OPEN CHARM PRODUCTION IN HADRONIC AND HEAVY-ION COLLISIONS AT RHIC AND LHC ENERGIES TO O(αs3)O(\alpha_s^3)

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, $O(\alpha_s^3)$, 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 $p_T$ 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

A streamlined proof of the convergence of the Taylor tower for embeddings in Rn\mathbb R^n

Manifold calculus of functors has in recent years been successfully used in the study of the topology of various spaces of embeddings of one manifold in another. Given a space of embeddings, the theory produces a Taylor tower whose purpose is to approximate this space in a suitable sense. Central to the story are deep theorems about the convergence of this tower. We provide an exposition of the convergence results in the special case of embeddings into $\mathbb R^n$, which has been the case of primary interest in applications. We try to use as little machinery as possible and give several improvements and restatements of existing arguments used in the proofs of the main results.Comment: Minor changes, final versio

Reconciling neutrino flux from heavy dark matter decay and recent events at IceCube

The IceCube detector has recently reported the observation of 28 events at previously unexplored energies. While the statistics of the observed events are still low, these events hint at the existence of a neutrino flux over and above the atmospheric neutrino background. We investigate the possibility that a significant component of the additional neutrino flux originates due to the decay of a very heavy dark matter (VHDM) particle via several possible channels into standard model particles. We show that a combination of a power law astrophysical neutrino spectrum and the neutrino flux from the decay of a DM species of mass in the range $150-400$ TeV improves the fit to the observed neutrino events than that obtained from a best-fit astrophysical flux alone. Assuming the existence of an astrophysical background described by the IC best-fit, we also show that, for the decay of even heavier DM particles ($m_{\text{DM}} \sim 1$ PeV), the same observations impose significant constraints on the decay lifetimes. Allowing the astrophysical flux normalization to vary leads to modifications of these limits, however, there is still a range of dark matter mass and lifetime that is excluded by the IC results.Comment: v1: 8 pages, 2 figures, 2 tables. v2: Minimization over three-parameters (DM mass, lifetime and astrophysical power-law flux normalization); better statistical quantification of fit-goodness; conclusions unchanged; 15 pg, 3 figs, 2 tables; version to appear in JHE

Ultrahigh Energy Neutrinos

The ultrahigh energy neutrino cross section is well understood in the standard model for neutrino energies up to 10$^{12}$ GeV. Test of neutrino oscillations ($\nu_\mu\leftrightarrow\nu_\tau$) from extragalactic sources of neutrinos are possible with large underground detectors. Measurments of horizontal air shower event rates at neutrino energies above 10$^{10}$ 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

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 $x$, 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 $x$ and semihard scale $Q^2$ 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 $Q^2$ and can be unambiguously predicted by perturbative QCD.Comment: 15 two-column pages in RevTeX with 9 eps figure