884 research outputs found
Dark matter search by exclusive studies of X-rays following WIMPs nuclear interactions
It is shown that weakly interacting massive particles (WIMPs), which are
possible cold dark matter candidates, can be studied by exclusive measurements
of X-rays following WIMPs nuclear interactions. Inner-shell atomic electrons
are ionized through WIMP-nuclear interaction, and then mono-energetic X-rays
are emitted when they are filled by outer-shell electrons. The number of
inner-shell holes amounts to as large as one per five nuclear recoils for
K-shell and several per recoil for L-shell in the case of medium heavy target
nuclei interacting with 100-300 GeV WIMPs. Then the K and L X-ray peaks show up
in the 5-50 keV region. Consequently exclusive studies of the X-rays in
coincidence with the nuclear recoils and the ionization electrons are found to
provide excellent opportunities to detect WIMPs such as the Lightest Super
Symmetric Particles (LSP)Comment: 13 pages, 2 table
Can Solar Neutrinos be a Serious Background in Direct Dark Matter Searches?
The coherent contribution of all neutrons in neutrino nucleus scattering due
to the neutral current is examined considering the boron solar neutrinos. These
neutrinos could potentially become a source of background in the future dark
matter searches aiming at nucleon cross sections in the region well below the
few events per ton per year.Comment: 15 pages, 17 eps figure
Direct Wimp Detection in Directional Experiments
The recent WMAP data have confirmed that exotic dark matter together with the
vacuum energy (cosmological constant) dominate in the flat Universe. Thus the
direct dark matter search, consisting of detecting the recoiling nucleus, is
central to particle physics and cosmology. Modern particle theories naturally
provide viable cold dark matter candidates with masses in the GeV-TeV region.
Supersymmetry provides the lightest supersymmetric particle (LSP), theories in
extra dimensions the lightest Kaluza-Klein particle (LKP) etc. In such theories
the expected rates are much lower than the present experimental goals. So one
should exploit characteristic signatures of the reaction, such as the
modulation effect and, in directional experiments, the correlation of the event
rates with the sun's motion.
In standard non directional experiments the modulation is small, less than
two per cent and the location of the maximum depends on the unknown particle's
mass.
In directional experiments, in addition to the forward-backward asymmetry due
to the sun's motion, one expects a larger modulation, which depends on the
direction of observation. We study such effects both in the case of a light and
a heavy target. Furthermore, since it now appears that the planned experiments
will be partly directional, in the sense that they can only detect the line of
the recoiling nucleus, but not the sense of direction on it, we study which of
the above mentioned interesting features, if any, will persist in these less
ambitious experiments.Comment: 22 LaTex pages, 28 figure
Evaluation of HTTP/DASH Adaptation Algorithms on Vehicular Networks
Video streaming currently accounts for the majority of Internet traffic. One
factor that enables video streaming is HTTP Adaptive Streaming (HAS), that
allows the users to stream video using a bit rate that closely matches the
available bandwidth from the server to the client. MPEG Dynamic Adaptive
Streaming over HTTP (DASH) is a widely used standard, that allows the clients
to select the resolution to download based on their own estimations. The
algorithm for determining the next segment in a DASH stream is not partof the
standard, but it is an important factor in the resulting playback quality.
Nowadays vehicles are increasingly equipped with mobile communication devices,
and in-vehicle multimedia entertainment systems. In this paper, we evaluate the
performance of various DASH adaptation algorithms over a vehicular network. We
present detailed simulation results highlighting the advantages and
disadvantages of various adaptation algorithms in delivering video content to
vehicular users, and we show how the different adaptation algorithms perform in
terms of throughput, playback interruption time, and number of interruptions
Some issues related to the direct detection of dark matter
We briefly review some theoretical issues involved in the direct detection of
supersymmetric (SUSY) dark matter. After a brief discussion of the allowed SYSY
parameter space we focus on the determination of the traditional neutralino
detection rates, in experiments which measure the energy of the recoiling
nucleus, such as the coherent and spin induced rates and the dependence of the
rate on the motion of the Earth (modulation effect). Then we examine the novel
features appearing in directional experiments, which detect the recoiling
nucleus in a given direction. Next we estimate the branching ratios for
transitions to accessible excited nuclear levels. Finally we estimate the event
rates leading to the atom ionization and subsequent detection of the outgoing
electrons.Comment: LaTex, 15 pages, 3 PostScript figure
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