driven model-building efforts in particle physics and cosmology for the past few decades. I will speak about various approaches to problems of 'unnatural' fine tunings, in the context of supersymmetry, inflation and LHC phenomenology respectively.

It is often assumed that the first evidence for direct dark matter detection will come from experiments probing spin-independent interactions, because of higher sensitivities due to coherence effects. We explore the possibility of models that would be invisible in such experiments, but detectable via spin-dependent interactions. The existence of much larger (or only) spin-dependent tree-level interactions is not sufficient, due to potential spin-independent subdominant or loop-induced interactions. We find that most models with detectable spin-dependent interactions would also generate detectable spin-independent interactions. Models in which a light pseudoscalar acts as the mediator seem to uniquely evade this conclusion. We present a viable dark matter model generating such an interaction.

After quickly reviewing what we have learned about neutrinos during the past decade, I present an overview of different mechanisms responsible for non-zero neutrino masses, also discussing the possibility of experimentally deciding which one, if any, is correct.

Using the framework of deconstruction, we construct simple, weakly-coupled supersymmetric models that explain the Standard Model flavor hierarchy and produce a flavorful soft spectrum compatible with precision limits. Electroweak symmetry breaking is fully natural/ the mu-term is dynamically generated with no B mu-problem and the Higgs mass is easily raised above LEP limits without reliance on large radiative corrections. These models possess the distinctive spectrum of superpartners characteristic of 'effective supersymmetry': the third generation superpartners tend to be light, while the rest of the scalars are heavy.

Neutrino oscillations has been observed and confirmed at two mass splittings (\Delta m^2), which is consistent with three generations of neutrinos and an unitary mixing matrix. Despite the rapid progress in understanding neutrino oscillations in the last decade, two large questions remain about neutrino oscillation parameters at \Delta m^2 ~ 0.001 eV^2. Is \theta_{23} exactly 45 degrees, indicating an additional symmetry in neutrino mixing? Is \theta_{13} non-zero, which would mean there could be CP violation in the neutrino sector. If \theta_{13} is large enough, then such CP violation could be studied with future high intensity experiments such as the proposed Long Baseline Neutrino experiment in the US (LBNE). The Tokai-To-Kamioka (T2K) long baseline neutrino experiment is designed to precisely measure \nu_{\mu} disappearance (\Delta m^2_{23}, \theta_{23}) and search for \nu_e appearance (\theta_{13}). A beam of muon neutrinos is generated at the J-PARC facility in Tokai-mura, Japan, and is sampled by two near detectors, ND280 and INGRID, before reaching the Super-Kamiokande detector, 295km away. In this talk, a first look at \nu_{\mu} disappearance and \nu_e appearance will be shown from T2K, from the inaugural 6 month run ending in June 2010 (3.23x10^19 protons on target, at 15.5 kW x 10^7s).

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.

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.