115 research outputs found

    Ultrahigh Energy Neutrinos

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    The ultrahigh energy neutrino cross section is well understood in the standard model for neutrino energies up to 1012^{12} GeV. Test of neutrino oscillations (νμ↔ντ\nu_\mu\leftrightarrow\nu_\tau) from extragalactic sources of neutrinos are possible with large underground detectors. Measurments of horizontal air shower event rates at neutrino energies above 1010^{10} GeV will be able to constrain nonstandard model contributions to the neutrino-nucleon cross section, e.g., from mini-black hole production.Comment: 7 pages, presented at Neutrinos and Implications for Physics Beyond the Standard Model, Stony Brook, NY, October 11-13, 200

    Partonic Picture of Nuclear Shadowing at Small x

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    We investigate the nuclear shadowing mechanism in the context of perturbative QCD and the Glauber multiple scattering model. Using recent HERA data on nucleon structure function at small xx, we put stringent constrains on the nucleon gluon density in the double-logarithm approximation. We suggest that the scaling violation of the nucleon structure function in the region of small xx and semihard scale Q2Q^2 can be reliably described by perturbative QCD which is a central key to the understanding of the scale dependence of the nuclear shadowing effect. Our results indicate that while the shadowing of the quark density arises from an interplay between the ``soft'' and semihard QCD processes, the gluon shadowing is largely driven by a perturbative shadowing mechanism. We demonstrate that the gluon shadowing is a robust phenomenon at large Q2Q^2 and can be unambiguously predicted by perturbative QCD.Comment: 15 two-column pages in RevTeX with 9 eps figure


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    We present results on rapidity and transverse momentum distributions of inclusive charm quark production in hadronic and heavy-ion collisions at RHIC and LHC energies, including the next-to-leading order, O(αs3)O(\alpha_s^3), radiative corrections and the nuclear shadowing effect. We determine the hadronic and the {\it effective} (in-medium) K-factor for the differential and total inclusive charm cross sections. We show that these K-factors have strong pTp_T dependence. We discuss how measurements of charm production at RHIC and LHC can provide valuable information about the gluon density in a nucleus.Comment: LaTex, 4 pages, 2 figs (available on request) Talk presented at Eleventh International Conference on Ultra-Relativistic Nucleus-Nucleus Collisions -- Quark Matter '95, Monterey, CA, January 9-13, 1995

    Update on decaying and annihilating heavy dark matter with the 6-year IceCube HESE data

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    In view of the IceCube's 6-year high-energy starting events (HESE) sample, we revisit the possibility that the updated data may be better explained by a combination of neutrino fluxes from dark matter decay and an isotropic astrophysical power-law than purely by the latter. We find that the combined two-component flux qualitatively improves the fit to the observed data over a purely astrophysical one, and discuss how these updated fits compare against a similar analysis done with the 4-year HESE data. We also update fits involving dark matter decay via multiple channels, without any contribution from the astrophysical flux. We find that a DM-only explanation is not excluded by neutrino data alone. Finally, we also consider the possibility of a signal from dark matter annihilations and perform analogous analyses to the case of decays, commenting on its implications.Comment: 36 pages, 14 figure
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