2,761 research outputs found
Gamma-rays from dark matter annihilations strongly constrain the substructure in halos
Recently, it has been shown that electrons and positrons from dark matter
(DM) annihilations provide an excellent fit to the Fermi, PAMELA, and HESS
data. Using this DM model, which requires an enhancement of the annihilation
cross section over its standard value to match the observations, we show that
it immediately implies an observable level of gamma-ray emission for the Fermi
telescope from nearby galaxy clusters such as Virgo and Fornax. We show that
this DM model implies a peculiar feature from final state radiation that is a
distinctive signature of DM. Using the EGRET upper limit on the gamma-ray
emission from Virgo, we constrain the minimum mass of substructures within DM
halos to be > 5x10^-3 M_sun -- about four orders of magnitudes larger than the
expectation for cold dark matter. This limits the cutoff scale in the linear
matter power spectrum to k < 35/kpc which can be explained by e.g., warm dark
matter. Very near future Fermi observations will strongly constrain the minimum
mass to be > 10^3 M_sun: if the true substructure cutoff is much smaller than
this, the DM interpretation of the Fermi/PAMELA/HESS data must be wrong. To
address the problem of astrophysical foregrounds, we performed high-resolution,
cosmological simulations of galaxy clusters that include realistic cosmic ray
(CR) physics. We compute the dominating gamma-ray emission signal resulting
from hadronic CR interactions and find that it follows a universal spectrum and
spatial distribution. If we neglect the anomalous enhancement factor and assume
standard values for the cross section and minimum subhalo mass, the same model
of DM predicts comparable levels of the gamma-ray emission from DM
annihilations and CR interactions. This suggests that spectral subtraction
techniques could be applied to detect the annihilation signal.Comment: 5 pages, 2 figures (published version; minor corrections to figures
and result, equation added
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
Long Distance Contribution to
We revisit the calculation of the long distance contribution to . We discuss this process within the framework of chiral
perturbation theory, and also using simple models for the vertex. We argue that it is unlikely that this mode can be used to
extract information on short distance parameters. The process
is also long-distance dominated and we find that .Comment: References added, one typo corrected. Version to appear in Nuclear
Physics
Significant Gamma Lines from Inert Higgs Dark Matter
One way to unambiguously confirm the existence of particle dark matter and
determine its mass would be to detect its annihilation into monochromatic
gamma-rays in upcoming telescopes. One of the most minimal models for dark
matter is the inert doublet model, obtained by adding another Higgs doublet
with no direct coupling to fermions. For a mass between 40 and 80 GeV, the
lightest of the new inert Higgs particles can give the correct cosmic abundance
of cold dark matter in agreement with current observations. We show that for
this scalar dark matter candidate, the annihilation signal of monochromatic
\gamma\gamma and Z\gamma final states would be exceptionally strong. The energy
range and rates for these gamma-ray line signals make them ideal to search for
with the soon upcoming GLAST satellite.Comment: 4 pages, 3 figures; minor changes and text improvements; references
updated; published 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
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
Managers' and employees' experiences of how managers' wellbeing impacts their leadership behaviours in Swedish small businesses
BACKGROUND: There is a growing interest in managers' wellbeing due to the observed associations between their wellbeing and leadership behaviours, and between leadership behaviours and employees' wellbeing. However, it is still unclear how managers' wellbeing influences their practiced leadership across different workplace contexts, which specific behaviours are affected, and how this varies across time. OBJECTIVE: The purpose of this study was therefore to explore managers' and employees' experiences and perceptions regarding the consequences of managers' wellbeing for their leadership behaviours in small businesses. METHODS: Semi-structured interviews were conducted with 39 participants (20 managers and 19 employees) working at 12 Swedish small firms, and analysed using content analysis. RESULTS: The findings showthat managers were more constructive when they felt well, and more passively destructive when unwell. Variations in managers' wellbeing influenced their mood, energy level, and performance, as well as the company's working climate. However, these destructive leadership variations did not have a substantial impact, because several protective factors were present. CONCLUSION: This study shows that the wellbeing of managers in small businesses has perceptible consequences for their leadership behaviours. The study also shows that sustained leadership behaviours may coexist with temporary variations of these behaviours on a constructive-destructive continuum depending on the leader's wellbeing. Overall, the findings contribute to a more nuanced and dynamic understanding of how the interaction between managers' wellbeing and their behaviours unfolds in the particular context of small companies
Running mass of the rho0 meson's implication for the dilepton mass spectrum and the mu+mu-/e+e- branching ratio in the K+ --> pi+l+l- decays
We make an attempt to resolve the discrepancy of the observed e+e- mass
spectrum in the K+ --> pi+e+e- decay with that predicted by meson dominance. To
this end we investigate the properties of the rho0 propagator. We use
dispersion relations to evaluate the running mass squared m_rho^2(t) of the
rho0 resonance without adjustable parameters. To improve the convergence of the
dispersion integral, the momentum dependence of strong vertices is taken from
the flux-tube-breaking model of Kokoski and Isgur. The obtained behavior of
m_rho^2(t) at small momentum squared t makes the K+ --> pi+e+e- form factor
rise faster with increasing than in the original meson-dominance
calculation and more in agreement with the published data. As a consequence,
the meson-dominance prediction of the mu+mu-/e+e- branching ratio changes
slightly, from 0.224 to 0.236. We do not see any possibility to accommodate
into the meson-dominance approach an even steeper e+e- spectrum, indicated by
the preliminary data of the E865 collaboration at BNL AGS.Comment: 13 pages, RevTeX, epsf.sty, 4 embedded figure
The public as political consumer - case findings from implementation of organic procurement polices in public food systems in Scandinavia
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
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