120215184
A search for gamma radiation above 24 TeV energy from cosmic point sources
Abstract The HEGRA collaboration has searched for γ-ray emission from 36 potential cosmic point sources with the wide angle air Cerenkov detector AIROBICC which is part of the HEGRA cosmic ray detector complex on La Palma. AIROBICC has a γ-ray energy threshold of around 24 TeV and a mean angular resolution of 0.29 °. None of the sources could be found. Upper limits to their fluxes are given. For the VHE γ-ray emitters, the Crab nebula and Mrk 421, these flux limits are below those extrapolated from lower energy observations. Our lower limit for Mrk 421 might be interpreted either as being due to an energy cut-off in the acceleration mechanism or to the onset of γ-interaction with photons of the universal infrared background.
210155517
The IceCube Neutrino Observatory VI: Neutrino Oscillations, Supernova Searches, Ice Properties
IceCube DeepCore can study atmospheric neutrino oscillations through a combination of its low energy reach, as low as about 10 GeV, and its unprecedented statistical sample, of about 150,000 triggered atmospheric muon neutrinos per year. With the diameter of the earth as a baseline, the muon neutrino disappearance minimum and tau neutrino appearance maximum are expected at about 25 GeV, which is considerably lower energy than typical IceCube neutrino events, but higher than the energies at which accelerator-based experiments have detected oscillations. νμ disappearance and ντ appearance from neutrino oscillation can be measured in IceCube DeepCore. We present here the status of the newly developed low energy reconstruction algorithms, the expected experimental signatures, and the proposed approach for such neutrino oscillation measurements. Corresponding authors: Sebastian Euler (seuler@icecube.wisc.edu), Laura Gladstone(gladstone@icecube.wisc.edu), Jason Koskinen(koskinen@psu.edu), Donglian Xu(dxu@crimson.ua.edu) III. Physikalisches Institut, RWTH Aachen University, D-52056 Aachen, Germany Dept. of Physics, University of Wisconsin, Madison, WI 53706, USA Dept. of Physics, Pennsylvania State University, University Park, PA 16802, USA Dept. of Physics and Astronomy, University of Alabama, Tuscaloosa, AL 35487, USA
2219103
AMANDA - first running experiment to use GRID in production
The Grid technologies are in ongoing development. Using current Grid toolkits like the Globus toolkit gives one the possibility to build up virtual organizations. Although these tookits are in still under development and do not feature all functionality, they can already now be used to set up an efficient computing environment for physics collaborations with only moderate work. We discuss in this paper the use of such a computing structure in two running experiments - the AMANDA (AMANDA = Antarctic muon and neutrino detector array) neutrino telescope and the D0 experiment at Tevatron, Fermilab. One of the main features of our approach is to avoid reprogramming of the existing software which is based on several programming languages (FORTRAN, C/C++, JAVA). This was realized with software layers around the collaboration software taking care about in- and output, user notification, tracking of running jobs, etc. A further important aspect is the resolution of library dependencies, which occur when a user runs self-compiled jobs on machines, where these libraries are not installed. These dependencies are also resolved with this layers.
40898720
A fast embedded system for radio detection of cosmic rays
For the detection of radio signals from ultra high energy (> 1017 eV) cosmic rays in the frequency range up to 80 MHz an embedded system was designed, built, and tested. A steep band-pass filter in the range of 30 to 80 MHz suppresses the main source of radio frequency interferences. To fulfill the data acquisition (DAQ) task, four 180 MHz twelve bit ADCs have to be read-out by a FPGA into a two gigabyte buffer memory. Furthermore the FPGA contains the trigger and a Altera NIOS II soft-core processor for data management. A GPS receiver controls the timing of the system. For the read-out an Ethernet-link and a CAN interface to a WLAN communication board is foreseen. The architecture of the system and the measured performance of the DAQ-board are described.
1694798
Design and performance of the lead-concrete geiger tower array within the HEGRA experiment
Abstract The HEGRA experiment is a hybrid installation characterized by four different types of detectors (scintillator counters, open Cherenkov counters, Cherenkov telescopes and Geiger towers) located within one detector array. The Geiger towers are built with the objective to measure the local energy deposition and to reconstruct and identify muon tracks. In addition each tower may serve as an independent high resolution muon flux monitor. With these properties the Geiger towers are operating as geometric and energetic calibration instruments for the other detector components and as additional independent measurement instruments with respect to the γ-hadron separation and the measurement of the chemical composition. In this paper the design, the performance, and the basic principles of the data analysis of the lead-concrete Geiger towers are described.
123338629
IceCube: A Multipurpose Neutrino Telescope
IceCube is a new high-energy neutrino telescope which will be coming online in the near future. IceCube will be capable of measuring fluxes of all three flavors of neutrino, and its peak neutrino energy sensitivity will be in the TeV–PeV range. Here, after a brief description of the detector, we describe its anticipated performance with a selection of physics topics: supernovae, extraterrestrial diffuse and point sources of neutrinos, gamma-ray bursts, neutrinos from WIMP annihilation, and cosmic ray composition.
17033795
Metastable flux configurations and de Sitter spaces
Abstract We derive stability conditions for the critical points of the no-scale scalar potential governing the dynamics of the complex structure moduli and the axio-dilaton in compactifications of type IIB string theory on Calabi–Yau three-folds. We discuss a concrete example of a T 6 orientifold. We then consider the four-dimensional theory obtained from compactifications of type IIB string theory on non-geometric backgrounds which are mirror to rigid Calabi–Yau manifolds and show that the complex structure moduli fields can be stabilized in terms of H RR only, i.e. with no need of orientifold projection. The stabilization of all the fields at weak coupling, including the axio-dilaton, may require to break supersymmetry in the presence of H NS flux or corrections to the scalar potential.
15709187
M theory on eight manifolds
Abstract We show that in certain compactifications of M -theory on eight-manifolds to three-dimensional Minkowski space-time the four-form field strength can have a non-vanishing expectation value, while an N = 2 supersymmetry is preserved. For these compactifications a warp factor for the metric has to be taken into account. This warp factor is non-trivial in three space-time dimensions due to Chern-Simons corrections to the fivebrane Bianchi identity. While the original metric on the internal space is not Kahler, it can be conformally transformed to a metric that is Kahler and Ricci flat, so that the internal manifold has SU (4) holonomy.
15117408
Moduli Stabilization in Non-Geometric Backgrounds
Abstract Type II orientifolds based on Landau–Ginzburg models are used to describe moduli stabilization for flux compactifications of type II theories from the world-sheet CFT point of view. We show that for certain types of type IIB orientifolds which have no Kahler moduli and are therefore intrinsically non-geometric, all moduli can be explicitly stabilized in terms of fluxes. The resulting four-dimensional theories can describe Minkowski as well as anti-de Sitter vacua. This construction provides the first string vacuum with all moduli frozen and leading to a 4D Minkowski background.
10027781
SUPERSYMMETRIC CYCLES IN EXCEPTIONAL HOLONOMY MANIFOLDS AND CALABI-YAU FOUR-FOLDS
We derive in the SCFT and low energy effective action frameworks the necessary and sufficient conditions for supersymmetric cycles in exceptional holonomy manifolds and Calabi-Yau four-folds. We show that the Cayley cycles in Spin(7) holonomy eight-manifolds and the associative and coassociative cycles in G2 holonomy seven-manifolds preserve half of the space-time supersymmetry. We find that while the holomorphic and special Lagrangian cycles in Calabi-Yau four-folds preserve half of the space-time supersymmetry, the Cayley submanifolds are novel as they preserve only one quarter of it. We present some simple examples. Finally, we discuss the implications of these supersymmetric cycles on mirror symmetry in higher dimensions.
14208300
Heterotic cosmic strings
We show that all three conditions for the cosmological relevance of heterotic cosmic strings, the right tension, stability and a production mechanism at the end of inflation, can be met in the strongly coupled M-theory regime. Whereas cosmic strings generated from weakly coupled heterotic strings have the well-known problems posed by Witten in 1985, we show that strings arising from M5-branes wrapped around 4-cycles (divisors) of a Calabi-Yau in heterotic M-theory compactifications solve these problems in an elegant fashion.