Search for γ-Ray Line Signals from Dark Matter Annihilations in the Inner Galactic Halo from 10 Years of Observations with H.E.S.S.

Spectral lines are among the most powerful signatures for dark matter (DM) annihilation searches in very-high-energy γ rays. The central region of the Milky Way halo is one of the most promising targets given its large amount of DM and proximity to Earth. We report on a search for a monoenergetic spectral line from self-annihilations of DM particles in the energy range from 300 GeV to 70 TeV using a two-dimensional maximum likelihood method taking advantage of both the spectral and spatial features of the signal versus background. The analysis makes use of Galactic center observations accumulated over ten years (2004-2014) with the H.E.S.S. array of ground-based Cherenkov telescopes. No significant γ-ray excess above the background is found. We derive upper limits on the annihilation cross section ⟨σv⟩ for monoenergetic DM lines at the level of 4×10^{-28} cm^{3} s^{-1} at 1 TeV, assuming an Einasto DM profile for the Milky Way halo. For a DM mass of 1 TeV, they improve over the previous ones by a factor of 6. The present constraints are the strongest obtained so far for DM particles in the mass range 300 GeV-70 TeV. Ground-based γ-ray observations have reached sufficient sensitivity to explore relevant velocity-averaged cross sections for DM annihilation into two γ-ray photons at the level expected from the thermal relic density for TeV DM particles.

H.E.S.S. Limits on Linelike Dark Matter Signatures in the 100 GeV to 2 TeV Energy Range Close to the Galactic Center.

A search for dark matter linelike signals iss performed in the vicinity of the Galactic Center by the H.E.S.S. experiment on observational data taken in 2014. An unbinned likelihood analysis iss developed to improve the sensitivity to linelike signals. The upgraded analysis along with newer data extend the energy coverage of the previous measurement down to 100 GeV. The 18 h of data collected with the H.E.S.S. array allow one to rule out at 95% C.L. the presence of a 130 GeV line (at l=-1.5°, b=0° and for a dark matter profile centered at this location) previously reported in Fermi-LAT data. This new analysis overlaps significantly in energy with previous Fermi-LAT and H.E.S.S. RESULTS: No significant excess associated with dark matter annihilations was found in the energy range of 100 GeV to 2 TeV and upper limits on the gamma-ray flux and the velocity weighted annihilation cross section are derived adopting an Einasto dark matter halo profile. Expected limits for present and future large statistics H.E.S.S. observations are also given.

Search for Dark Matter Annihilations towards the Inner Galactic Halo from 10 Years of Observations with H.E.S.S.

The inner region of the Milky Way halo harbors a large amount of dark matter (DM). Given its proximity, it is one of the most promising targets to look for DM. We report on a search for the annihilations of DM particles using γ-ray observations towards the inner 300 pc of the Milky Way, with the H.E.S.S. array of ground-based Cherenkov telescopes. The analysis is based on a 2D maximum likelihood method using Galactic Center (GC) data accumulated by H.E.S.S. over the last 10 years (2004-2014), and does not show any significant γ-ray signal above background. Assuming Einasto and Navarro-Frenk-White DM density profiles at the GC, we derive upper limits on the annihilation cross section ⟨σv⟩. These constraints are the strongest obtained so far in the TeV DM mass range and improve upon previous limits by a factor 5. For the Einasto profile, the constraints reach ⟨σv⟩ values of 6×10^{-26} cm^{3} s^{-1} in the W^{+}W^{-} channel for a DM particle mass of 1.5 TeV, and 2×10^{-26} cm^{3} s^{-1} in the τ^{+}τ^{-} channel for a 1 TeV mass. For the first time, ground-based γ-ray observations have reached sufficient sensitivity to probe ⟨σv⟩ values expected from the thermal relic density for TeV DM particles.

Constraints on an annihilation signal from a core of constant dark matter density around the milky way center with H.E.S.S.

An annihilation signal of dark matter is searched for from the central region of the Milky Way. Data acquired in dedicated on-off observations of the Galactic center region with H.E.S.S. are analyzed for this purpose. No significant signal is found in a total of ∼9 h of on-off observations. Upper limits on the velocity averaged cross section, ⟨σv⟩, for the annihilation of dark matter particles with masses in the range of ∼300 GeV to ∼10 TeV are derived. In contrast to previous constraints derived from observations of the Galactic center region, the constraints that are derived here apply also under the assumption of a central core of constant dark matter density around the center of the Galaxy. Values of ⟨σv⟩ that are larger than 3×10^{-24} cm^{3}/s are excluded for dark matter particles with masses between ∼1 and ∼4 TeV at 95% C.L. if the radius of the central dark matter density core does not exceed 500 pc. This is the strongest constraint that is derived on ⟨σv⟩ for annihilating TeV mass dark matter without the assumption of a centrally cusped dark matter density distribution in the search region.

Prebiotics in obesity.

Obesity was probably rare in ancient times, with the current increase starting in the Industrial Revolution of the eighteenth century, and becoming much more widespread from about 1950, so concurrent with the increased consumption of carbohydrates from cereals in the Green Revolution. However, dietary components such as oligosaccharides from plants including cereals may improve health following fermentation to short-chain carboxylic acids in the intestine by bacteria which constitute of the microbiome. Such non-digestible and fermentable components of diet, called prebiotics, have been part of the human diet since at least Palaeolithic times, and include components of the cereals domesticated in the Neolithic Revolution. If consumption of these cereals has now increased, why is obesity increasing? One reason could be lowered prebiotic intake combined with increased intake of simple sugars, thus changing the bacteria in the microbiome. Processing of food has played an important role in this change of diet composition. Since obesity is a low-grade inflammation, changing the microbiome by increased consumption of simple carbohydrates and saturated fats may lead to obesity via increased systemic inflammation. Conversely, there is now reasonable evidence that increased dietary prebiotic intake decreases inflammation, improves glucose metabolism and decreases obesity. Would widespread increases in prebiotics in the modern diet, so mimicking Palaeolithic or Neolithic nutrition, decrease the incidence and morbidity of obesity in our communities?

Search for photon-linelike signatures from dark matter annihilations with H.E.S.S.

Gamma-ray line signatures can be expected in the very-high-energy (E(γ)>100 GeV) domain due to self-annihilation or decay of dark matter (DM) particles in space. Such a signal would be readily distinguishable from astrophysical γ-ray sources that in most cases produce continuous spectra that span over several orders of magnitude in energy. Using data collected with the H.E.S.S. γ-ray instrument, upper limits on linelike emission are obtained in the energy range between ∼ 500 GeV and ∼ 25 TeV for the central part of the Milky Way halo and for extragalactic observations, complementing recent limits obtained with the Fermi-LAT instrument at lower energies. No statistically significant signal could be found. For monochromatic γ-ray line emission, flux limits of (2 × 10(-7) -2 × 10(-5)) m(-2) s(-1) sr(-1) and (1 × 10(-8) -2 × 10(-6)) m(-2) s(-1)sr(-1) are obtained for the central part of the Milky Way halo and extragalactic observations, respectively. For a DM particle mass of 1 TeV, limits on the velocity-averaged DM annihilation cross section ⟨σv⟩(χχ → γγ) reach ∼ 10(-27) cm(3)s(-1), based on the Einasto parametrization of the Galactic DM halo density profile.

Bacteriochlorophyll-dependent expression of genes for pigment-binding proteins in Rhodobacter capsulatus involves the RegB/RegA two-component system.

Expression of the puf and puc operons, which encode proteins of the photosynthetic apparatus of Rhodobacter capsulatus, is regulated by oxygen. A drop in the oxygen tension in the environment leads to an increase in the levels of puf and puc mRNAs. In strains lacking bacteriochlorophyll (Bchl) due to mutations in bch genes, the rise in puf and puc mRNA levels observed on reduction of oxygen tension is much less pronounced than in wild-type cells, indicating co-regulation of the syntheses of pigments and pigment-binding proteins. Here we show that Bchl synthesis also affects the expression of the bchC gene, which codes for a subunit of bacteriochlorophyll synthase, suggesting an autoregulatory mechanism for the Bchl biosynthetic pathway. Furthermore, our data provide evidence that the RegB/RegA two-component system, which is known to play a central role in oxygen-controlled expression of photosynthesis genes, is also involved in the Bchl-dependent regulation. Mutant strains which do not synthesize RegB or RegA show similar oxygen-dependent puf and puc expression in the presence and absence of Bchl. Our results support the view that the RegB/RegA system can directly or indirectly sense whether Bchl synthesis takes place or not.

In vivo and in vitro analysis of RegA response regulator mutants of Rhodobacter capsulatus.

In the facultative photosynthetic bacterium Rhodobacter capsulatus, the transcription of genes encoding pigment binding proteins is tightly regulated in response to the oxygen partial pressure by the RegB/ RegA two component system. After a shift from high to low oxygen tension, the response regulator RegA enhances transcription of the puf and puc operon coding for the reaction center, light-harvesting complex I (LHI), and LHII proteins. Various regA mutant strains were analyzed in this study. In a RegA deficient strain, activation of puf and puc transcription is severely impaired which consequently leads to the synthesis of only a few photosynthetic complexes. Strains carrying a mutation in the helix-turn-helix domain of RegA or a mutation of the phosphorylation site, Asp63, show a phenotype like the RegA deficient mutant, although the RegA(D63K) mutant protein showed the same DNA binding behavior as the wild type protein. In contrast, the puf and puc mRNAs still reach about 50-70 % of the wild type level after reduction of oxygen tension in strains which synthesize the C-terminal RegA activator domain only or a hybrid protein composed of the RegA activator and the FixJ receiver domain, while both mutant proteins are impaired in DNA binding. Our data suggest that phosphorylation is not required for DNA binding but rather plays a role for efficient initiation of transcription.

Initial events in the degradation of the polycistronic puf mRNA in Rhodobacter capsulatus and consequences for further processing steps.

Individual segments of the polycistronic puf mRNA of Rhodobacter capsulatus exhibit extremely different half-lives contributing to the stoichiometry of light-harvesting and reaction centre complexes of this facultative phototrophic bacterium. While earlier investigations shed light on the processes leading to the degradation of the 2.7 kb pufBALMX mRNA and, consequently, to the formation of the highly stable 0.5 kb pufBA mRNA processing product, we have now investigated the initial events in the degradation of the highly unstable 3.2 kb pufQBALMX primary transcript. Sequence modifications of two putative RNase E recognition sites within the pufQ coding region provide strong evidence that RNase E-mediated cleavage of a sequence at the 3' end of pufQ is involved in rate-limiting cleavage of the primary pufQBALMX transcript in vivo. The putative RNase E recognition sequence at the 5' end of pufQ is cleaved in vitro but does not contribute to rate-limiting cleavage in vivo. Analysis of the decay of puf mRNA segments transcribed from wild-type and mutated puf DNA sequences in R. capsulatus and Escherichia coli reveal that RNase E-mediated cleavage within the pufQ mRNA sequence also affects the stability of the 0.5 kb pufBA processing product. These findings demonstrate that the stability of a certain mRNA segment depends on the pathway of processing of its precursor molecule.

RNase E enzymes from rhodobacter capsulatus and Escherichia coli differ in context- and sequence-dependent in vivo cleavage within the polycistronic puf mRNA.

The 5' pufQ mRNA segment and the pufLMX mRNA segment of Rhodobacter capsulatus exhibit different stabilities. Degradation of both mRNA segments is initiated by RNase E-mediated endonucleolytic cleavage. While Rhodobacter RNase E does not discriminate between the different sequences present around the cleavage sites within pufQ and pufL, Escherichia coli RNase E shows preference for the sequence harboring more A and U residues.

Molecular cloning and expression analysis of the Rhodobacter capsulatus sodB gene, encoding an iron superoxide dismutase.

Genetic complementation of a sodA sodB Escherichia coli mutant strain was used to clone Rhodobacter capsulatus genes involved in detoxification of superoxide radicals. After sequence analysis, 1 of the 16 identical clones obtained by this selection procedure was shown to contain an open reading frame with sequence similarity to that coding for Fe-containing superoxide dismutases (SodB). The R. capsulatus sodB gene was expressed in E. coli, and the nature of the metal ligand was confirmed by inhibitor sensitivity assays with lysates from both bacterial species. Activity staining of cleared Rhodobacter lysates resolved by polyacrylamide gel electrophoresis indicated that SodB was the only superoxide dismutase present in this phototrophic organism. The sodB gene was expressed at low levels in R. capsulatus cells grown under anaerobic or semiaerobic conditions, but expression was strongly induced upon exposure of the bacteria to air or to methyl viologen. Attempts to construct a sodB mutant in this organism by allelic exchange of the chromosomal copy of the gene with a suicide plasmid containing a mutated sodB gene were unsuccessful, strongly suggesting that the encoded superoxide dismutase is essential for viability of R. capsulatus in aerobic cultures.

Chromosomal location of three wheat sequences with homology to pollen allergen encoding, DNA replication regulating, and DNA (cytosine-5)-methyltransferase genes in wheat and rye.

Three wheat sequences, shown to be homologous to pollen allergen encoding, DNA replication regulating, and DNA (cytosine-5)-methyltransferase genes were localized on chromosomes using nullisomic-tetrasomic wheat ('Chinese Spring') and wheat-rye ('Chinese Spring'/'Imperial') addition lines. Whereas the loci for the pollen allergen encoding sequence (Tri a III) were shown to be located on homoeologous group 4, the DNA replication regulating (Rep) and DNA (cytosine-5)-methyltransferase (Mtase) genes were located to homoeologous groups 1 and 7, respectively, of Triticeae. Chromosomal rearrangements in wheat and rye relative to each other are discussed.