9,480 research outputs found

    Decay of flux vacua to nothing

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    We construct instanton solutions describing the decay of flux compactifications of a 6d6d gauge theory by generalizing the Kaluza-Klein bubble of nothing. The surface of the bubble is described by a smooth magnetically charged solitonic brane whose asymptotic flux is precisely that responsible for stabilizing the 4d compactification. We describe several instances of bubble geometries for the various vacua occurring in a 6d6d Einstein-Maxwell theory namely, AdS_4 x S^2, R^{1,3} x S^2, and dS_4 x S^2. Unlike conventional solutions, the bubbles of nothing introduced here occur where a {\em two}-sphere compactification manifold homogeneously degenerates.Comment: 31 pages, 15 figure

    Diversity and Ecology of Diatoms in Northwest of Algeria: case of El-Hammam stream and Estuary of Cheliff River

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    P. 37-52Ecological research on algae from Algeria and in particular on freshwater and estuarine diatoms remains insufficient. The aim of our work is to contribute to the taxonomy and ecology of benthic diatoms from freshwaters and estuaries in Algeria. For this purpose, we studied two sites of water courses in north-western Algeria: El-Hammam stream at Mascara and the estuary of Cheliff river at Mostaganem. Our inventory of benthic diatoms during dry season at the middle of El-Hammam stream during April, June and August 2010 led to the identification of 44 cosmopolitan species, while 30 species occurred at the mouth of Cheliff river. 10 taxa were recorded for the first time in Algeria. Diversity values (Species richness, Shannon's index and Equitability index) for the two study sites are generally medium to low. The results of the 17 diatom-based metrics tested show that ROTT trophic index (TID) and the Trophic Diatom Index (TDI) best mirrored water quality, but a revision of taxa autecological values is requiredS

    Comparison of charge modulations in La1.875_{1.875}Ba0.125_{0.125}CuO4_4 and YBa2_2Cu3_3O6.6_{6.6}

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    A charge modulation has recently been reported in (Y,Nd)Ba2_2Cu3_3O6+x_{6+x} [Ghiringhelli {\em et al.} Science 337, 821 (2013)]. Here we report Cu L3L_3 edge soft x-ray scattering studies comparing the lattice modulation associated with the charge modulation in YBa2_2Cu3_3O6.6_{6.6} with that associated with the well known charge and spin stripe order in La1.875_{1.875}Ba0.125_{0.125}CuO4_4. We find that the correlation length in the CuO2_2 plane is isotropic in both cases, and is 259±9259 \pm 9 \AA for La1.875_{1.875}Ba0.125_{0.125}CuO4_4 and 55±1555 \pm 15 \AA for YBa2_2Cu3_3O6.6_{6.6}. Assuming weak inter-planar correlations of the charge ordering in both compounds, we conclude that the order parameters of the lattice modulations in La1.875_{1.875}Ba0.125_{0.125}CuO4_4 and YBa2_2Cu3_3O6.6_{6.6} are of the same order of magnitude.Comment: 3 pages, 2 figure

    Spatial Curvature Falsifies Eternal Inflation

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    Inflation creates large-scale cosmological density perturbations that are characterized by an isotropic, homogeneous, and Gaussian random distribution about a locally flat background. Even in a flat universe, the spatial curvature measured within one Hubble volume receives contributions from long wavelength perturbations, and will not in general be zero. These same perturbations determine the Cosmic Microwave Background (CMB) temperature fluctuations, which are O(10^-5). Consequently, the low-l multipole moments in the CMB temperature map predict the value of the measured spatial curvature \Omega_k. On this basis we argue that a measurement of |\Omega_k| > 10^-4 would rule out slow-roll eternal inflation in our past with high confidence, while a measurement of \Omega_k < -10^-4 (which is positive curvature, a locally closed universe) rules out false-vacuum eternal inflation as well, at the same confidence level. In other words, negative curvature (a locally open universe) is consistent with false-vacuum eternal inflation but not with slow-roll eternal inflation, and positive curvature falsifies both. Near-future experiments will dramatically extend the sensitivity of \Omega_k measurements and constitute a sharp test of these predictions.Comment: 16+2 pages, 2 figure

    Anisotropic Power-law Inflation

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    We study an inflationary scenario in supergravity model with a gauge kinetic function. We find exact anisotropic power-law inflationary solutions when both the potential function for an inflaton and the gauge kinetic function are exponential type. The dynamical system analysis tells us that the anisotropic power-law inflation is an attractor for a large parameter region.Comment: 14 pages, 1 figure. References added, minor corrections include

    Significant differences in incubation times in sheep infected with bovine spongiform encephalopathy result from variation at codon 141 in the PRNP gene

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    The susceptibility of sheep to prion infection is linked to variation in the PRNP gene, which encodes the prion protein. Common polymorphisms occur at codons 136, 154 and 171. Sheep which are homozygous for the A&lt;sub&gt;136&lt;/sub&gt;R&lt;sub&gt;154&lt;/sub&gt;Q&lt;sub&gt;171&lt;/sub&gt; allele are the most susceptible to bovine spongiform encephalopathy (BSE). The effect of other polymorphisms on BSE susceptibility is unknown. We orally infected ARQ/ARQ Cheviot sheep with equal amounts of BSE brain homogenate and a range of incubation periods was observed. When we segregated sheep according to the amino acid (L or F) encoded at codon 141 of the PRNP gene, the shortest incubation period was observed in LL141 sheep, whilst incubation periods in FF&lt;sub&gt;141&lt;/sub&gt; and LF&lt;sub&gt;141&lt;/sub&gt; sheep were significantly longer. No statistically significant differences existed in the expression of total prion protein or the disease-associated isoform in BSE-infected sheep within each genotype subgroup. This suggested that the amino acid encoded at codon 141 probably affects incubation times through direct effects on protein misfolding rates
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