132 research outputs found
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 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
( 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 GeV. Test of neutrino
oscillations () from extragalactic sources of
neutrinos are possible with large underground detectors. Measurments of
horizontal air shower event rates at neutrino energies above 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 , 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
and semihard scale 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 and can be unambiguously predicted by perturbative QCD.Comment: 15 two-column pages in RevTeX with 9 eps figure
OPEN CHARM PRODUCTION IN HADRONIC AND HEAVY-ION COLLISIONS AT RHIC AND LHC ENERGIES TO
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, ,
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
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
Charm decay in slow-jet supernovae as the origin of the IceCube ultra-high energy neutrino events
We investigate whether the recent ultra-high energy (UHE) neutrino events
detected at the IceCube neutrino observatory could come from the decay of
charmed mesons produced within the mildly relativistic jets of supernova-like
astrophysical sources. We demonstrate that the excess of neutrinos
observed by IceCube in the energy range 30 TeV--2 PeV can be explained by a
diffuse flux of neutrinos produced in such slow-jet supernovae, using the
values of astrophysical and QCD parameters within the theoretical uncertainties
associated with neutrino production from charmed meson decay in astrophysical
sources. We discuss the theoretical uncertainties inherent in the evaluation of
charm production in high energy hadronic collisions, as well as the
astrophysical uncertainties associated with slow-jet supernova sources. The
proton flux within the source, and therefore also the produced neutrino flux,
is cut off at around a few PeV, when proton cooling processes become dominant
over proton acceleration. This directly explains the sudden drop in event rates
at energies above a few PeV. We incorporate the effect of energy dependence in
the spectrum-weighted charm production cross-section and show that this has a
very significant effect on the shape, magnitude and cut-off energies for the
neutrino flux.Comment: 5 pages, 3 figure
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