van Bibber Abstract

After three decades, the axion, a hypothetical elementary particle, still represents the best solution to the Strong-CP problem, i.e. why the neutron has a vanishingly small electric dipole moment. Should the axion exist, it would be extremely light, in the range between a micro-eV and milli-eV, and possess extraordinarily feeble couplings to matter and radiation, far below the reach of conventional particle physics experiments. Remarkably, very light axions would have beenproduced abundantly during the Big Bang, and thus the axion also represents a well-motivated dark matter candidate. Being a pseudoscalar, like the neutral pion, the axion can couple to two photons, and as recognized by Pierre Sikivie in 1983, the axion can convert to a single real photon in an external electromagnetic field, an effect historically known as the Primakoff interaction. The coherent mixing of axions and photons in a strong magnetic field of large spatial extent provides the strategy for elegant and ultrasensitive experiments which may finally render the axion observable. This talk will review three major experimental campaigns to discover the axion by coherent axion-photon mixing: the microwave cavity search for halo dark matter axions (AMDX); a search for solar axions (CAST); and purely laboratory experiments, such as photon regeneration ("shining light through the wall"). The searched-for signals are nevertheless still extremely small, and thus axion searches have proven to be a driver for the development of new detector technologies, such as quantum-limited SQUID amplifiers for the microwave cavity experiment. 

Ramond Abstract

No abstract provided.  

Vitev Abstract

I will discuss the mechanisms of production and modification of the yields of rare probes, such as high transverse momentum particles, jets and di-jets, open heavy flavor and quarkonia in nuclear collisions at ultra-relativistic energies. I will emphasize the qualitative similarities and quantitative differences observed or expected for this nuclear modification at RHIC and at the LHC and compare theoretical model predictions to experimental data where relevant. I will point to the relative significance of cold and hot nuclear matter effects and the insight into the QCD dynamics of hard probes that the experimental measurements at vastly different center-of-mass energies provide.  

Ratz Abstract

After reviewing some virtues and problems of the minimal supersymmetric standard model (MSSM), I will show that, if one demands anomaly freedom and fermion masses, only R symmetries can forbid the supersymmetric Higgs mass term mu. I will then prove that R symmetries are not available in conventional grand unified theories (GUTs) and argue that this prevents natural solutions to the doublet-triplet splitting problem in four dimensions. On the other hand, higher-dimensional GUTs do not suffer from this problem. I will briefly discuss an explicit string-derived model in which the mu and dimension five proton decay problems are solved by an order four discrete R symmetry, and comment on the higher-dimensional origin of this symmetry.

Keeler Abstract

We show by explicit construction that for every solution of the incompressible Navier-Stokes equation in p+1 dimensions, there is a uniquely associated "dual" solution of the vacuum Einstein equations in p+2 dimensions. We consider both a "near-horizon" limit in which the (p+1)-dimensional hypersurface Sigma_c becomes highly accelerated, and a long-wavelength hydrodynamic limit. We show that the near-horizon expansion in gravity is mathematically equivalent to the hydrodynamic expansion in fluid dynamics, and the Einstein equation reduces to the incompressible Navier-Stokes equation.