147 research outputs found
Gamma-ray and Radio Constraints of High Positron Rate Dark Matter Models Annihilating into New Light Particles
The possibility of explaining the positron and electron excess recently found
by the PAMELA and ATIC collaborations in terms of dark matter (DM) annihilation
has attracted considerable attention. Models surviving bounds from, e.g,
antiproton production generally fall into two classes, where either DM
annihilates directly with a large branching fraction into light leptons, or, as
in the recent models of Arkani-Hamed et al., and of Nomura and Thaler, the
annihilation gives low-mass (pseudo)scalars or vectors which then decay
into or . While the constraints on the first kind of
models have recently been treated by several authors, we study here
specifically models of the second type which rely on an efficient Sommerfeld
enhancement in order to obtain the necessary boost in the annihilation cross
section. We compute the photon flux generated by QED radiative corrections to
the decay of and show that this indeed gives a rather spectacular broad
peak in , that for these extreme values of the cross section
violate gamma-ray observations of the Galactic center for DM density profiles
steeper than that of Navarro, Frenk and White. The most stringent constraint
comes from the comparison of the predicted synchrotron radiation in the central
part of the Galaxy with radio observations of Sgr A*. For the most commonly
adopted DM profiles, the models that provide a good fit to the PAMELA and ATIC
data are ruled out, unless there are physical processes that boost the local
anti-matter fluxes more than one order of magnitude, while not affecting the
gamma-ray or radio fluxes.Comment: 5 pages, 3 figures, matches published versio
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
Dark matter interpretation of recent electron and positron data
We analyze the recently released Fermi-LAT data on the sum of electrons and
positrons. Compared to a conventional, pre-Fermi, background model, a
surprising excess in the several hundred GeV range is found and here we analyze
it in terms of dark matter models. We also compare with newly published results
from PAMELA and HESS, and find models giving very good fits to these data sets
as well. If this dark matter interpretation is correct, we also predict the
possibility of a sharp break in the diffuse gamma ray spectrum coming from
final state radiation.Comment: 5 pages, 2 figures, pdflate
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
New Positron Spectral Features from Supersymmetric Dark Matter - a Way to Explain the PAMELA Data?
The space-borne antimatter experiment PAMELA has recently reported a
surprising rise in the positron to electron ratio at high energies. It has also
recently been found that electromagnetic radiative corrections in some cases
may boost the gamma-ray yield from supersymmetric dark matter annihilations in
the galactic halo by up to three or four orders of magnitude, providing
distinct spectral signatures for indirect dark matter searches to look for.
Here, we investigate whether the same type of corrections can also lead to
sizeable enhancements in the positron yield. We find that this is indeed the
case, albeit for a smaller region of parameter space than for gamma rays;
selecting models with a small mass difference between the neutralino and
sleptons, like in the stau coannihilation region in mSUGRA, the effect becomes
more pronounced. The resulting, rather hard positron spectrum with a relatively
sharp cutoff may potentially fit the rising positron ratio measured by the
PAMELA satellite. To do so, however, very large "boost factors" have to be
invoked that are not expected in current models of halo structure. If the
predicted cutoff would also be confirmed by later PAMELA data or upcoming
experiments, one could either assume non-thermal production in the early
universe or non-standard halo formation to explain such a spectral feature as
an effect of dark matter annihilation. At the end of the paper, we briefly
comment on the impact of radiative corrections on other annihilation channels,
in particular antiprotons and neutrinos.Comment: corrected axis labels in Fig. 3; matches the published version (PRD,
in press
Influence of reed beds (Phragmites australis) and submerged vegetation on pike (Esox lucius)
Eutrophication and reduced grazing have led to an expansion of the common reed (Phragmites australis) in ar-chipelago areas in the Baltic Sea, while at the same time the composition of submerged vegetation has changed. Although reed is important as nursery habitat for many fish species, extensive emergent vegetation may reduce biodiversity and abundance of predatory fish. Pike (Esox lucius) is a predatory fish whose larvae and young-of -the-year find both food and shelter in reed but use different micro-habitats during different life-stages. Here we investigate the influence of reed and submerged vegetation on abundance and body size of adult pike during the spawning season. We predicted that coastal bays with extensive but heterogeneous reed beds with higher cover of submerged vegetation would have more and larger pike than bays with smaller, homogenous reed belts or with less submerged vegetation. To test these predictions, we estimated abundance and size-structure of adult pike from catches in angling fishing among 22 bays in the Stockholm archipelago at the Swedish Baltic Sea coast. Our analyses show that catches of adult pike were positively associated with both extensive reed beds and cover of rooted submerged vegetation. However, pike size was not correlated with any vegetation variable, but instead increased with wave exposure and bay area. Our study suggests that reed beds and submerged vegetation are important for adult pike during the spawning season, and even the most extensive reed beds had no evident negative effect on pike populations. We could not see any clear relationship between emergent reed habitat and cover of submerged vegetation among the studied bays, and conclude that to maintain pike population during the spawning season it is important that coastal bays have sufficient amounts of both reed beds and rooted submerged vegetation
Human Astrocytes Transfer Aggregated Alpha-Synuclein via Tunneling Nanotubes.
Many lines of evidence suggest that the Parkinson's disease (PD)-related protein α-synuclein (α-SYN) can propagate from cell to cell in a prion-like manner. However, the cellular mechanisms behind the spreading remain elusive. Here, we show that human astrocytes derived from embryonic stem cells actively transfer aggregated α-SYN to nearby astrocytes via direct contact and tunneling nanotubes (TNTs). Failure in the astrocytes' lysosomal digestion of excess α-SYN oligomers results in α-SYN deposits in the trans-Golgi network followed by endoplasmic reticulum swelling and mitochondrial disturbances. The stressed astrocytes respond by conspicuously sending out TNTs, enabling intercellular transfer of α-SYN to healthy astrocytes, which in return deliver mitochondria, indicating a TNT-mediated rescue mechanism. Using a pharmacological approach to inhibit TNT formation, we abolished the transfer of both α-SYN and mitochondria. Together, our results highlight the role of astrocytes in α-SYN cell-to-cell transfer, identifying possible pathophysiological events in the PD brain that could be of therapeutic relevance.SIGNIFICANCE STATEMENT Astrocytes are the major cell type in the brain, yet their role in Parkinson's disease progression remains elusive. Here, we show that human astrocytes actively transfer aggregated α-synuclein (α-SYN) to healthy astrocytes via direct contact and tunneling nanotubes (TNTs), rather than degrade it. The astrocytes engulf large amounts of oligomeric α-SYN that are subsequently stored in the trans-Golgi network region. The accumulation of α-SYN in the astrocytes affects their lysosomal machinery and induces mitochondrial damage. The stressed astrocytes respond by sending out TNTs, enabling intercellular transfer of α-SYN to healthy astrocytes. Our findings highlight an unexpected role of astrocytes in the propagation of α-SYN pathology via TNTs, revealing astrocytes as a potential target for therapeutic intervention
AGR2, an Endoplasmic Reticulum Protein, Is Secreted into the Gastrointestinal Mucus
The MUC2 mucin is the major constituent of the two mucus layers in colon. Mice lacking the disulfide isomerase-like protein Agr2 have been shown to be more susceptible to colon inflammation. The Agr2(-/-) mice have less filled goblet cells and were now shown to have a poorly developed inner colon mucus layer. We could not show AGR2 covalently bound to recombinant MUC2 N- and C-termini as have previously been suggested. We found relatively high concentrations of Agr2 in secreted mucus throughout the murine gastrointestinal tract, suggesting that Agr2 may play extracellular roles. In tissue culture (CHO-K1) cells, AGR2 is normally not secreted. Replacement of the single Cys in AGR2 with Ser (C81S) allowed secretion, suggesting that modification of this Cys might provide a mechanism for circumventing the KTEL endoplasmic reticulum retention signal. In conclusion, these results suggest that AGR2 has both intracellular and extracellular effects in the intestine
Sun in Stenhagen : designing a solar photovoltaic system at Stenhagen Culture Center
This is a thesis report written as a bachelor’s exam for Uppsala University, Sweden. In this
paper, the possibilities of installing a photovoltaic system on a communal property in Uppsala
is evaluated. Different systems were designed and simulated. It was found that the PV-system
should not be smaller than 150 kWp due to a high self-consumtion-quota for a smaller
system. The shortest payback period was achieved for a 157 kWp system and a 254 kWp
system generates the highest yield after 20 years
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