Particle theory

Abstract:

A search for TeV-PeV muon neutrinos from unresolved sources was performed on AMANDA-II data collected between 2000 and 2003 with an equivalent live time of 807 days. This diffuse analysis sought to find an extraterrestrial neutrino flux from sources with nonthermal components. The signal is expected to have a harder spectrum than the atmospheric muon and neutrino backgrounds. Since no excess of events was seen in the data over the expected background, an upper limit of E2Φ90%C.L.<7.4×10-8GeVcm-2s-1sr-1 is placed on the diffuse flux of muon neutrinos with a Φ E-2 spectrum in the energy range 16 TeV to 2.5 PeV. This is currently the most sensitive Φ E-2 diffuse astrophysical neutrino limit. We also set upper limits for astrophysical and prompt neutrino models, all of which have spectra different from Φ E-2. © 2007 The American Physical Society.

Abstract:

We study the dynamics of the finite-temperature phase transition for warped Randall-Sundrum(RS)-like throat models related to the Klebanov-Tseytlin solution. We find that, for infrared branes stabilized near the tip of the throat, the bounce action has a mild N^2 dependence, where N(y) \sim [M_5 L(y)]^{3/2} is the effective number of degrees of freedom of the holographic dual QFT, and where L(y) is the local curvature radius, which decreases in the infrared. In addition, the bounce action is not enhanced by large numbers. These features allow the transition to successfully complete over a wider parameter range than for Goldberger-Wise stabilized RS models. Due to the increase of L(y) in the ultraviolet, the throat has a reliable gravitational description even when the number of infrared degrees of freedom is small. We also comment on aspects of the thermal phase transition in Higgsless models, where the gauge symmetry breaking is achieved via boundary conditions. Such models include orbifold-GUT models and the Higgsless electroweak symmetry breaking theories of Csaki et al., with Standard Model gauge fields living in the bulk.