Analyzing dynamical gluon mass generation

We study the necessary conditions for obtaining infrared finite solutions from the Schwinger-Dyson equation governing the dynamics of the gluon propagator. The equation in question is set up in the Feynman gauge of the background field method, thus capturing a number of desirable features. Most notably, and in contradistinction to the standard formulation, the gluon self-energy is transverse order-by-order in the dressed loop expansion, and separately for gluonic and ghost contributions. Various subtle field-theoretic issues, such as renormalization group invariance and regularization of quadratic divergences, are briefly addressed. The infrared and ultraviolet properties of the obtained solutions are examined in detail, and the allowed range for the effective gluon mass is presented.Comment: 7 pages, 4 figures. Talk presented at "Infrared QCD in Rio" (IRQCD 2006), 5-9 June 2006, Rio de Janeiro, Brazi

Breit-Wigner formalism for non-Abelian theories

The consistent description of resonant transition amplitudes within the framework of perturbative field theories necessitates the definition and resummation of off-shell Green's functions, which must respect several crucial physical requirements. In particular, the generalization of the usual Breit-Wigner formalism in a non-Abelian context constitutes a highly non-trivial problem, related to the fact that the conventionally defined Green's functions are unphysical. We briefly review the main field-theoretical difficulties arising when attempting to use such Green's functions outside the confines of a fixed order perturbative calculation, and explain how this task has been successfully accomplished in the framework of the pinch technique

Dynamics of pollutant discharge in combined sewer systems during rain events: chance or determinism?

International audienceA large database of continuous flow and turbidity measurements cumulating data on hundreds of rain events and dry weather days from two sites in Paris (called Quais and Clichy) and one in Lyon (called Ecully) is presented. This database is used to characterize and compare the behaviour of the three sites at the inter-events scale. The analysis is probed through three various variables: total volumes and total suspended solids (TSS) masses and concentrations during both wet and dry weather periods in addition to the contributions of diverse-origin sources to event flow volume and TSS load values. The results obtained confirm the previous findings regarding the spatial consistency of TSS fluxes and concentrations between both sites in Paris having similar land uses. Moreover, masses and concentrations are proven to be correlated between Parisian sites in a way that implies the possibility of some deterministic processes being reproducible from one catchment to another for a particular rain event. The results also demonstrate the importance of the contribution of wastewater and sewer deposits to the total events' loads and show that such contributions are not specific to Paris sewer networks

Effective gluon mass and infrared fixed point in QCD

We report on a special type of solutions for the gluon propagator of pure QCD, obtained from the corresponding non-linear Schwinger-Dyson equation formulated in the Feynman gauge of the background field method. These solutions reach a finite value in the deep infrared and may be fitted using a massive propagator, with the crucial characteristic that the effective ``mass'' employed depends on the momentum transfer. Specifically, the gluon mass falls off as the inverse square of the momentum, as expected from the operator-product expansion. In addition, one may define a dimensionless quantity, which constitutes the generalization in a non-Abelian context of the universal QED effective charge. This strong effective charge displays asymptotic freedom in the ultraviolet whereas in the low-energy regime it freezes at a finite value, giving rise to an infrared fixed point for QCD.Comment: 6 pages, 2 figures, Talk given at QCD@work 2007, Martina Franca, Italy, 16-20 June 200

Gluon mass generation without seagull divergences

Dynamical gluon mass generation has been traditionally plagued with seagull divergences, and all regularization procedures proposed over the years yield finite but scheme-dependent gluon masses. In this work we show how such divergences can be eliminated completely by virtue of a characteristic identity, valid in dimensional regularization. The ability to trigger the aforementioned identity hinges crucially on the particular Ansatz employed for the three-gluon vertex entering into the Schwinger-Dyson equation governing the gluon propagator. The use of the appropriate three-gluon vertex brings about an additional advantage: one obtains two separate (but coupled) integral equations, one for the effective charge and one for the gluon mass. This system of integral equations has a unique solution, which unambiguously determines these two quantities. Most notably, the effective charge freezes in the infrared, and the gluon mass displays power-law running in the ultraviolet, in agreement with earlier considerations.Comment: 37 pages, 9 figures; minor typos corrected and a few brief explanatory remarks adde

Non-perturbative QCD effective charges

Using gluon and ghost propagators obtained from Schwinger-Dyson equations (SDEs), we construct the non-perturbative effective charge of QCD. We employ two different definitions, which, despite their distinct field-theoretic origin, give rise to qualitative comparable results, by virtue of a crucial non-perturbative identity. Most importantly, the QCD charge obtained with either definition freezes in the deep infrared, in agreement with theoretical and phenomenological expectations. The various theoretical ingredients necessary for this construction are reviewed in detail, and some conceptual subtleties are briefly discussed.Comment: Invited talk at Light Cone 2009: Relativistic Nuclear and Particle Physics (LC2009), Sao Jose dos Campos, Brazil, 8-13 July, 200

Sero-prevalence and serotypes of infectious bronchitis virus in free-range chicken in Plateau state, Nigeria

Globally, infectious bronchitis (IB) is an important respiratory viral disease responsible for enormous economic losses to poultry farmers.  In Nigeria, limited reports on the prevalence and serotypes of the IB virus are available. Here, we investigated the prevalence and serotypes of infectious bronchitis virus (IBV) in chicken in Plateau State. A descriptive cross-sectional study was carried out involving 440 apparently healthy free-range local chickens sampled from eleven villages in four Local Government Areas (LGA) of Plateau State. Sera collected from the birds were screened for the presence of four IBV serotypes namely; Massachusetts (Mass), Arkansas (Ark), Connecticut (Con) and Delaware (De-072) using haemagglutinationinhibition (HI) test. In all, a prevalence of 82.95% (n = 365) was recorded. At LGAlevel, prevalence of 79.50%, 47.37%, 95.45% and 100% were recorded in Kanam, Mangu, Qua’an pan and Bassa LGAs, respectively. Based on serotype prevalence, Mass had 89.30% (n = 326); Ark 79.70% (n = 291); Con 88.20% (n = 322) while De-072 was 42.70% (n = 156). There were statistically significant associations between dominant serotype and the LGAs (p≤0.001). This study shows high prevalence of IBwith at least four strains of IBV present in free-range chicken flocks in Plateau State requiring attention for control measures. Keywords: Free-range chicken; Infectious bronchitis virus; Plateau state, Serosurvey, Serotyp