Particle theory

Abstract:

The sources of the observed ultrahigh energy cosmic rays must also generate ultrahigh energy neutrinos. Deep inelastic scattering of these neutrinos with nucleons on Earth probe center-of-mass energies s∼100TeV, well beyond those attainable at terrestrial colliders. By comparing the rates for two classes of observable events, any departure from the benchmark (unscreened perturbative QCD) neutrino-nucleon cross section can be constrained. Using the projected sensitivity of the Pierre Auger Observatory to quasihorizontal showers and Earth-skimming tau neutrinos, we show that a "super-Auger" detector can thus provide an unique probe of strong interaction dynamics. © 2006 The American Physical Society.

Abstract:

We attempt to quantify the widely-held belief that large hierarchies induced by strongly-warped geometries are common in the string theory landscape. To this end, we focus on the arguably best-understood subset of vacua -- type IIB Calabi-Yau orientifolds with non-perturbative Kaehler stabilization and a SUSY-breaking uplift (the KKLT setup). Within this framework, vacua with a realistically small cosmological constant are expected to come from Calabi-Yaus with a large number of 3-cycles. For appropriate choices of flux numbers, many of these 3-cycles can, in general, shrink to produce near-conifold geometries. Thus, a simple statistical analysis in the spirit of Denef and Douglas allows us to estimate the expected number and length of Klebanov-Strassler throats in the given set of vacua. We find that throats capable of explaining the electroweak hierarchy are expected to be present in a large fraction of the landscape vacua while shorter throats are essentially unavoidable in a statistical sense.