10,265 research outputs found
Unified description of seagull cancellations and infrared finiteness of gluon propagators
We present a generalized theoretical framework for dealing with the important
issue of dynamical mass generation in Yang-Mills theories, and, in particular,
with the infrared finiteness of the gluon propagators, observed in a multitude
of recent lattice simulations. Our analysis is manifestly gauge-invariant, in
the sense that it preserves the transversality of the gluon self-energy, and
gauge-independent, given that the conclusions do not depend on the choice of
the gauge-fixing parameter within the linear covariant gauges. The central
construction relies crucially on the subtle interplay between the Abelian Ward
identities satisfied by the nonperturbative vertices and a special integral
identity that enforces a vast number of 'seagull cancellations' among the one-
and two-loop dressed diagrams of the gluon Schwinger-Dyson equation. The key
result of these considerations is that the gluon propagator remains rigorously
massless, provided that the vertices do not contain (dynamical) massless poles.
When such poles are incorporated into the vertices, under the pivotal
requirement of respecting the gauge symmetry of the theory, the terms
comprising the Ward identities conspire in such a way as to still enforce the
total annihilation of all quadratic divergences, inducing, at the same time,
residual contributions that account for the saturation of gluon propagators in
the deep infrared.Comment: 40 pages, 7 figures; v2: typos corrected, version matching the
published on
Evidence of ghost suppression in gluon mass dynamics
In this work we study the impact that the ghost sector of pure Yang-Mills
theories may have on the generation of a dynamical gauge boson mass, which
hinges on the appearance of massless poles in the fundamental vertices of the
theory, and the subsequent realization of the well-known Schwinger mechanism.
The process responsible for the formation of such structures is itself
dynamical in nature, and is governed by a set of Bethe-Salpeter type of
integral equations. While in previous studies the presence of massless poles
was assumed to be exclusively associated with the background-gauge three-gluon
vertex, in the present analysis we allow them to appear also in the
corresponding ghost-gluon vertex. The full analysis of the resulting
Bethe-Salpeter system reveals that the contribution of the poles associated
with the ghost-gluon vertex are particularly suppressed, their sole discernible
effect being a slight modification in the running of the gluon mass, for
momenta larger than a few GeV. In addition, we examine the behavior of the
(background-gauge) ghost-gluon vertex in the limit of vanishing ghost momentum,
and derive the corresponding version of Taylor's theorem. These considerations,
together with a suitable Ansatz, permit us the full reconstruction of the pole
sector of the two vertices involved.Comment: 30 pages, 10 figure
Mass Generation And The Problem Of Seagull Divergences
The gluon mass generation is a purely non-perturbative effect, and the natural framework to study it in the continuum are the Schwinger-Dyson equations (SDEs) of the theory. At the level of the SDEs the generation of such a mass is associated with the existence of infrared finite solutions for the gluon propagator. From the theoretical point of view, the dynamical gluon mass generation has been traditionally plagued with seagull divergences. In this work, we will review how such divergences can be eliminated completely by virtue of a characteristic identity, valid in dimensional regularization. As a pedagogical example, we will first discuss in the context of scalar QED how it is possible to eliminate all seagull divergences, by triggering the aforementioned special identity, which enforces the masslessness of the photon. Then, we will discuss what happens in QCD and present an Ansatz for the three gluon vertex, which completely eliminates all seagull divergences and at same time allows for the possibility of a dynamical gluon mass generation.70613th International Workshop on Hadron PhysicsMAR 22-27, 2015Angra dos Reis, BRAZI
Uptake, equilibrium and kinetics studies for the adsorption of 3- pentanone onto four different clays
The effect of clay treatment on remediation of diethylketone contaminated wastewater : uptake, equilibrium and kinetic studies
The ability of four different clays to adsorb diethylketone was investigated in batch experiments aiming to treat wastewater with low solvent concentrations. The adsorption performance in terms of uptake followed the sequence: vermiculite > sepiolite = kaolinite = bentonite, for all the adsorbent doses tested (from 0.1 to 1.5 g) in 150 mL of ketone solution (800 mg/L). The equilibrium data in the batch systems were described by Sips and Dubinin–Raduskevich isotherms. The best fits for bentonite and kaolinite clays were obtained with the Sips isotherm and for sepiolite and vermiculite the best fits were obtained with the Dubinin–Raduskevich model. Kinetic data were described by pseudo-first and pseudo-second order kinetics models. The best fit was obtained for the pseudo-first order model which assumed that the interaction rate was limited only by one process or mechanism on a single class of sorbing sites and that all sites were time dependent. The presence of functional groups on the clay surface that might have interacted with the solvent was confirmed by FTIR. XRD analysis was also performed. This study showed that the tested clays are very effective for the removal of diethylketone from industrial effluents.The authors gratefully acknowledge the financial support by the Fundacao para a Ciencia e Tecnologia, Ministerio da Ciencia e Tecnologia, Portugal. Hugo Figueiredo thanks FCT for a PhD grant (SFRH/28201/BD/2006) and Cristina Quintelas thanks FCT for a Post doctoral grant (SFRH/BPD/32113/2006). The authors would like also to thank to Minas de Barqueiros, S.A., Prof Rui Boaventura (FEUP-Portugal) and Prof Isabel Correia Neves (Dep. Quimica, UM, Portugal) who kindly supplied the clays and to Dr. A.S. Azevedo for collecting the powder diffraction data (Dep. of Earth Sciences, UM, Portugal). Russell Paterson is thanked for language editing
Catalytic reutilization of Cr(VI) biosorption supports
This work reports the application of a biosorbent, Arthrobacter viscosus, to a zeolitic support (FAU zeolites) as a method for the treatment of Cr(VI)-containing solutions that allows the recovery of the Cr-laden
supports as catalysts for liquid-phase oxidation reactions
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