Exploring the Universe with Very High Energy Neutrinos

With the discovery of a high-energy neutrino flux in the 0.1 PeV to PeV range from beyond the Earth's atmosphere with the IceCube detector, neutrino astronomy has achieved a major breakthrough in the exploration of the high-energy universe. One of the main goals is the identification and investigation of the still mysterious sources of the cosmic rays which are observed at Earth with energies up to several $10^5$ PeV. In addition to being smoking-gun evidence for the presence of cosmic rays in a specific object, neutrinos escape even dense environments and can reach us from distant places in the universe, thereby providing us with a unique tool to explore cosmic accelerators. This article summarizes our knowledge about the observed astrophysical neutrino flux and current status of the search for individual cosmic neutrino sources. At the end, it gives an overview of plans for future neutrino telescope projects.Comment: 10 pages, 15 figures, to appear in the proceedings of ICHEP 201

IceCube: Neutrino Messages from GRBs

The mystery of where and how Nature accelerates the cosmic rays is still unresolved a century after their discovery. Gamma ray bursts (GRBs) have been proposed as one of the more plausible sources of extragalactic cosmic rays. A positive observation of neutrinos in coincidence with a GRB would identify these objects as sources of the highest-energy cosmic rays and provide invaluable information about the processes occurring inside these phenomena. Calculations show that a kilometer-scale neutrino telescope is necessary for this task. The idea of such a detector is now becoming reality as IceCube at the South Pole nears completion. The contribution reviews the status of the construction and operation of IceCube and summarize the results from searches for neutrinos from GRBs and similar phenomena with IceCube and its predecessor, AMANDA. At the end, an outline of future plans and perspectives for IceCube is given.Comment: 8 pages, 5 figures, proceedings for workshop on "Deciphering the Ancient Universe with Gamma-Ray Bursts", Kyoto, April 2010, to be published by AI

High-energy neutrinos from Galactic sources

Even 100 years after the discovery of cosmic rays their origin remains a mystery. In recent years, TeV gamma-ray detectors have discovered and investigated many Galactic sources where particles are accelerated up to energies of 100 TeV. However, it has not been possible up to now to identify these sites unambiguously as sources of hadronic acceleration. The observation of cosmic high-energy neutrinos from these or other sources will be a smoking-gun evidence for the sites of the acceleration of cosmic rays.Comment: 6 pages, 2 figures; Proceedings of the XIV LCEPP conference (2009), Mosco

Searching for tau neutrinos with Cherenkov telescopes

Cherenkov telescopes have the capability of detecting high energy tau neutrinos in the energy range of 1--1000 PeV by searching for very inclined showers. If a tau lepton, produced by a tau neutrino, escapes from the Earth or a mountain, it will decay and initiate a shower in the air which can be detected by an air shower fluorescence or Cherenkov telescope. In this paper, we present detailed Monte Carlo simulations of corresponding event rates for the VERITAS and two proposed Cherenkov Telescope Array sites: Meteor Crater and Yavapai Ranch, which use representative AGN neutrino flux models and take into account topographic conditions of the detector sites. The calculated neutrino sensitivities depend on the observation time and the shape of the energy spectrum, but in some cases are comparable or even better than corresponding neutrino sensitivities of the IceCube detector. For VERITAS and the considered Cherenkov Telescope Array sites the expected neutrino sensitivities are up to factor 3 higher than for the MAGIC site because of the presence of surrounding mountains.Comment: arXiv admin note: text overlap with arXiv:1308.019

Structure Function Results from ZEUS

This contribution presents recent ZEUS results on proton structure functions at HERA. The inclusive phi(1020)-meson cross section was measured, and it was used to determine the s-quark content of the proton. The structure function F_2 was extracted using initial-state radiative events. Neutral and charged current cross sections were used to extract the structure function xF_3 and measure the mass of the W boson, respectively. A NLO QCD fit to ZEUS data and fixed target cross sections was employed to determine the parton density functions of the quarks and of the gluon inside the proton

The Lazy Flipper: MAP Inference in Higher-Order Graphical Models by Depth-limited Exhaustive Search

This article presents a new search algorithm for the NP-hard problem of optimizing functions of binary variables that decompose according to a graphical model. It can be applied to models of any order and structure. The main novelty is a technique to constrain the search space based on the topology of the model. When pursued to the full search depth, the algorithm is guaranteed to converge to a global optimum, passing through a series of monotonously improving local optima that are guaranteed to be optimal within a given and increasing Hamming distance. For a search depth of 1, it specializes to Iterated Conditional Modes. Between these extremes, a useful tradeoff between approximation quality and runtime is established. Experiments on models derived from both illustrative and real problems show that approximations found with limited search depth match or improve those obtained by state-of-the-art methods based on message passing and linear programming.Comment: C++ Source Code available from http://hci.iwr.uni-heidelberg.de/software.ph

Orientation-dependent binding energy of graphene on palladium

Using density functional theory calculations, we show that the binding strength of a graphene monolayer on Pd(111) can vary between physisorption and chemisorption depending on its orientation. By studying the interfacial charge transfer, we have identified a specific four-atom carbon cluster that is responsible for the local bonding of graphene to Pd(111). The areal density of such clusters varies with the in-plane orientation of graphene, causing the binding energy to change accordingly. Similar investigations can also apply to other metal substrates, and suggests that physical, chemical, and mechanical properties of graphene may be controlled by changing its orientation.Comment: 5 pages, 6 figure

Social uncertainty is heterogeneous and sometimes valuable

To win friends, help the needy, avoid exploitation or influence strangers, people must make decisions that are inherently uncertain. In their compelling and insightful perspective on resolving social uncertainty1, FeldmanHall and Shenhav (henceforth F&S) join a growing movement combining computational approaches with social psychological theory. F&S identify a range of negative and positive aspects of social uncertainty. Here we offer additional ways to think about social uncertainty and suggest potential avenues for future research