Absence of shadowing in Drell-Yan production at finite transverse momentum exchange

Within a perturbative scalar QED model recently considered by Brodsky et al., we study how leading-twist Coulomb rescatterings affect the Drell-Yan cross section at small x = x_{target}, and compare to the case of deep inelastic scattering at small x_{B}. We show that in the range where the transverse momentum transferred to the target is large compared to its minimal value \sim \morder{x}, Coulomb rescatterings affect the DIS cross section but not the Drell-Yan production rate. This illustrates that the leading-twist parton distribution functions become non-universal when cross sections which are differential in target-related particles are considered.Comment: 22 pages, latex, feynm

Comover Enhancement Scenario for Quarkonium Production

The quarkonium data suggest a qualitatively new production mechanism, enhancing the rate of the quarkonia produced in the fragmentation region of an incoming coloured particle.Comment: 6 pages, 1 figure, talk given at DIS 2003, St. Petersburg, 23-27 April 200

Dressing the Quark with QCD Condensates

A condensate of \pvec = 0 partons in the perturbative vacuum gives rise to a term $\propto\delta^4(p)$ in the free PQCD propagators. The leading condensate contribution to the quark propagator can be exactly summed since there is a factor $\delta^4(p)$ associated to each loop. We calculate the dressed quark propagator in the presence of either a gluon or a quark condensate, for a number of colors $N \to \infty$. The dressed quark propagator satisfies a Dyson-Schwinger type equation which can be exactly solved within our framework. In the case of a gluon condensate the dressed quark propagator has no pole, hence quarks cannot appear in asymptotic states, and moreover the DS equation has a solution which spontaneously breaks chiral symmetry. We also calculate the dressed quark-photon vertex and verify that the corresponding Ward-Takahashi identity is satisfied, and that the dressed self-energy correction to the photon propagator does not shift the physical photon pole.Comment: 17 pages, latex, 10 eps figure

QCD Green functions in a gluon field

We formulate a dressed perturbative expansion of QCD, where the standard diagrams are evaluated in the presence of a constant external gluon field whose magnitude is gaussian distributed. The approach is Poincar{\'e} and gauge invariant, and modifies the usual results for hard processes only by power suppressed contributions. Long distance propagation of quarks and gluons turns out to be inhibited due to a branch point singularity instead of a pole at $p^2=0$ in the quark and gluon propagators. The dressing keeps the (massless) quarks in q qbar fluctuations of the photon at a finite distance from each other.Comment: 21 pages, 7 figures. Minor modifications in text. Version to be published in JHE

Medium-induced soft gluon radiation in forward dijet production in relativistic proton-nucleus collisions

International audienceConsidering forward dijet production in the q -> qg partonic process, we derive the spectrum of accompanying soft gluon radiation induced by rescatterings in a nuclear target. The spectrum is obtained to logarithmic accuracy for an arbitrary energy sharing between the final quark and gluon, and for final transverse momenta as well as momentum imbalance being large as compared to transverse momentum nuclear broadening. In the case of equal energy sharing and for approximately back-to-back quark and gluon transverse momenta, we reproduce a previous result of Liou and Mueller. Interpreting our result, we conjecture a simple formula for the medium-induced radiation spectrum associated to hard forward 1 -> n processes, which we explicitly check in the case of the g -> gg process

Intraspecific morphological variation of the middle ear in the European badger, Meles meles (Carnivora: Mustelidae)

International audienc

Valbro : un nouveau site à vertébrés de l’Oligocène inférieur (MP22) de France (Quercy). I – Contexte géologique ; Mammalia : Rodentia, Hyaenodontida, Carnivora

International audienceThe locality Valbro (Quercy, France) has yielded a rich fossil vertebrate fauna. Here are presented the geological context, a preliminary faunal list and the systematics of the Rodentia and carnivores, the most abundant taxa of the fauna. The Rodentia are known from 11 taxa: the Theridomyidae Blainvillimys grega-rius Schlosser, 1884, Blainvillimys ?gemellus Vianey-Liaud, 1989, Issiodoromys medius (Vianey-Liaud, 1976)and S. cayluxi Schlosser, 1884, the Aplodontidae Plesispermophilus angustidens Filhol, 1882, the GliridaeButseloglis tenuis (Bahlo, 1975), Butseloglis micio (Misonne, 1957) and Bransatoglis planus (Bahlo, 1975), theSciuridae Palaeosciurus goti Vianey-Liaud, 1974 and cf. Oligopetes sp., and the Cricetidae Atavocricetodonsp. aff. A. nanus (Pelaez-Campomanes, 1995). Thirteen taxa of carnivores are present at Valbro; amongthe Hyaenodontida: Hyaenodon leptorhynchus Laizer et Parieu, 1838 and cf. Apterodon sp.; among the Car-nivora: a Feliformia gen. et sp. indet., the Nimravidae Nimravus intermedius (Filhol, 1872), Dinailurictisbonali Helbing, 1922 and Nimravidae gen. et sp. indet. (Certainly belonging to one the two already iden-tified species), the Ursida Pachycynodon crassirostris Schlosser, 1888, Pachycynodon sp., Amphicynodonsp. 1 cf. A. typicus (Schlosser, 1888), Amphicynodon ? sp. 2 and Ursida gen. et sp. indet. cf. Pachycynodonboriei (Filhol, 1876), the Mustelida M. olivieri Bonis, 1997, the Carnivora incertae sedis Palaeogale sectoria(Gervais, 1848–1852), the Arctoidea gen. et sp. indet. and Carnivora gen. et sp. indet. (probably represen-ting taxa already identified at lower taxonomic levels). The evolutionary grade of B. gregarius of Valbrocompares to that of the species from Mas de Got, La Plante 2 and Cavalé, which supports an MP22 agefor Valbro. This datation is further supported by the association of Theridomyinae yielded by the locality(B. gregarius, B. gemellus, I. medius and S. cayluxi), and by the presence of a N. intermedius that well comparesthe material of the species from Villebramar, La Plante et Mas de Got, of D. bonali, P. sectoria, M. olivieri(species known only from Mas de Got), and by additional evidence from the remaining vertebrates fromValbro, especially the squamates. Despite a limited amount of specimens (341 specimens have been stu-died), the faunas of rodents and carnivores from Valbro are the most speciose and diverse known for theMP22 level and, for the Carnivora fauna in particular, for the Oligocene of the Old World.Le gisement de Valbro (Quercy, France) a livré une riche faune de vertébrés fossiles. Dans cette contribution sont présentés le contexte géologique, la liste faunique préliminaire et l’étude systématique des rongeurs et des carnassiers, les groupes dominants de cette faune. Les rongeurs sont représentés par 11 taxons : les Theridomyidae Blainvillimys gregarius Schlosser, 1884, Blainvillimys ?gemellus Vianey-Liaud, 1989, Issiodoromys medius (Vianey-Liaud, 1976) et Sciuromys cayluxi Schlosser, 1884,l’Aplodontidae Plesispermophilus angustidens Filhol, 1882, les Gliridae Butseloglis tenuis (Bahlo, 1975),Butseloglis micio (Misonne, 1957) et Bransatoglis planus (Bahlo, 1975), les Sciuridae Palaeosciurusgoti Vianey-Liaud, 1974 et cf. Oligopetes sp., et le Cricetidae Atavocricetodon sp. aff. A. nanus (Pelaez-Campomanes, 1995). Treize taxons de carnassiers sont présents à Valbro ; chez les Hyaenodontida :Hyaenodon leptorhynchus Laizer et Parieu, 1838 et cf. Apterodon sp. ; chez les Carnivora : le Feliformiagen. et sp. indet., les Nimravidae Nimravus intermedius (Filhol, 1872), Dinailurictis bonali Helbing, 1922 etNimravidae gen. et sp. indet. (représentant certainement l’une des deux espèces identifiées), les UrsidaPachycynodon crassirostris Schlosser, 1888, Pachycynodon sp., Amphicynodon sp. 1 cf. A. typicus (Schlosser,1888), Amphicynodon ? sp. 2 et Ursida gen. et sp. indet. cf. Pachycynodon boriei (Filhol, 1876), le Muste-lida Mustelictis olivieri Bonis, 1997, le Carnivora incertae sedis Palaeogale sectoria (Gervais, 1848–1852),l’Arctoidea gen. et sp. indet. et Carnivora gen. et sp. indet. (représentant vraisemblablement un taxon identifié à un rang taxonomique inférieur). Le stade évolutif du B. gregarius de Valbro, comparable à celui de l’espèce provenant de Mas de Got, La Plante 2 et Cavalé rapproche Valbro du niveau MP22 (Oligo-cène inférieur). Cette datation est renforcée par l’association des Theridomyinae rencontrés dans legisement (B. gregarius, B. gemellus, I. medius et S. cayluxi), par la présence d’un N. intermedius au stade évolutif comparable à celui de l’espèce de Villebramar, La Plante et Mas de Got, de D. bonali, P. sectoria,M.olivieri (espèce connue uniquement de Mas de Got), ainsi que par les autres éléments de la faune,notamment les squamates. Malgré un matériel fossile restreint (341 spécimens étudiés), les faunes de rongeurs et de carnassiers de Valbro sont d’une diversité et d’une richesse sans équivalent pour le niveauMP22 et, pour la faune de Carnivora en particulier, sans équivalent pour l’Oligocène de l’Ancien Monde

Une nouvelle faune de vertébrés de la fin de l'Oligocène inférieur à Moissac (Sud-Ouest de la France)

International audienceThe new vertebrate locality Moissac-IV, in SW France, yields the alligatoroid Diplocynodon sp., the turtle Trionyx sp., and a diversified mammal fauna. The mammal assemblage includes the rodent Protechimys cf. lebratierensis, the artiodactyls Caenomeryx sp., Lophiomeryx chalaniati, Gelocus sp., Metriotherium aff. mirabile, Entelodon sp., and Anthracotherium sp., the perissodactyls Protaceratherium albigense and Eggysodon gaudryi, the carnivore Nimravus intermedius. and the creodonts Hyaenodon dubius and Hyaenodon?leptorhynchus. The Moissac-IV fauna, referred to the MP24 reference level, is both totally distinct from those of Moissac-I (MN1, Earliest Miocene) and Moissac-II (MP29, Late Oligocene) and older than Moissac-III (MP26). It provides original data in a stratified context just prior the Early-Late Oligocene transition, i.e. a stratigraphical interval, which for SW France, was essentially documented by karstic fillings of the Phosphorites of Quercy so far. (C) 2011 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved

Testing for Deperet's Rule (Body Size Increase) in Mammals using Combined Extinct and Extant Data

Whether or not evolutionary lineages in general show a tendency to increase in body size has often been discussed. This tendency has been dubbed "Cope's rule" but because Cope never hypothesized it, we suggest renaming it after Deperet, who formulated it clearly in 1907. Deperet's rule has traditionally been studied using fossil data, but more recently a number of studies have used present-day species. While several paleontological studies of Cenozoic placental mammals have found support for increasing body size, most studies of extant placentals have failed to detect such a trend. Here, we present a method to combine information from present-day species with fossil data in a Bayesian phylogenetic framework. We apply the method to body mass estimates of a large number of extant and extinct mammal species, and find strong support for Deperet's rule. The tendency for size increase appears to be driven not by evolution toward larger size in established species, but by processes related to the emergence of new species. Our analysis shows that complementary data from extant and extinct species can greatly improve inference of macroevolutionary processes