2,866 research outputs found

    Weak Interactions in Supernova Cores and Saturation of Nucleon Spin Fluctuations

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    Extrapolation of perturbative nucleon spin fluctuation rates seems to suggest a strong suppression of weak interactions in supernova cores. We derive a new sum rule for the dynamical spin-density structure function which relates the spin fluctuation rate to the average nuclear interaction energy. For a bremsstrahlung like structure function profile we show that instead of strongly decreasing, the neutrino scattering cross section is roughly density independent and axion emission rates increase somewhat slower than the lowest order emissivities towards the center of a hot supernova core.Comment: 9 latex pages, 1 uuencoded postscript figure added via figures comman

    Ultra-High Energy Cosmic Rays: A Probe of Physics and Astrophysics at Extreme Energies

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    The origin of cosmic rays is one of the major unresolved questions in astrophysics. In particular, the highest energy cosmic rays observed possess macroscopic energies and their origin is likely associated with the most energetic processes in the Universe. They thus provide a probe of physics and astrophysics at energies that are unreached in laboratory experiments. Theoretical explanations range from acceleration of charged particles in astrophysical environments to particle physics beyond the well established Standard Model, and processes taking place at the earliest moments of our Universe. Distinguishing between these scenarios requires detectors with effective areas in the 1000 km^2 range which are now under construction or in the planning stage. Close connections with gamma-ray and neutrino astrophysics add to the interdisciplinary character of this field.Comment: 21 latex pages, 4 postscript figures included; preprint version of recent Science review article; for journal version link see http://www.iap.fr/users/sigl/uhecrpub.htm

    Lectures on Astroparticle Physics

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    These are extended notes of a series of lectures given at the XIth Brazilian School of Cosmology and Gravitation. They provide a selection of topics at the intersection of particle and astrophysics. The first part gives a short introduction to the theory of electroweak interactions, with specific emphasize on neutrinos. In the second part we apply this framework to selected topics in astrophysics and cosmology, namely neutrino oscillations, neutrino hot dark dark matter, and big bang nucleosynthesis. The last part is devoted to ultra high energy cosmic rays and neutrinos where again particle physics aspects are emphasized. The often complementary role of laboratory experiments is also discussed in several examples.Comment: 42 pages, 12 figures, extended version of lectures given at the XIth Brazilian School of Cosmology and Gravitation, Rio de Janeiro, July 26 - August 4, 2004, prepared for AIP conference proceeding

    Cosmic Radiation Constraints on Low String Scale and Extra Dimension Cross Sections

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    The observed interaction energy of cosmic rays with atmospheric nuclei reaches up to a PeV in the center of mass. We compute nucleon-nucleon and nucleon-neutrino cross sections for various generic parton cross sections appearing in string and brane world scenarios for gravity and compare them with cosmic ray data. Scenarios with effective energy scales in the TeV range and parton cross sections with linear or stronger growth with the center of mass energy appear strongly constrained or ruled out. String-inspired scenarios with infinite-volume extra dimensions may require a fundamental scale above 100 eV for which they are probably in conflict with gravity on parsec scales.Comment: 4 revtex pages, 1 postscript figur

    Ultrahigh Energy Neutrinos and Cosmic Rays as Probes of New Physics

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    Cosmic high energy neutrinos are inextricably linked to the origin of cosmic rays which is one of the major unresolved questions in astrophysics. In particular, the highest energy cosmic rays observed possess macroscopic energies and their origin is likely to be associated with the most energetic processes in the Universe. Their existence triggered a flurry of theoretical explanations ranging from conventional shock acceleration to particle physics beyond the Standard Model and processes taking place at the earliest moments of our Universe. Furthermore, many new experimental activities promise a considerable increase of statistics at the highest energies and a combination with gamma-ray and neutrino astrophysics will put strong constraints on these theoretical models. The detection of ultra high energy neutrinos in particular is made likely by new experimental techniques and will open an important new channel. We give an overview over this quickly evolving field with special emphasize on new experimental ideas and possibilities for probing new physics beyond the electroweak scale.Comment: 44 latex pages, 8 postscript figures included; based on lectures given at summer schools in Kopenhagen and Parma (2001). for reviews see also http://www.iap.fr/users/sigl/uhecrpub.htm

    Egyptian pit-looms from the late first millennium AD — attempts in reconstruction from the archaeological evidence

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    In discussions on the development of weaving technology, specifically treadle looms in the Mediterranean area, Egypt is often referred to as one of the earliest countries in which people used foot-powered looms for producing cloth. It is thought to have been in regular use in the production of cloth as early as the second half of the 1st millennium AD. This belief is built on results from excavations undertaken during the early 20th century by the Egypt Exploration Fund at the hill of Sheikh Abd el-Qurna in Luxor, as well as on textile studies. Unfortunately, none of the postulated looms has ever been found and no pictorial evidence has survived illustrating the apparatus that the weavers worked on. Texts provide only scant information, none of which is sufficiently descriptive. For the reconstruction of the weaving device used in Egypt during the Late Roman and Early Islamic periods one therefore depends on the scarce archaeological and architectural information from excavations. This consists predominantly of pits, which were identified by Herbert E. Winlock as substructures of a horizontal treadle loom. However, Winlock’s identification was criticised by various researchers, and subsequently his suggestion was disproved by the experimental reconstruction of a loom within one of the pits of the monastery of Epiphanius, as well as the comparison with more recent archaeological evidence. Although Winlock was with much certainty correct in proposing that the pits were once loom emplacements, the type and features of the weaving apparatus are still uncertain

    High Energy Neutrino Astronomy: WIN 99

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    Although high energy neutrino astronomy is a multidisciplinary science, gamma ray bursts have become the theoretical focus since recent astronomical observations revealed their potential as cosmic particle accelerators. This spotlight is shared with investigations of the potential of high energy telescopes to observe oscillating atmospheric neutrinos. The Superkamiokande results have boosted atmospheric neutrinos from a calibration tool and a background for doing astronomy, to an opportunity to confirm the evidence for neutrino mass. Nevertheless, the highlights are mostly on the experimental front with the completion of the first-generation Baikal and AMANDA detectors. Neutrino signals from the Lake Baikal detector bode well for the flurry of activities in the Mediterranean. The completed AMANDA telescope announced first light, neutrinos actually, at this meeting.Comment: 14 pages, Latex2.09, uses sprocl.sty and epsf.sty, 5 postscript figures. Talk presented at the 17th International Workshop on Weak Interactions and Neutrinos, Cape Town, South Africa, January 199