37,765 research outputs found
Self-T-Dual Brane Cosmology
We show how T-duality can be implemented with brane cosmology. As a result,
we obtain a smooth bouncing cosmology with features similar to the ones of the
pre-Big Bang scenario. Also, by allowing T-duality transformations along the
time-like direction, we find a static solution that displays an interesting
self tuning property.Comment: 3 pages, based on a talk given at the XI Marcel Grossmann Meeting,
Berlin 23-29 July, 200
GPDs at non-zero skewness in ADS/QCD model
We study Generalized Parton Distribution functions (GPDs) usually measured in
hard exclusive processes and encoding information on the three dimensional
partonic structure of hadrons and their spin decomposition, for non zero
skewness within the AdS/QCD formalism. To this aim the canonical scheme to
calculate GPDs at zero skewness has been properly generalized. Furthermore, we
show that the latter quantities, in this non forward regime, are sensitive to
non trivial details of the hadronic light front wave function, such as a kind
of parton correlations usually not accessible in studies of form factors and
GPDs at zero skewness.Comment: 6 pages, 7 figure
"Poppy" yeast
I am old enough to have taken part in the international project to sequence the first eukaryotic genome—that of Saccharomyces cerevisiae—which was released in 1996. Twenty years later, scientists from academic and commercial institutions are now involved in the first wholesale construction of a eukaryotic genome: the Yeast 2.0 Project 1. The construction of whole genomes from scratch is defined as a bottom-up approach in synthetic biology. One of the aims of such work is to reduce genome size and construct a minimal cell factory for industrial applications. These synthetic yeast chromosomes will have unique features to allow scientists to easily reshuffle, eliminate or add new genes 2 in order to engineer cells for efficient production of a desired compound. Synthetic biologists also use a top-down approach to insert functional biological components into natural genomes. This has been used in yeast to produce natural molecules of pharmaceutical value, such as artemisinin acid 3. Currently, many compounds are not chemically synthesized because it is cheaper and more efficient to extract them from plants. The products of synthetic biology could easily replace plants as the source, especially as yeast fermentation is a matter of days, while plants need months or years to grow
A new approach to non-commutative inflation
We propose an inflationary scenario inspired by a recent formulation, in
terms of coherent states, of non-commutative quantum field theory. We consider
the semiclassical Einstein equations, and we exploit the ultraviolet finiteness
of the non-commutative propagator to construct the expectation value of the
energy momentum tensor associated to a generic scalar field. It turns out that
the latter is always finite and dominated by an effective cosmological
constant. By combining this general feature with the intrinsic fuzziness of
spacetime, we show that non-commutativity governs the energy density of the
early Universe in such a way that the strong energy condition is violated.
Thus, there might be a bounce and a subsequent inflationary phase, which does
not need any \emph{ad hoc} scalar field.Comment: Version extended, more discussions and references, section added on
the cosmological constant, matches version accepted on Class. Quantum Gra
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