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

Lyapunov Exponents of Rank 2-Variations of Hodge Structures and Modular Embeddings

If the monodromy representation of a VHS over a hyperbolic curve stabilizes a rank two subspace, there is a single non-negative Lyapunov exponent associated with it. We derive an explicit formula using only the representation in the case when the monodromy is discrete.Comment: 22 pages, 4 figures; accepted version to be published in Ann. Inst. Fourier (Grenoble

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