56 research outputs found
2PI functional techniques for gauge theories: QED
We discuss the formulation of the prototype gauge field theory, QED, in the
context of two-particle-irreducible (2PI) functional techniques with particular
emphasis on the issues of renormalization and gauge symmetry. We show how to
renormalize all -point vertex functions of the (gauge-fixed) theory at any
approximation order in the 2PI loop-expansion by properly adjusting a finite
set of local counterterms consistent with the underlying gauge symmetry. The
paper is divided in three parts: a self-contained presentation of the main
results and their possible implementation for practical applications; a
detailed analysis of ultraviolet divergences and their removal; a number of
appendices collecting technical details.Comment: 65 pages, 18 figure
2PI effective action for gauge theories: Renormalization
We discuss the application of two-particle-irreducible (2PI) functional
techniques to gauge theories, focusing on the issue of non-perturbative
renormalization. In particular, we show how to renormalize the photon and
fermion propagators of QED obtained from a systematic loop expansion of the 2PI
effective action. At any finite order, this implies introducing new
counterterms as compared to the usual ones in perturbation theory. We show that
these new counterterms are consistent with the 2PI Ward identities and are
systematically of higher order than the approximation order, which guarantees
the convergence of the approximation scheme. Our analysis can be applied to any
theory with linearly realized gauge symmetry. This is for instance the case of
QCD quantized in the background field gauge.Comment: 21 pages, 8 figures. Uses JHEP3.cl
Ward Identities for the 2PI effective action in QED
We study the issue of symmetries and associated Ward-like identities in the
context of two-particle-irreducible (2PI) functional techniques for abelian
gauge theories. In the 2PI framework, the -point proper vertices of the
theory can be obtained in various different ways which, although equivalent in
the exact theory, differ in general at finite approximation order. We derive
generalized (2PI) Ward identities for these various -point functions and
show that such identities are exactly satisfied at any approximation order in
2PI QED. In particular, we show that 2PI-resummed vertex functions, i.e.
field-derivatives of the so-called 2PI-resummed effective action, exactly
satisfy standard Ward identities. We identify another set of -point
functions in the 2PI framework which exactly satisfy the standard Ward
identities at any approximation order. These are obtained as field-derivatives
of the two-point function \bcG^{-1}[\phi], which defines the extremum of the
2PI effective action. We point out that the latter is not constrained by the
underlying symmetry. As a consequence, the well-known fact that the
corresponding gauge-field polarization tensor is not transverse in momentum
space for generic approximations does not constitute a violation of (2PI) Ward
identities. More generally, our analysis demonstrates that approximation
schemes based on 2PI functional techniques respect all the Ward identities
associated with the underlying abelian gauge symmetry. Our results apply to
arbitrary linearly realized global symmetries as well.Comment: 33 pages, 2 figure
Out-of-equilibrium electromagnetic radiation
We derive general formulas for photon and dilepton production rates from an
arbitrary non-equilibrated medium from first principles in quantum field
theory. At lowest order in the electromagnetic coupling constant, these relate
the rates to the unequal-time in-medium photon polarization tensor and
generalize the corresponding expressions for a system in thermodynamic
equilibrium. We formulate the question of electromagnetic radiation in real
time as an initial value problem and consistently describe the virtual
electromagnetic dressing of the initial state. In the limit of slowly evolving
systems, we recover known expressions for the emission rates and work out the
first correction to the static formulas in a systematic gradient expansion.
Finally, we discuss the possible application of recently developed techniques
in non-equilibrium quantum field theory to the problem of electromagnetic
radiation. We argue, in particular, that the two-particle-irreducible (2PI)
effective action formalism provides a powerful resummation scheme for the
description of multiple scattering effects, such as the
Landau-Pomeranchuk-Migdal suppression recently discussed in the context of
equilibrium QCD.Comment: 34 pages, 9 figures, uses JHEP3.cl
Changes in physical activity patterns from adolescence to young adulthood: the BELINDA study
Physical activity (PA) is recognized as a marker of health. The aim was to investigate PA differences from adolescence to young adulthood. European adolescents included in the HELENA study were invited to participate in a follow-up study, 10 years later. The present study included 141 adults (25.0â±â1.4 years) for whom valid accelerometer data were available in adolescence and adulthood. Changes in PA by sex, weight and maternal education level were explored with interactions. Time spent in sedentary activity, light PA (LPA) and moderate PA (MPA) increased by 39.1, 59.6 and 6.6 min/day, respectively, whereas the time spent in vigorous PA (VPA) decreased by 11.3 min/day compared with adolescent VPA (pâ<â0.05). Increases in MPA were greater on weekends compared with weekdays, but we found a greater decrease in VPA on weekdays compared with weekends. Moderate-to-vigorous PA (MVPA) decreased significantly on weekdays (â9.6 min/day; 95%CI, â15.9 to â3.4), while it increased on weekends (8.4 min/day; 95%CI, 1.9 to 14.8). Significant heterogeneity was found across sexes for VPA and MVPA, with a stronger decrease in VPA in males compared with females and a significant decrease in MVPA (â12.5 min/day; 95%CI, â20.4 to â4.5) in males but not in females (1.9 min/day; 95%CI, â5.5 to 9.2). No significant heterogeneity was found to be linked to maternal education level or weight, irrespective of PA level.
Conclusion: Our data suggest that the transition from adolescence to young adulthood is a critical period for lifestyle PA habits. A decline in VPA and an increasingly sedentary time were observed. The observed changes are worrying and may increase the risk of developing adverse health consequences later in life
Optimization of the derivative expansion in the nonperturbative renormalization group
We study the optimization of nonperturbative renormalization group equations
truncated both in fields and derivatives. On the example of the Ising model in
three dimensions, we show that the Principle of Minimal Sensitivity can be
unambiguously implemented at order of the derivative expansion.
This approach allows us to select optimized cut-off functions and to improve
the accuracy of the critical exponents and . The convergence of the
field expansion is also analyzed. We show in particular that its optimization
does not coincide with optimization of the accuracy of the critical exponents.Comment: 13 pages, 9 PS figures, published versio
The genomic basis of color pattern polymorphism in the Harlequin ladybird
© 2018 The Authors Many animal species comprise discrete phenotypic forms. A common example in natural populations of insects is the occurrence of different color patterns, which has motivated a rich body of ecological and genetic research [1â6]. The occurrence of dark, i.e., melanic, forms displaying discrete color patterns is found across multiple taxa, but the underlying genomic basis remains poorly characterized. In numerous ladybird species (Coccinellidae), the spatial arrangement of black and red patches on adult elytra varies wildly within species, forming strikingly different complex color patterns [7, 8]. In the harlequin ladybird, Harmonia axyridis, more than 200 distinct color forms have been described, which classic genetic studies suggest result from allelic variation at a single, unknown, locus [9, 10]. Here, we combined whole-genome sequencing, population-based genome-wide association studies, gene expression, and functional analyses to establish that the transcription factor Pannier controls melanic pattern polymorphism in H. axyridis. We show that pannier is necessary for the formation of melanic elements on the elytra. Allelic variation in pannier leads to protein expression in distinct domains on the elytra and thus determines the distinct color patterns in H. axyridis. Recombination between pannier alleles may be reduced by a highly divergent sequence of âŒ170 kb in the cis-regulatory regions of pannier, with a 50 kb inversion between color forms. This most likely helps maintain the distinct alleles found in natural populations. Thus, we propose that highly variable discrete color forms can arise in natural populations through cis-regulatory allelic variation of a single gene. More than 200 distinct color forms have been described in natural populations of the harlequin ladybird, Harmonia axyridis. Gautier et al. show that this variation is controlled by the transcription factor Pannier. Pannier is necessary to produce black pigment, and its expression pattern prefigures the coloration pattern in each color form
Formation of C-C and C-N bonds catalyzed by Copper, Iron or transition metal-free
Le sujet de cette thĂšse se situe dans le cadre gĂ©nĂ©ral des arylations de nuclĂ©ophiles catalysĂ©es par des complexes de mĂ©taux de transitions (Cu, Fe) ou rĂ©alisĂ©es en absence de ces derniers, dans des conditions compĂ©titives et respectueuses de lâenvironnement. Ces rĂ©actions sont dâune importance majeure pour lâindustrie chimique. Dans un premier chapitre est tout dâabord dĂ©crit un couplage inĂ©dit mettant en jeu un sel dâaryldiazonium et un nuclĂ©ophile azotĂ© (formation de liaison CAr-N). La mĂ©thode procĂšde dans des conditions douces via un systĂšme catalytique au cuivre peu coĂ»teux et peu toxique. Les produits de couplage obtenus (Ar-NHet) sont dâun intĂ©rĂȘt central dans lâindustrie pharmaceutique et agrochimique. Dans une deuxiĂšme partie nous avons prĂ©sentĂ© une mĂ©thode permettant de rĂ©aliser le couplage entre des sels dâaryldiazonium et des dĂ©rivĂ©s du styrĂšne, Ă lâaide dâun systĂšme t BuOK/DMF. Cette rĂ©action, rĂ©alisĂ©e pour la premiĂšre fois en absence de catalyseurs Ă base de mĂ©taux de transition, permet dâaccĂ©der, via la formation de liaisons CArspÂČ-CspÂČ, Ă des motifs stilbĂšnes variĂ©s qui trouvent de nombreuses applications en chimie pharmaceutique. Un deuxiĂšme chapitre porte sur lâutilisation de dĂ©rivĂ©s de lâiode hypervalent permettant la fonctionnalisation de noyaux aromatiques (C-H) ou de dĂ©rivĂ©s vinyliques (C-H). Une premiĂšre mĂ©thode dĂ©crit une rĂ©action de triflimidation directe de composĂ©s acĂ©tanilides avec une sĂ©lectivitĂ© exclusive en position para. Deux conditions rĂ©actionnelles ont Ă©tĂ© mises en place pour cette fonctionnalisation. Une premiĂšre utilise une quantitĂ© stĆchiomĂ©trique de PhI(OAc)2 et une autre utilise une quantitĂ© catalytique dâiodotoluĂšne (gĂ©nĂ©ration in-situ de lâiode(III)). Cette transformation a conduit Ă la formation de liaisons CAr-N en prĂ©sence de bis(trifluoromĂ©thane)sulfonimide de lithium (LINTf2) comme nuclĂ©ophile azotĂ©. Dans une deuxiĂšme partie, nous avons montrĂ© que lâiodure de bisphosphoranilidĂšne (PNPI), pouvait catalyser la trifluoromĂ©thylation vinylique sĂ©lective de dĂ©rivĂ©s du styrĂšne en prĂ©sence dâun rĂ©actif de lâiode hypervalent (lâiode(III)), le rĂ©actif de Togni II. Des travaux sont en cours pour tenter de comprendre lâinfluence positive de lâutilisation de PNPI dans le cas de notre rĂ©action. Un troisiĂšme chapitre dĂ©crit des rĂ©sultats prĂ©liminaires permettant dâobtenir un rendement honorable (54%) lors du couplage catalysĂ© au fer du 4-iodotoluĂšne avec le phĂ©nyllithium. Une autre sĂ©rie de test dĂ©crit le couplage entre des halogĂ©nures dâaryle et des alkyllithium primaires. La mĂ©thode semble trĂšs efficace, puisque par ailleurs les travaux trĂšs rĂ©cents de la littĂ©rature pour des couplages similaires faisant intervenir les mĂȘmes partenaires rĂ©actionnels, font appel Ă des catalyseurs de fer ou de palladium.This thesis is part of a very general search seek to develop methodologies for environmentally sustainable conversion of small molecules into more valuable substances catalyzed by copper and iron complexes or under metal-free conditions. The work focuses on the functionalization of aromatic rings by C-C or C-N bond formation.In a first chapter, a novel coupling involving an aryldiazonium salt and a nitrogenous nucleophile (CAr-N bond formation) is first described. The method proceeds under mild conditions using a cheap and non-toxic copper catalyst system. The obtained coupling products (Ar-NHet) are of central interest in the pharmaceutical and agrochemical industry. Then in a second part, a method allowing the coupling between aryldiazonium salts and styrene derivatives, using a BuOK / DMF system is presented. This reaction, carried out for the first time in the absence of catalysts based on transition metals, makes it possible to access to various stilbene units which find numerous applications in pharmaceutical chemistry.A second chapter concerns the use of hypervalent iodine derivatives allowing the functionalization of aromatic or vinyl substrates. A first method describes a direct triflimidation reaction of acetanilide compounds with an exclusive selectivity in the para position. Two reactions conditions have been established for this functionalization. One uses a stoichiometric amount of PhI(OAc)2 and another uses a catalytic amount of iodotoluene (in-situ generation of iodine (III)). This transformation resulted in the formation of CAr-N bonds in the presence of lithium bis (trifluoromethane) sulfonimide (LINTf2) as the nitrogen nucleophile. In a second part, we have shown that bisphosphoranilidene iodide (PNPI) can catalyze a selective vinylic trifluoromethylation of styrene derivatives in the presence of a hypervalent iodine reagent (iodine (III)), Togniâs reagent II. Work is under way to try to understand the positive influence of PNPI.A third chapter describes preliminary results of an iron-catalyzed heterocoupling of 4-iodotoluene an phenylithium system allowing the obtention of an honorable yield (54%) during the coupling of 4-iodotoluene with phenyllithium. Another series of tests describes the coupling between aryl halides and primary alkyllithiums. The method seems to be very effective, since very recent work in the literature for similar couplings involving the same reaction partners involves catalysts of iron or palladium
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