3,718 research outputs found
Dark matter annihilation at the galactic center
If cold dark matter is present at the galactic center, as in current models
of the dark halo, it is accreted by the central black hole into a dense spike.
Particle dark matter then annihilates strongly inside the spike, making it a
compact source of photons, electrons, positrons, protons, antiprotons, and
neutrinos. The spike luminosity depends on the density profile of the inner
halo: halos with finite cores have unnoticeable spikes, while halos with inner
cusps may have spikes so bright that the absence of a detected neutrino signal
from the galactic center already places interesting upper limits on the density
slope of the inner halo. Future neutrino telescopes observing the galactic
center could probe the inner structure of the dark halo, or indirectly find the
nature of dark matter.Comment: 4 pages, 5 figure
New Gamma-Ray Contributions to Supersymmetric Dark Matter Annihilation
We compute the electromagnetic radiative corrections to all leading
annihilation processes which may occur in the Galactic dark matter halo, for
dark matter in the framework of supersymmetric extensions of the Standard Model
(MSSM and mSUGRA), and present the results of scans over the parameter space
that is consistent with present observational bounds on the dark matter density
of the Universe. Although these processes have previously been considered in
some special cases by various authors, our new general analysis shows novel
interesting results with large corrections that may be of importance, e.g., for
searches at the soon to be launched GLAST gamma-ray space telescope. In
particular, it is pointed out that regions of parameter space where there is a
near degeneracy between the dark matter neutralino and the tau sleptons,
radiative corrections may boost the gamma-ray yield by up to three or four
orders of magnitude, even for neutralino masses considerably below the TeV
scale, and will enhance the very characteristic signature of dark matter
annihilations, namely a sharp step at the mass of the dark matter particle.
Since this is a particularly interesting region for more constrained mSUGRA
models of supersymmetry, we use an extensive scan over this parameter space to
verify the significance of our findings. We also re-visit the direct
annihilation of neutralinos into photons and point out that, for a considerable
part of the parameter space, internal bremsstrahlung is more important for
indirect dark matter searches than line signals.Comment: Replaced Fig. 2c which by mistake displayed the same spectrum as Fig.
2d; the radiative corrections reported here are now implemented in DarkSUSY
which is available at http://www.physto.se/~edsjo/darksusy
Human resources for control of tuberculosis and HIV-associated tuberculosis.
The global targets for tuberculosis (TB) control were postponed from 2000 to 2005, but on current evidence a further postponement may be necessary. Of the constraints preventing these targets being met, the primary one appears to be the lack of adequately trained and qualified staff. This paper outlines: 1) the human resources and skills for global TB and human immunodeficiency virus (HIV) TB control, including the human resources for implementing the DOTS strategy, the additional human resources for implementing joint HIV-TB control strategies and what is known about human resource gaps at global level; 2) the attempts to quantify human resource gaps by focusing on a small country in sub-Saharan Africa, Malawi; and 3) the main constraints to human resources and their possible solutions, under six main headings: human resource planning; production of human resources; distribution of the work-force; motivation and staff retention; quality of existing staff; and the effect of HIV/AIDS. We recommend an urgent shift in thinking about the human resource paradigm, and exhort international policy makers and the donor community to make a concerted effort to bridge the current gaps by investing for real change
Two photon annihilation of Kaluza-Klein dark matter
We investigate the fermionic one-loop cross section for the two photon
annihilation of Kaluza-Klein (KK) dark matter particles in a model of universal
extra dimensions (UED). This process gives a nearly mono-energetic gamma-ray
line with energy equal to the KK dark matter particle mass. We find that the
cross section is large enough that if a continuum signature is detected, the
energy distribution of gamma-rays should end at the particle mass with a peak
that is visible for an energy resolution of the detector at the percent level.
This would give an unmistakable signature of a dark matter origin of the
gamma-rays, and a unique determination of the dark matter particle mass, which
in the case studied should be around 800 GeV. Unlike the situation for
supersymmetric models where the two-gamma peak may or may not be visible
depending on parameters, this feature seems to be quite robust in UED models,
and should be similar in other models where annihilation into fermions is not
helicity suppressed. The observability of the signal still depends on largely
unknown astrophysical parameters related to the structure of the dark matter
halo. If the dark matter near the galactic center is adiabatically contracted
by the central star cluster, or if the dark matter halo has substructure
surviving tidal effects, prospects for detection look promising.Comment: 17 pages, 3 figures; slightly revised versio
Diffuse inverse Compton and synchrotron emission from dark matter annihilations in galactic satellites
Annihilating dark matter particles produce roughly as much power in electrons
and positrons as in gamma ray photons. The charged particles lose essentially
all of their energy to inverse Compton and synchrotron processes in the
galactic environment. We discuss the diffuse signature of dark matter
annihilations in satellites of the Milky Way (which may be optically dark with
few or no stars), providing a tail of emission trailing the satellite in its
orbit. Inverse Compton processes provide X-rays and gamma rays, and synchrotron
emission at radio wavelengths might be seen. We discuss the possibility of
detecting these signals with current and future observations, in particular
EGRET and GLAST for the gamma rays.Comment: 13 pages, 5 figure
Hemodialysis-associated protein catabolism with and without glucose in the dialysis fluid
Hemodialysis-associated protein catabolism with and without glucose in the dialysis fluid. The effects of hemodialysis on protein and energy metabolism were studied in eight hemodialysis patients. The leg exchange of amino acids (AA) was measured during hemodialysis using a dialysis fluid with 10 mmol/liter glucose (GD) or without glucose (GFD). Arterial AA concentrations decreased by about 30% in GD and GFD. During dialysis, similar increases in the efflux of AA from leg tissues (mainly muscle) were observed in GD and GFD (basal 105 ± 104, vs. 71 ± 62 nmol/min/100 g tissue; dialysis 295 ± 46 vs. 289 ± 60 nmol/min/100 g tissue). The efflux of AA remained largely unchanged at one hour after the end of GD and GFD. Losses of AA to the dialysate were similar during GD (8.3 ± 0.9 g) and GFD (7.9 ± 0.4; NS). GFD resulted in a loss of 26 g of glucose whereas 30 of glucose was absorbed during GD. The amount of urea removed by dialysis and the post-dialysis increase in plasma urea were similar in GD and GFD. In conclusion, the addition of glucose to the dialysis fluid may help the energy balance, but it does not appear to reduce the negative effects of hemodialysis on protein metabolism
Antimatter spectra from a time-dependent modeling of supernova remnants
We calculate the energy spectra of cosmic rays (CR) and their secondaries
produced in a supernova remnant (SNR), taking into account the time-dependence
of the SNR shock. We model the trajectories of charged particles as a random
walk with a prescribed diffusioncoefficient, accelerating the particles at each
shock crossing. Secondary production by CRs colliding with gas is included as a
Monte Carlo process. We find that SNRs produce less antimatter than suggested
previously: The positron/electron ratio and the antiproton/proton ratio are a
few percent and few , respectively. Both ratios do not rise
with energy.Comment: 4 pages, 4 eps figures; v2: results for time-dependent magnetic field
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Indirect signals from light neutralinos in supersymmetric models without gaugino mass unification
We examine indirect signals produced by neutralino self-annihilations, in the
galactic halo or inside celestial bodies, in the frame of an effective MSSM
model without gaugino-mass unification at a grand unification scale. We compare
our theoretical predictions with current experimental data of gamma-rays and
antiprotons in space and of upgoing muons at neutrino telescopes. Results are
presented for a wide range of the neutralino mass, though our discussions are
focused on light neutralinos. We find that only the antiproton signal is
potentially able to set constraints on very low-mass neutralinos, below 20 GeV.
The gamma-ray signal, both from the galactic center and from high galactic
latitudes, requires significantly steep profiles or substantial clumpiness in
order to reach detectable levels. The up-going muon signal is largely below
experimental sensitivities for the neutrino flux coming from the Sun; for the
flux from the Earth an improvement of about one order of magnitude in
experimental sensitivities (with a low energy threshold) can make accessible
neutralino masses close to O, Si and Mg nuclei masses, for which resonant
capture is operative.Comment: 17 pages, 1 tables and 5 figures, typeset with ReVTeX4. The paper may
also be found at http://www.to.infn.it/~fornengo/papers/indirect04.ps.gz or
through http://www.astroparticle.to.infn.it/. Limit from BR(Bs--> mu+ mu-)
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