128 research outputs found
Measuring NUMA effects with the STREAM benchmark
Modern high-end machines feature multiple processor packages, each of which
contains multiple independent cores and integrated memory controllers connected
directly to dedicated physical RAM. These packages are connected via a shared
bus, creating a system with a heterogeneous memory hierarchy. Since this shared
bus has less bandwidth than the sum of the links to memory, aggregate memory
bandwidth is higher when parallel threads all access memory local to their
processor package than when they access memory attached to a remote package.
But, the impact of this heterogeneous memory architecture is not easily
understood from vendor benchmarks. Even where these measurements are available,
they provide only best-case memory throughput. This work presents a series of
modifications to the well-known STREAM benchmark to measure the effects of NUMA
on both a 48-core AMD Opteron machine and a 32-core Intel Xeon machine
Spectral Gamma-ray Signatures of Cosmological Dark Matter Annihilation
We propose a new signature for weakly interacting massive particle (WIMP)
dark matter, a spectral feature in the diffuse extragalactic gamma-ray
radiation. This feature, a sudden drop of the gamma-ray intensity at an energy
corresponding to the WIMP mass, comes from the asymmetric distortion of the
line due to WIMP annihilation into two gamma-rays caused by the cosmological
redshift. Unlike other proposed searches for a line signal, this method is not
very sensitive to the exact dark matter density distribution in halos and
subhalos. The only requirement is that the mass distribution of substructure on
small scales follows approximately the Press-Schechter law, and that smaller
halos are on the average denser than large halos, which is a generic outcome of
N-body simulations of Cold Dark Matter, and which has observational support.
The upcoming Gamma-ray Large Area Space Telescope (GLAST) will be eminently
suited to search for these spectral features. For numerical examples, we use
rates computed for supersymmetric particle dark matter, where a detectable
signal is possible.Comment: 4 pages, 1 figure. Matches the published version. Conclusions
unchange
Gamma Rays from Heavy Neutralino Dark Matter
We consider the gamma-ray spectrum from neutralino dark matter annihilations
and show that internal bremsstrahlung of W pair final states gives a previously
neglected source of photons at energies near the mass of the neutralino. For
masses larger than about 1 TeV, and for present day detector resolutions, this
results in a characteristic signal that may dominate not only over the
continuous spectrum from W fragmentation, but also over the \gamma-\gamma and
\gamma-Z line signals which are known to give large rates for heavy
neutralinos. Observational prospects thus seem promising.Comment: 4 pages, 4 figures; revised to match published versio
Indirect detection of dark matter in km-size neutrino telescopes
Journal ArticleNeutrino telescopes of kilometer size are currently being planned. They will be two or three orders of magnitude bigger than presently operating detectors, but they will have a much higher muon energy threshold. We discuss the trade-off between area and energy threshold for indirect detection of neutralino dark matter captured in the Sun and in the Earth and annihilating into high energy neutrinos. We also study the effect of a higher threshold on the complementarity of different searches for supersymmetric dark matter
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