275 research outputs found
Trispectrum versus Bispectrum in Single-Field Inflation
In the standard slow-roll inflationary cosmology, quantum fluctuations in a
single field, the inflaton, generate approximately Gaussian primordial density
perturbations. At present, the bispectrum and trispectrum of the density
perturbations have not been observed and the probability distribution for these
perturbations is consistent with Gaussianity. However, Planck satellite data
will bring a new level of precision to bear on this issue, and it is possible
that evidence for non-Gaussian effects in the primordial distribution will be
discovered. One possibility is that a trispectrum will be observed without
evidence for a non-zero bispectrum. It is not difficult for this to occur in
inflationary models where quantum fluctuations in a field other than the
inflaton contribute to the density perturbations. A natural question to ask is
whether such an observation would rule out the standard scenarios. We explore
this issue and find that it is possible to construct single-field models in
which inflaton-generated primordial density perturbations have an observable
trispectrum, but a bispectrum that is too small to be observed by the Planck
satellite. However, an awkward fine tuning seems to be unavoidable.Comment: 15 pages, 3 figures; journal versio
Etude des Hernandiacées : 6(1)-Lignanes et Alcaloïdes de Hernandia guianensis = studies on Hernandiaceae : 6-Lignans and alkaloids of Hernandia guianensis
Studies on the reactivity of a tertiary allylic alcohol in an acetophenonic series, a model for natural products synthesis
The synthesis of benzopyranic simplified analogues of dibenzopyranic natural compounds is described, together with the access to a precursor of a new furobenzopyranic natural product. These natural products have anti-cancer activity. The 1,3-diacetoxy-2-acetyl-4-(3-hydroxy-3-methylbut-1-enyl)benzene synthone is used as a common precursor to these structures
Dynamics of a lattice Universe : the dust approximation in cosmology
We find a solution to Einstein field equations for a regular toroidal lattice of size L with equal masses M at the centre of each cell; this solution is exact at order M/L. Such a solution is convenient to study the dynamics of an assembly of galaxy-like objects. We find that the solution is expanding (or contracting) in exactly the same way as the solution of a FriedmanâLemaĂźtreâRobertsonâWalker Universe with dust having the same average density as our model. This points towards the absence of backreaction in a Universe filled with an infinite number of objects, and this validates the fluid approximation, as far as dynamics is concerned, and at the level of approximation considered in this work
Les chimanines, nouvelles quinoléines substituées en 2, isolées d'une plante bolivienne antiparasitaire : Galipea longiflora
Novel Cytotoxic 4-Phenylfuranocoumarins from Calophyllum dispar
Eight new 4-phenylfuranocoumarins (1â8) have been isolated from the stem bark and the fruits of Calophyllum dispar, together with three known coumarins. The structures of 1â8 were established by means of spectroscopic analysis, including extensive 2D NMR studies. Some of these furanocoumarins exhibited significant cytotoxic activity against KB cells
ortho-Prenylphenol photooxygenation as a straightforward access to ortho-(2-hydroxy-3-methylbut-3-enyl)phenols
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