18,040 research outputs found
Nonabelian Faddeev-Niemi Decomposition of the SU(3) Yang-Mills Theory
Faddeev and Niemi (FN) have introduced an abelian gauge theory which
simulates dynamical abelianization in Yang-Mills theory (YM). It contains both
YM instantons and Wu-Yang monopoles and appears to be able to describe the
confining phase. Motivated by the meson degeneracy problem in dynamical
abelianization models, in this note we present a generalization of the FN
theory. We first generalize the Cho connection to dynamical symmetry breaking
pattern SU(N+1) -> U(N), and subsequently try to complete the Faddeev-Niemi
decomposition by keeping the missing degrees of freedom. While it is not
possible to write an on-shell complete FN decomposition, in the case of SU(3)
theory of physical interest we find an off-shell complete decomposition for
SU(3) -> U(2) which amounts to partial gauge fixing, generalizing naturally the
result found by Faddeev and Niemi for the abelian scenario SU(N+1) -> U(1)^N.
We discuss general topological aspects of these breakings, demonstrating for
example that the FN knot solitons never exist when the unbroken gauge symmetry
is nonabelian, and recovering the usual no-go theorems for colored dyons.Comment: Latex 30 page
Energy loss in perturbative QCD
We review the properties of energetic parton propagation in hot or cold QCD
matter, as obtained in recent works. Advances in understanding the energy loss
- collisional and radiative - are summarized, with emphasis on the latter: it
features very interesting properties which may help to detect the quark-gluon
plasma produced in heavy ion collisions. We describe two different theoretical
approaches, which lead to the same radiated gluon energy spectrum. The case of
a longitudinally expanding QCD plasma is investigated. The energy lost by a jet
with given opening angle is calculated in view of making predictions for the
suppression (quenching) of hard jet production. Phenomenological implications
for the difference between hot and cold matter are discussed. Numerical
estimates of the loss suggest that it may be significantly enhanced in hot
compared to cold matter.Comment: 49 pages latex file with 11 embedded PS figures. Uses ar.sty
(included), one equation revised. submitted to Annual Review of Nuclear and
Particle Scienc
Signal transducer and activator of transcription 2 deficiency is a novel disorder of mitochondrial fission
Defects of mitochondrial dynamics are emerging causes of neurological disease. In two children presenting with severe neurological deterioration following viral infection we identified a novel homozygous STAT2 mutation, c.1836C4A (p.Cys612Ter), using whole exome sequencing. In muscle and fibroblasts from these patients, and a third unrelated STAT2-deficient patient, we observed extremely elongated mitochondria. Western blot analysis revealed absence of the STAT2 protein and that the mitochondrial fission protein DRP1 (encoded by DNM1L) is inactive, as shown by its phosphorylation state. All three patients harboured 15 decreased levels of DRP1 phosphorylated at serine residue 616 (P-DRP1S616), a post-translational modification known to activate DRP1, and increased levels of DRP1 phosphorylated at serine 637 (P-DRP1S637), associated with the inactive state of the DRP1 GTPase. Knockdown of STAT2 in SHSY5Y cells recapitulated the fission defect, with elongated mitochondria and decreased PDRP1 S616 levels. Furthermore the mitochondrial fission defect in patient fibroblasts was rescued following lentiviral transduction with wild-type STAT2 in all three patients, with normalization of mitochondrial length and increased P-DRP1S616 levels. Taken 20 together, these findings implicate STAT2 as a novel regulator of DRP1 phosphorylation at serine 616, and thus of mitochondrial fission, and suggest that there are interactions between immunity and mitochondria. This is the first study to link the innate immune system to mitochondrial dynamics and morphology. We hypothesize that variability in JAK-STAT signalling may contribute to the phenotypic heterogeneity of mitochondrial disease, and may explain why some patients with underlying mitochondrial disease decompensate after seemingly trivial viral infections. Modulating JAK-STAT activity may represent a novel 25 therapeutic avenue for mitochondrial diseases, which remain largely untreatable. This may also be relevant for more common neurodegenerative diseases, including Alzheimerâs, Huntingtonâs and Parkinsonâs diseases, in which abnormalities of mitochondrial morphology have been implicated in disease pathogenesis
Fluctuations of particle ratios as a freeze-out probe
We explain how event-by-event fluctuations of particle ratios can constrain
and falsify the statistical model of particle production in heavy ion
collisions, using fluctuations as an example. We define an observable
capable of determining which statistical model, if any, governs freeze-out in
ultrarelativistic heavy ion collisions. We calculate this observable for
fluctuations, and show that it should be the same for RHIC and LHC
energies, as well as independent of centrality, if the Grand-Canonical
statistical model is an appropriate description and chemical equilibrium
applies. We describe what happens in case of deviations from this scenario,
such as light quark chemical non-equilibrium, strange quark over-saturation and
local conservation (canonical ensemble) for strange quarks. We also introduce a
similar observable capable, together with the published measurement, of
ascertaining if an interacting hadron gas phase governs the system between
thermal and chemical freeze-out, and of ascertaining its duration and impact on
hadronic chemistryComment: Proceedings for talk given at Strangeness 2007, Levoca, Slovaki
Symmetries of Snyder--de Sitter space and relativistic particle dynamics
We study the deformed conformal-Poincare symmetries consistent with the
Snyder--de Sitter space. A relativistic particle model invariant under these
deformed symmetries is given. This model is used to provide a gauge independent
derivation of the Snyder--de Sitter algebra. Our results are valid in the
leading order in the parameters appearing in the model.Comment: 12 pages, LaTeX, version appearing in JHEP, minor changes to match
published versio
Structures of Malcev Bialgebras on a simple non-Lie Malcev algebra
Lie bialgebras were introduced by Drinfeld in studying the solutions to the
classical Yang-Baxter equation. The definition of a bialgebra in the sense of
Drinfeld (D-bialgebra), related with any variety of algebras, was given by
Zhelyabin. In this work, we consider Malcev bialgebras. We describe all
structures of a Malcev bialgebra on a simple non-Lie Malcev algebra
q-Deformed quaternions and su(2) instantons
We have recently introduced the notion of a q-quaternion bialgebra and shown
its strict link with the SO_q(4)-covariant quantum Euclidean space R_q^4.
Adopting the available differential geometric tools on the latter and the
quaternion language we have formulated and found solutions of the
(anti)selfduality equation [instantons and multi-instantons] of a would-be
deformed su(2) Yang-Mills theory on this quantum space. The solutions depend on
some noncommuting parameters, indicating that the moduli space of a complete
theory should be a noncommutative manifold. We summarize these results and add
an explicit comparison between the two SO_q(4)-covariant differential calculi
on R_q^4 and the two 4-dimensional bicovariant differential calculi on the bi-
(resp. Hopf) algebras M_q(2),GL_q(2),SU_q(2), showing that they essentially
coincide.Comment: Latex file, 18 page
Higher Curvature Gravity and the Holographic fluid dual to flat spacetime
Recent works have demonstrated that one can construct a (d+2) dimensional
solution of the vacuum Einstein equations that is dual to a (d+1) dimensional
fluid satisfying the incompressible Navier-Stokes equations. In one important
example, the fluid lives on a fixed timelike surface in the flat Rindler
spacetime associated with an accelerated observer. In this paper, we show that
the shear viscosity to entropy density ratio of the fluid takes the universal
value 1/4\pi in a wide class of higher curvature generalizations to Einstein
gravity. Unlike the fluid dual to asymptotically anti-de Sitter spacetimes,
here the choice of gravitational dynamics only affects the second order
transport coefficients. We explicitly calculate these in five-dimensional
Einstein-Gauss-Bonnet gravity and discuss the implications of our results.Comment: 13 pages; v2: modified abstract, added references; v3: added
clarifying comments, modified discussio
Development and Characterization of Curcumin-Silver Nanoparticles as a Promising Formulation to Test on Human Pterygium-Derived Keratinocytes
Pterygium is a progressive disease of the human eye arising from sub-conjunctival tissue and extending onto the cornea. Due to its invasive growth, pterygium can reach the pupil compromising visual function. Currently available medical treatments have limited success in suppressing efficiently the disease. Previous studies have demonstrated that curcumin, polyphenol isolated from the rhizome of Curcuma longa, induces apoptosis of human pterygium fibroblasts in a dose- and time-dependent manner showing promising activity in the treatment of this ophthalmic disease. However, this molecule is not very soluble in water in either neutral or acidic pH and is only slightly more soluble in alkaline conditions, while its dissolving in organic solvents drastically reduces its potential use for biomedical applications. A nanoformulation of curcumin stabilized silver nanoparticles (Cur-AgNPs) seems an effective strategy to increase the bioavailability of curcumin without inducing toxic effects. In fact, silver nitrates have been used safely for the treatment of many ophthalmic conditions and diseases for a long time and the concentration of AgNPs in this formulation is quite low. The synthesis of this new compound was achieved through a modified Bettini's method adapted to improve the quality of the product intended for human use. Indeed, the pH of the reaction was changed to 9, the temperature of the reaction was increased from 90 °C to 100 °C and after the synthesis the Cur-AgNPs were dispersed in Borax buffer using a dialysis step to improve the biocompatibility of the formulation. This new compound will be able to deliver both components (curcumin and silver) at the same time to the affected tissue, representing an alternative and a more sophisticated strategy for the treatment of human pterygium. Further in vitro and in vivo assays will be required to validate this formulation
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