Dufek Abstract - Special Geophysics Colloquium

Many processes in nature involve multiple, mechanically distinct phases: for instance, crystals settling in magmatic systems and ash particles interacting with a turbulent gas phase in an explosive volcanic eruptions. The interactions between these phases shape the landscape of all terrestrial planets, dictate exchanges at the interface of the solid surface and the atmosphere and lead to the large scale differentiation of Earth and other planets. Examples of multiphase flows include explosive volcanic eruptions, Martian dust storms, sediment-choked rivers, crystal and bubble-laden magma chambers and marine turbidity currents. Although extremely common, the cumulative expression of numerous particle-particle and particle-fluid interactions can produce emergent meso-scale structure and self-organization that is difficult to predict. I will address multiphase dynamics in the context of natural high-energy examples: planetary differentiation and volcanic eruptions. I will discuss the use of multiphase models in addressing the different scales of fluid motion in volcanic multiphase flow as well as how they can provide a platform to integrate microphysical, analogue experiments and observational constraints. Microphysical experiments can provide the necessary closure for statistical mechanics based models, and provide a way to examine grain-scale processes in a probabilistic manner. Such small-scale processes can dramatically alter the flow dynamics. One of the primary goals and utilities of this combined approach is that it enables comparison with diverse datasets, integrating previously disparate observations.

Behn Abstract - Special Geophysics Colloquium

During summer months, supra-glacial melt water lakes form across the ablation zone of the Greenland Ice Sheet. Many of these lakes grow in size up to 2-5 km in diameter before draining rapidly (in minutes to hours) via hydro-fracture. These drainage events deliver large volumes of water to the ice sheet bed and create conduits (e.g., moulins) that provide surface-to-bed drainage channels that remain open for the remainder of the summer melt season. This rapid influx melt water in turn influences ice sheet dynamics by modulating basal water pressure and frictional sliding at the ice-bed interface. I will present GPS and seismic data from a network of stations operational from 2006-2013 surrounding a supra-glacial lake system in the Jakobshavn-Isbrae region of the Greenland Ice Sheet. These data are used to (1) invert for the opening history of the hydro-fracture beneath the lake in space and time, and (2) evaluate the acceleration of the ice in response to the rapid influx of surface meltwater to the bed. Our data show that ice sheet response is strongly modulated by the seasonal evolution of the subglacial hydrologic system. Lake drainages that occur early in the summer melt season have a larger and more prolonged effect on ice dynamics compared to those occurring later in the melt season. I speculate that this reflects a less efficient early season hydrologic system, which cannot rapidly evacuate the influx of melt water associated with lake drainage, allowing basal water pressure to remain high and promoting sliding. Finally, I will discuss how these individual drainage events scale up to influence regional dynamics along the western margin of the Greenland Ice Sheet.

Meurice Abstract

The classical O(2) model on an isotropic Euclidean space-time lattice has many common features with the models studied by lattice gauge theorists. The continuum limit in the time direction leads to an Hamiltonian describing coupled abelian rotors on a space lattice. When a large chemical potential is introduced, it is possible to qualitatively map the abelian rotor model into a Bose-Hubbard model. We use the tensor renormalization group (TRG) formulation of the classical nonlinear sigma O(2) model with time link couplings beta_t, space link coupling beta_x and a chemical potential mu to show that this qualitative picture is quantitatively correct. We map the phase diagrams of the isotropic beta_t = beta_x and the time continuum limit beta_t >> beta_x into each other and with the Bose-Hubbard model by a change of coordinates in the beta-mu plane. We check our numerical results with the worm algorithm at small volume. We discuss the possibility of constructing Bose-Hubbard models that can describe the isotropic O(2) model on an isotropic Euclidean lattice and without chemical potential.

This is work done with Haiyuan Zou, Yuzhi Liu, S. Chandrasekharan, J. Unmuth-Yockey, A. Bazavov, C.-Y. Lai, and S.-W. Tsai.

Ramond Abstract

We introduce a framework for flavor symmetries based on the finite subgroup of SU(3), Z_7 "rtimes" Z_3. A part of the ring uses a special Majorana matrix, natural under this symmetry. Closing the ring is not yet finished, but the results of a numerical search severely restricts its possibilities. The analysis is presented for both tribimaximal and bimaximal seesaw mixings.

Murphy Abstract - Special Geophysics Colloquium

Earth's metallic core is thought to be made up primarily of iron, and comprises a solid inner region surrounded by a liquid outer region. Directly observing these remote layers is challenging, but seismologists have constrained their density and elastic wave speeds using normal modes and body waves excited by large earthquakes. Moreover, geodynamic models of the outer core provide insight into the dynamics and physical properties of the convecting metallic liquid. As a Mineral Physicist, my approach to improving the current understanding the Earth's core is to accurately measure the high-pressure physical properties of iron and iron alloys, in order to provide a solid experimental baseline against which to compare these observations and models. In particular, I have measured pressure-volume relationships and the high-pressure phonon density of states of iron and iron alloys using diamond-anvil cells and advanced radiation sources, such as the Advanced Photon Source and Spallation Neutron Source. I will show how my complementary datasets provide valuable insight into the structural, elastic, and thermodynamic properties of pure iron and iron alloys to core pressures and, in turn, shed light on the composition and dynamics of Earth's core.

DeTar Abstract

Precision tests of the standard model could reveal signs of more fundamental processes. The Fermilab Lattice and MILC collaborations have been using lattice QCD to calculate the hadronic form factors for the semileptonic processes B -> D l ν and B -> D* l ν. I will present results of the calculation, which, when combined with experimental measurements, provide the most precise results to date for the Cabibbo-Kobayashi-Maskawa matrix element |V_cb|. This matrix element figures prominently in precision tests of the standard model.

Phelps Abstract

Dark matter is thought to make up ~27% of the energy density of the universe, outweighing normal matter by a factor of ~6, yet no direct detection of a dark matter particle has ever been confirmed. Currently, Weakly Interacting Massive Particles, or WIMPs, are the leading candidate for particle dark matter. The Large Underground Xenon (LUX) detector has recently published its first dark matter cross-section upper-limit, becoming the world's leading WIMP search, in conflict with several previous claimed hints of discovery. In this talk, I will review the LUX detector, discuss the recent result and provide an update on next steps in the LUX program.

Liptak Abstract

Neutrinoless double beta decay (0νββ) is a theorized process offering a window into physics beyond the Standard Model. In addition to providing the first direct measurement of neutrino mass, its observation would have ramifications in numerous open questions, including the absolute neutrino mass scale, mass hierarchy, and the nature of neutrinos as Dirac or Majorana particles. The NEMO-3 experiment utilized a unique combination of tracking and calorimetry to provide precision sensitivity and in situ background rejection, ultimately setting several world's-best half-life limits. This talk will focus on results from the search for 0νββ in ¹¹⁶Cd and ⁸²Se, as well as the development of calorimetry simulations for the next-generation detector, known as SuperNEMO.

Lebed Abstract

Flanagan Abstract

New physics beyond the Standard Model continues to allude LHC experimentalists. One such allusive theory is Supersymmetry (SUSY). One possible explanation for this lack of discovery is that colored SUSY particles are out of the reach of the LHC. In such a case, Vector Boson Fusion (VBF) processes are a powerful tool to search for electroweak SUSY particles directly, particularly in compressed spectra. This talk will discuss the status quo of such SUSY searches at CMS as well as future searches. Surprisingly, VBF also holds promise for colored SUSY searches in otherwise challenging scenarios such as `Rubicon' regions where the top squark mass is roughly equal to the neutralino plus top quark mass. We will also discuss the promise and challenges of these searches at 14 TeV [arXiv:1312.1348].

Hook Abstract

We propose a method for systematically understanding the IR of nonsupersymmetric gauge theories. Starting from a known S-duality of supersymmetric theories realized on the worldvolume of D3 branes in type IIB string theory, a new duality is obtained by replacing the D3-branes with antibranes. Large classes of dual pairs of nonsupersymmetric theories can be obtained in this way, with different interactions and matter content (chiral and vector-like). A theory with anti-symmetrics is argued to have confinement in a fermion quadlinear rather than a fermion bilinear. An interesting QCD like theory is found as well. The IR dynamics include chiral symmetry breaking and massless fermions.