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A conformal invariant QED-inspired model is solved for a general covariant linear gauge using the Dyson-Schwinger equations for the propagators assuming a pure vector like interaction. The leading corrections to the asymptotic solutions and the exponents, that characterize the corrections to each of the two fermion propagator functions, are computed as a function of the coupling and gauge fixing parameter $\xi$. For the scalar component of the fermion propagator our findings generalizes for linear covariant gauges previous results found in the literature and reproduce the outcome of the perturbative analysis of quenched QED in the Landau gauge. Our solution for the exponent associated with vector component of the fermion propagator is new and, in the weak coupling regime, agrees with the estimation based on the perturbative analysis of quenched QED. Of the two critical exponents describing the conformal limit of the vector interaction, one of them is, in QED, associated with the regime where chiral symmetry is broken dynamically, which demands one mass scale, namely the Miransky scaling. A second mass scale has to be introduced at larger coupling constants and is associated with a change on the nature of the fermion wave function. This provides one example, that it is possible to find two interwoven cycles in Quantum Field Theory, albeit in a truncated framework, as it is known in the quantum few-body problem in the limit of a zero-range interaction.

The Batalin-Vilkovisky function is a central component in the modern formulation of the background field method and the physical applications derived from it. In the present work we report on novel lattice results for this particular quantity, obtained by capitalizing on its equality with the Kugo-Ojima function in the Landau gauge. The results of the lattice simulation are in very good agreement with the predictions derived from a continuum analysis based on the corresponding Schwinger-Dyson equations. In addition, we show that an important relation connecting this function with the ghost propagator is fulfilled rather accurately. With the aid of these results, we carry out the first completely lattice-based determination of the process-independent strong running interaction, employed in a variety of phenomenological studies., Comment: 8 pages, 6 figures

Oscillons are time-dependent, localized in space, extremely long-lived states in nonlinear scalar-field models, while kinks are topological solitons in one spatial dimension. In the present work, we show new classes of oscillons and oscillating kinks in a system of two nonlinearly coupled scalar fields in $1 + 1$ spatiotemporal dimensions. The solutions contain a control parameter, the variation of which produces oscillons and kinks with a flat-top shape. The model finds applications to condensed matter, cosmology, and high-energy physics., Comment: to be published in Chaos

The Dyson-Schwinger quark equation is solved for the quark-gluon vertex using the most recent lattice data available in the Landau gauge for the quark, gluon and ghost propagators, the full set of longitudinal tensor structures in the Ball-Chiu vertex, taking into account a recently derived normalisation for a quark-ghost kernel form factors and the gluon contribution for the tree level quark-gluon vertex identified on a recent study of the lattice soft gluon limit. A solution for the inverse problem is computed after the Tikhonov linear regularisation of the integral equation, that implies solving a modified Dyson-Schwinger equation. We get longitudinal form factors that are strongly enhanced at the infrared region, deviate significantly from the tree level results for quark and gluon momentum below 2 GeV and at higher momentum approach their perturbative values. The computed quark-gluon vertex favours kinematical configurations where the quark momentum $p$ and the gluon momentum $q$ are small and parallel. Further, the quark-gluon vertex is dominated by the form factors associated to the tree level vertex $\gamma_\mu$ and to the operator $2 \, p_\mu + q_\mu$. The higher rank tensor structures provide small contributions to the vertex., Comment: Some rewriting. Version accepted for publication in Eur Phys J C

In this work, we report on the possibility of occurrence of oscillon configurations in the fourth state of matter. Oscillons are extremely long-lived, time-periodic, spatially-localised scalar field structures. Starting from a scalar field theory in 1+1 space-time dimensions, we find out that small-amplitude oscillons can be obtained in the framework of a $\phi^6$ self-interacting potential. A connection between our results and ideal MHD theory is established. Perspectives for a development of the present work are pointed out.

An approximate dual representation for non-Abelian lattice gauge theories in terms of a new set of dynamical variables, the plaquette occupation numbers (PONs) that are natural numbers, is discussed. They are the expansion indices of the local series of the expansion of the Boltzmann factors for every plaquette of the Yang-Mills action. After studying the constraints due to gauge symmetry, the SU(2) gauge theory is solved using Monte Carlo simulations. For a PONs configuration the weight factor is given by Haar-measure integrals over all links whose integrands are products of powers of plaquettes. Herein, updates are limited to changes of the PON at a plaquette or all PONs on a coordinate plane. The Markov chain transition probabilities are computed employing truncated maximal trees and the Metropolis algorithm. The algorithm performance is investigated with different types of updates for the plaquette mean value over a large range of $\beta$s. Using a $12^4$ lattice very good agreement with a conventional heath bath algorithm is found for the strong and weak coupling limits. Deviations from the latter being below 0.1% for $2.5 < \beta < 3$. The mass of the lightest $J^{PC}=0^{++}$ glueball is evaluated and reproduces the results found in the literature.

We revisit the static potential for the $Q Q \bar Q \bar Q$ system using SU(3) lattice simulations, studying both the colour singlets groundstate and first excited state. We consider geometries where the two static quarks and the two anti-quarks are at the corners of rectangles of different sizes. We analyse the transition between a tetraquark system and a two meson system with a two by two correlator matrix. We compare the potentials computed with quenched QCD and with dynamical quarks. We also compare our simulations with the results of previous studies and analyze quantitatively fits of our results with anzatse inspired in the string flip-flop model and in its possible colour excitations., Comment: 24 pages, 17 figures, 14 tables

The Dirac equation in curved space is used to study the optical transmittance of deformed graphene along a given direction. Our theoretical analysis of the available experimental data for the light transmittance suggests that the periodic ripple associated with the out-of-plane deformation observed in unstrained graphene explains the observations. Furthermore, the experimental uniaxial strained graphene for light transmittance show two features, namely the modification of the $\cos^2\theta$ law and the decrease of the amplitude of the oscillations with the polarization angle $\theta$, which can be well accommodated within the theoretical analysis used here and provide further evidence of the validity of using QFT in curved space to understand two dimensional materials.

The gluon propagator is investigated at finite temperature via lattice simulations. In particular, we discuss its interpretation as a massive-type bosonic propagator. Moreover, we compute the corresponding spectral density and study the violation of spectral positivity. Finally, we explore the dependence of the gluon propagator on the phase of the Polyakov loop., Comment: 6 pages, talk presented by P. J. Silva at the Light Cone 2016 Conference, Lisbon, Portugal, 5-8 September 2016

The two point gluon and ghost correlation functions and the three gluon vertex are investigated, in the Landau gauge, using lattice simulations. For the two point functions, we discuss the approach to the continuum limit looking at the dependence on the lattice spacing and volume. The analytical structure of the propagators is also investigated by computing the corresponding spectral functions using an implementation of the Tikhonov regularisation to solve the integral equation. For the three point function we report results when the momentum of one of the gluon lines is set to zero and discuss its implications., Comment: Proceedings of Light Cone 2016, held in Lisbon, September 2016. Minor changes in text. To appear in Few B Sys

The correlations between the modulus of the Polyakov loop, its phase $\theta$ and the Landau gauge gluon propagator at finite temperature are investigated in connection with the center symmetry for pure Yang-Mills SU(3) theory. In the deconfined phase, where the center symmetry is spontaneously broken, the phase of the Polyakov loop per configuration is close to $\theta = 0$, $\pm \, 2 \pi /3$. We find that the gluon propagator form factors associated with $\theta \approx 0$ differs quantitatively and qualitatively from those associated to $\theta \approx \pm \, 2 \pi /3$. This difference between the form factors is a property of the deconfined phase and a sign of the spontaneous breaking of the center symmetry. Furthermore, given that this difference vanishes in the confined phase, it can be used as an order parameter associated to the deconfinement transition. For simulations near the critical temperature $T_c$, the difference between the propagators associated to $\theta \approx 0$ and $\theta \approx \pm \, 2 \pi /3$ allows to classify the configurations as belonging to the confined or deconfined phase. This establishes a selection procedure which has a measurable impact in the gluon form factors. Our results also show that the absence of the selection procedure can be erroneously taken as lattice artifacts., Comment: 17 pages, 12 figures

We investigate the dynamics of a quantum system coupled linearly to Gaussian white noise using functional methods. By performing the integration over the noisy field in the evolution operator, we get an equivalent non-Hermitian Hamiltonian, which evolves the quantum state with a dissipative dynamics. We also show that if the integration over the noisy field is done for the time evolution of the density matrix, a gain contribution from the fluctuations, can be accessed in addition to the loss one from the non-hermitian Hamiltonian dynamics. We illustrate our study by computing analytically the effective non-Hermitian Hamiltonian, which we found to be the complex frequency harmonic oscillator, with a known evolution operator. It leads to space and time localisation, a common feature of noisy quantum systems in general applications.

In this paper, we propose a method to describe the many-body problem of electrons in honeycomb materials via the introduction of random fields which are coupled to the electrons and have a Gaussian distribution. From a one-body approach to the problem, after integrating exactly the contribution of the random fields, one builds a non-hermitian and dissipative effective Hamiltonian with two-body interactions. Our approach introduces besides the usual average over the electron field a second average over the random fields. The interplay of two averages enables the definition of various types of Green's functions which allow the investigation of fluctuation-dissipation characteristics of the interactions that are a manifestation of the many-body problem. In the current work we study only the dissipative term, through the perturbative analysis of the dynamics associated the effective Hamiltonian generated by two different kinds of couplings. For the cases analysed, the eigenstates of the effective Hamiltonian are complex and, therefore, some of the states have a finite life time. Moreover, we also investigate, in the mean field approximation, the most general parity conserving coupling to the random fields and compute the width of charge carriers $\Gamma$ as a function of the Fermi energy $E_F$. The theoretical prediction for $\Gamma (E_F)$ is compared to the available experimental data for graphene. The good agreement between $\Gamma_{theo}$ and $\Gamma_{exp}$ suggests that description of the many-body problem associated to the electrons in honeycomb materials can indeed be done via the introduction of random fields.

The computation of the optical conductivity of strained and deformed graphene is discussed within the framework of quantum field theory in curved spaces. The analytical solutions of the Dirac equation in an arbitrary static background geometry for one dimensional periodic deformations are computed, together with the corresponding Dirac propagator. Analytical expressions are given for the optical conductivity of strained and deformed graphene associated with both intra and interbrand transitions. The special case of small deformations is discussed and the result compared to the prediction of the tight-binding model.

We propose a mirror model for ordinary and dark matter that assumes a new SU(3) gauge group of transformations, as a natural extension of the Standard Model (SM). A close study of big bang nucleosynthesis, baryon asymmetries, cosmic microwave background bounds, galaxy dynamics, together with the Standard Model assumptions, help us to set a limit on the mass and width of the new gauge boson. The cross section for the elastic scattering of a dark proton by an ordinary proton is estimated and compare to the WIMP--nucleon experimental upper bounds. It is observed that all experimental bounds for the various cross sections can be accommodated consistently within the gauge model. We also suggest a way for direct detection of the new gauge boson via one example of a SM forbidden process: $e^+ + p \rightarrow \mu^+ + X$, where $X = \Lambda$ or $\Lambda_c$., Comment: 11 pages, four figures, This paper supercedes arXiv:1108.2723

We study the SU(3) gluon propagator in renormalizable $R_\xi$ gauges implemented on a symmetric lattice with a total volume of (3.25 fm)$^4$ for values of the guage fixing parameter up to $\xi=0.5$. As expected, the longitudinal gluon dressing function stays constant at its tree-level value $\xi$. Similar to the Landau gauge, the transverse $R_\xi$ gauge gluon propagator saturates at a non-vanishing value in the deep infrared for all values of $\xi$ studied. We compare with very recent continuum studies and perform a simple analysis of the found saturation with a dynamically generated effective gluon mass., Comment: 6 pages, 4 figures

We address the interpretation of the Landau gauge gluon propagator at finite temperature as a massive type bosonic propagator. Using pure gauge SU(3) lattice simulations at a fixed lattice volume $\sim(6.5fm)^3$, we compute the electric and magnetic form factors, extract a gluon mass from Yukawa-like fits, and study its temperature dependence. This is relevant both for the Debye screening at high temperature $T$ and for confinement at low $T$., Comment: Version accepted for publication in PRD

We compute the optical conductivity for an out-of-plane deformation in graphene using an approach based on solutions of the Dirac equation in curved space. Different examples of periodic deformations along one direction translates into an enhancement of the optical conductivity peaks in the region of the far and mid infrared frequencies for periodicities $\sim100\,$nm. The width and position of the peaks can be changed by dialling the parameters of the deformation profiles. The enhancement of the optical conductivity is due to intraband transitions and the translational invariance breaking in the geometrically deformed background. Furthemore, we derive an analytical solution of the Dirac equation in a curved space for a general deformation along one spatial direction. For this class of geometries, it is shown that curvature induces an extra phase in the electron wave function, which can also be explored to produce interference devices of the Aharonov-Bohm type.

We investigate the dressed quark-gluon vertex combining two established non-perturbative approaches to QCD: the Dyson-Schwinger equation (DSE) for the quark propagator and lattice-regularized simulations for the quark, gluon and ghost propagators. The vertex is modeled using a generalized Ball-Chiu ansatz parameterized by a single form factor $\tilde X_0$ which effectively represents the quark-ghost scattering kernel. The solution space of the DSE inversion for $\tilde X_0$ is highly degenerate, which can be dealt with by a numerical regularization scheme. We consider two possibilities: (i) linear regularization and (ii) the Maximum Entropy Method. These two numerical approaches yield compatible $\tilde X_0$ functions for the range of momenta where lattice data is available and feature a strong enhancement of the generalized Ball-Chiu vertex for momenta below 1 GeV. Our ansatz for the quark-gluon vertex is then used to solve the quark DSE which yields a mass function in good agreement with lattice simulations and thus provides adequate dynamical chiral symmetry breaking., Comment: 29 pages, 14 figures, JHEP style

The honeycomb carbon structure of graphene and nanotubes has a dynamics which can give rise to a spectrum. This can be excited via the interaction with an external electromagnetic field. In this work, non-linear waves on graphene and nanotubes associated with the carbon structure are investigated using a gauge model. Typical energies are estimated and there scaling with the nanoribbon width investigated. Furthermore, the soliton-photon interaction depends on the incident photon polarization. In particular, we find that the nanoribbon is transparent when the polarization is along the largest length. Relying on the scaling with the width, we suggest a way to experimentally identify the soliton waves in nanoribbons.

In this proceeding, we explain a few steps for an alternative extraction of the spectral density of a two-point function (propagator) based on a discrete set of data points. We present a so-called Tikhonov regularization of this particular inverse problem. We test it on 2 cases: lattice 0++} glueball data and mock gluon data., Comment: 8 pages, 4 figures. Proceedings of Xth Quark Confinement and the Hadron Spectrum, October 8-12, 2012, TUM Campus Garching, Munich, Germany

In the past years a good comprehension of the infrared gluon propagator has been achieved, with a good qualitative agreement between lattice results and Dyson-Schwinger equations. However, lattice simulations have been performed at physical volumes which are close to 20 fm but using a large lattice spacing. The interplay between volume effects and lattice spacing effects has not been investigated. Here we aim to fill this gap and address how the two effects change the gluon propagator in the infrared region. Furthermore, we provide infinite volume extrapolations which take into account the finite volume and finite lattice spacing. We also report on preliminary results for the gluon propagator at finite temperature., Comment: Proceedings of the 30th International Symposium on Lattice Field Theory - Lattice 2012; June 24-29, 2012; Cairns, Australia

The propagator of a physical degree of freedom ought to obey a K\"{a}ll\'{e}n-Lehmann spectral representation, with positive spectral density. The latter quantity is directly related to a cross section based on the optical theorem. The spectral density is a crucial ingredient of a quantum field theory with elementary and bound states, with a direct experimental connection as the masses of the excitations reflect themselves into (continuum) $\delta$-singularities. In usual lattice simulational approaches to the QCD spectrum the spectral density itself is not accessed. The (bound state) masses are extracted from the asymptotic exponential decay of the two-point function. Given the importance of the spectral density, each nonperturbative continuum approach to QCD should be able to adequately describe it or to take into proper account. In this work, we wish to present a first trial in extracting an estimate for the scalar glueball spectral density in SU(3) gluodynamics using lattice gauge theory., Comment: Proceedings of the 30th International Symposium on Lattice Field Theory - Lattice 2012; June 24-29, 2012; Cairns, Australia

We develop a model for visible matter-dark matter interaction based on the exchange of a massive gray boson called herein the Mulato. Our model hinges on the assumption that all known particles in the visible matter have their counterparts in the dark matter. We postulate six families of particles five of which are dark. This leads to the unavoidable postulation of six parallel worlds, the visible one and five invisible worlds. A close study of big bang nucleosynthesis (BBN), baryon asymmetries, cosmic microwave background (CMB) bounds, galaxy dynamics, together with the Standard Model assumptions, help us to set a limit on the mass and width of the new gauge boson. Modification of the statistics underlying the kinetic energy distribution of particles during the BBN is also discussed. The changes in reaction rates during the BBN due to a departure from the Debye-Hueckel electron screening model is also investigated., Comment: Invited talk at the Workshops "CompStar: the physics and astrophysics of compact stars", Tahiti, June 4-8, 2012, "New Directions in Nuclear Astrophysics", Castiglion Fiorentino, Italy, June 18-22, 2012, and "Carpathian Summer School of Physics", Sinaia, Romania, June 24 - July 7, 2012. To be published in AIP Proceedings

We investigate the phase diagram of the so-called Polyakov--Nambu--Jona-Lasinio (PNJL) model at finite temperature and nonzero chemical potential. The calculations are performed in the light and strange quark sectors ($u$, $d$, $s$), which includes the 't Hooft instanton induced interaction term that breaks the axial symmetry, and the quarks are coupled to the (spatially constant) temporal background gauge field. On one hand, a special attention is payed to the critical end point (CEP). The strength of the flavor-mixing interaction alters the CEP location, since when it becomes weaker the CEP moves to low temperatures and can even disappear. On the other hand, we also explore the connection between QCD, a nonlocal Nambu--Jona-Lasinio type model and the Landau gauge gluon propagator. Possible links between the quenched gluon propagator and low energy hadronic phenomenology are investigated., Comment: Contribution to the International Meeting "Excited QCD", Peniche, Portugal, 06 - 12 May 2012

Either by solving the ghost propagator DSE or through a one-loop computation in the RGZ (Refined Gribov-Zwanziger) formalism, we show that a non-trivial ghost-gluon vertex is anyhow required to obtain a ghost propagator prediction compatible with the available corresponding lattice data in the SU(3) case. For the necessary gluon propagator input, we present RGZ tree level fits which account well for the gluon lattice data. Interestingly, this propagator can be rewritten in terms of a running gluon mass. A comparison of both DSE and RGZ results for the ghost propagator is furthermore provided. We also briefly discuss the connection between the RGZ and the OPE $d=2$ gluon condensate., Comment: 21 pages, 3 figures

In the present work, we investigate how structural defects in graphene can change its transport properties. In particular, we show that breaking of the sublattice symmetry in a graphene monolayer overcomes the Klein effect, leading to confined states of massless Dirac fermions. Experimentally, this corresponds to chemical bonding of foreign atoms to carbon atoms, which attach themselves to preferential positions on one of the two sublattices. In addition, we consider the scattering off a tensor barrier, which describes the rotation of the honeycomb cells of a given region around an axis perpendicular to the graphene layer. We demonstrate that in this case the intervalley mixing between the Dirac points emerges, and that Klein tunneling occurs., Comment: 11 pages, 5 figures

We develop a model for visible matter-dark matter interaction based on the exchange of a weakly interacting massive gauge boson called herein the WIMG. Our model hinges on the assumption that all known particles in the visible matter have their counterparts in the dark matter. We postulate six families of particles five of which are dark. This leads to the unavoidable postulation of six parallel worlds, the visible one and five invisible worlds. We give arguments on particle decays and lifetimes that set a limit on the mass of the WIMG, the gray boson responsible for the very meager communication among these worlds. The 5:1 ratio of dark to visible matter is taken for granted.

A low energy effective field theory model for QCD with a scalar color octet field is discussed. The model relates the gluon mass, the constituent quark masses and the quark condensate. The gluon mass comes about $\sqrt{N_c}\, \Lambda_{QCD}$ with the quark condensate being proportional to the gluon mass squared. The model suggests that the restoration of chiral symmetry and the deconfinement transition occur at the same temperature and that, near the transition, the critical exponent for the condensate is twice the gluon mass one. The model also favors the decoupling like solution for the gluon propagator.

The calculation of the Landau gauge gluon propagator performed in Coimbra using lattice QCD simulations is reviewed. Particular attention is given to the behavior of the gluon propagator in the infrared region and the value of $D(0)$. In the second part of the article, the modeling of the lattice data using massive type propagators and Gribov type propagators is discussed. Four different mass scales are required to describe the propagator over the full range of momenta accessed by the simulations discussed here. Furthermore, assuming a momentum dependent gluon mass, we sketch on its functional dependence., Comment: Contribution to the proceedings of the conference "The many faces of QCD", Gent (Belgium), November 1-5, 2010

Effective quantum field theoretical continuum models for graphene are investigated. The models include a complex scalar field and a vector gauge field. Different gauge theories are considered and their gap patterns for the scalar, vector, and fermion excitations are investigated. Different gauge groups lead to different relations between the gaps, which can be used to experimentally distinguish the gauge theories. In this class of models the fermionic gap is a dynamic quantity. The finite-energy vortex solutions of the gauge models have the flux of the "magnetic field" quantized, making the Bohm-Aharonov effect active even when external electromagnetic fields are absent. The flux comes proportional to the scalar field angular momentum quantum number. The zero modes of the Dirac equation show that the gauge models considered here are compatible with fractionalization.

We show that the assumption of a nontrivial zero band gap for a graphene sheet within an effective relativistic field theoretical model description of interacting Dirac electrons on the surface of graphene describes the experimental band gap of graphene nanoribbons for a wide range of widths. The graphene band gap is dynamically generated, corresponding to a nontrivial gapless solution, found in the limit of an infinitely wide graphene ribbon. The nanoribbon band gap is determined by the experimental graphene work function.

The infrared behaviour of the lattice Landau gauge gluon propagator is discussed, combining results from simulations with different volumes and lattice spacings. In particular, the Cucchieri-Mendes bounds are computed and their implications for D(0) discussed., Comment: 3 pages, 3 figures. Talk given at "Quark Confinement and the Hadron Spectrum IX", Madrid, Spain, August 30th - September 3rd, 2010

The connection between QCD, a nonlocal Nambu--Jona-Lasinio type model and the Landau gauge gluon propagator is explored. This two point function is parameterized by a functional form which is compatible with Dyson-Schwinger and lattice QCD results. Demanding the nonlocal model to reproduce the experimental values for the pion mass, the pion decay constant, $\Gamma_{\pi \rightarrow \gamma\gamma}$ and the light quark condensate we conclude that low energy physics does not distinguish between the so-called decoupling and scaling solutions of the Dyson-Schwinger equations. This result means that, provided that the model parameters are chosen appropriately, one is free to chose any of the above scenarios. Furthermore, the nonlocal Nambu--Jona-Lasinio quark model considered here is chiral invariant and satisfies the GMOR relation at the 1% level of precision., Comment: 12 pages, 4 figures, 2 tables

The gluon and ghost propagators are computed using both quenched and dynamical configurations for the same lattice spacings. The Wilson fermions are simulated at several quark masses. Furthermore, the effect of the Gribov copies is evaluated for all sets of configurations., Comment: 7 pages, 5 figures, poster presented at Lattice 2010 (Vacuum Structure and Confinement)

Over the last years, lattice calculations in pure Yang-Mills gauge theory seem to have come more or less to a consensus. The ghost propagator is not enhanced and the gluon propagator is positivity violating, infrared suppressed and non-vanishing at zero momentum. From an analytical point of view, several groups are agreeing with these results. Among them, the refined Gribov-Zwanziger (RGZ) framework also accommodates for these results. The question which rises next is, if our models hold the right form for the propagators, how to extract information on the real physical observables, i.e. the glueballs? How do the operators which represent glueballs look like? We review the current status of this matter within the RGZ framework., Comment: 3 pages, Conference contribution for Confinement IX, Madrid 2010 (30/08-03/09), to appear in American Institute of Physics (AIP)

The interpretation of the Landau gauge lattice gluon propagator as a massive type bosonic propagator is investigated for i) an infrared constant gluon mass; ii) an ultraviolet constant gluon mass; iii) a momentum dependent mass. We find that the infrared data can be associated with a massive propagator with a constant gluon mass of 651(12) MeV, but the ultraviolet lattice data is not compatible this type of propagator. The scenario of a momentum dependent gluon mass gives a decreasing mass with the momentum, starting from a value of $\sim 630$ MeV in the infrared region and suggesting a $q^2 \ln q^2$ dependence for momenta above 1 GeV., Comment: Contribution to The XXVIII International Symposium on Lattice Field Theory, Lattice2010

During recent years, a good agreement was found between the analytical derivation and the numerical simulation of the Landau gauge gluon and ghost propagators. We mention the Schwinger-Dyson and Gribov-Zwanziger formalism for the analytical work. Although the agreement between several approaches is nice, these propagators do not correspond to the relevant physical degrees of freedom. In the case of pure gauge theories, one should start to study the glueball correlators. We shall try to explain why it looks like a hard challenge to go from the unphysical to the physical propagators in the case of the Gribov-Zwanziger theory (but similar conclusions might hold for other approaches giving similar propagators)., Comment: 10 pages, 3 .eps figures. Talk given by D. Dudal at Light Cone 2010: Relativistic Hadronic and Particle Physics, June 14-18, 2010, Valencia, Spain

The interpretation of the Landau gauge lattice gluon propagator as a massive type bosonic propagator is investigated. Three different scenarios are discussed: i) an infrared constant gluon mass; ii) an ultraviolet constant gluon mass; iii) a momentum dependent mass. We find that the infrared data can be associated with a massive propagator up to momenta $\sim 500$ MeV, with a constant gluon mass of 723(11) MeV, if one excludes the zero momentum gluon propagator from the analysis, or 648(7) MeV, if the zero momentum gluon propagator is included in the data sets. The ultraviolet lattice data is not compatible with a massive type propagator with a constant mass. The scenario of a momentum dependent gluon mass gives a decreasing mass with the momentum, which vanishes in the deep ultraviolet region. Furthermore, we show that the functional forms used to describe the decoupling like solution of the Dyson-Schwinger equations are compatible with the lattice data with similar mass scales., Comment: Version to appear in J. Phys. G. New version include some rewriting and new analysis. In particular, the section on the running mass is new

We consider the gluon propagator $D(p^2)$ at various lattice sizes and spacings in the case of pure SU(3) Yang-Mills gauge theories using the Landau gauge fixing. We discuss a class of fits in the infrared region in order to (in)validate the tree level analytical prediction in terms of the (Refined) Gribov-Zwanziger framework. It turns out that an important role is played by the presence of the widely studied dimension two gluon condensate $\braket{A^2}$. Including this effect allows to obtain an acceptable fit up to 1 \'{a} 1.5 GeV, while corroborating the Refined Gribov-Zwanziger prediction for the gluon propagator. We also discuss the infinite volume extrapolation, leading to the estimate $D(0)=8.3\pm0.5\text{GeV}^{-2}$. As a byproduct, we can also provide the prediction $\braket{g^2 A^2}\approx 3\text{GeV}^2$ obtained at the renormalization scale $\mu=10\text{GeV}$., Comment: 17 pages, 10 figures, updated version, accepted for publication in Phs.Rev.D

he Wu-Yang monopole for pure SU(2) Yang-Mills theory is revisited. New classical solutions with finite energy are found for a generalized Wu-Yang configuration. Our method relies on known asymptotic series solutions and explores the conformal invariance of the theory to set the scale for the monopole configurations. Furthermore, by breaking the scale invariance of the pure Yang-Mills theory by a term which simulates the coupling to quark fields, four different monopole configurations with an energy of 2.9 GeV and spatial extent of 1.2 fm, 1.4 fm, 2.4 fm and 2.6 fm are obtained. These configurations may play a role in the transition to the plasma phase., Comment: The article was considerable expanded, including new sections on numerical solutions, solutions with discontinuous first derivatives and solutions with an explicit breaking of conformal invariance.

In lattice QCD, a confining potential for a static quark-antiquark pair can be computed with the Wilson loop technique. This potential, dominated by a linear potential at moderate distances, is consistent with the confinement with a flux tube, an extended and scalar system also directly observable in lattice QCD. Quantized flux tubes have also been observed in another class of confinement, the magnetic confinement in type II superconductors. On the other hand the solution of Schwinger Dyson Equations, say with the Landau gauge fixing and the truncation of the series of Feynman diagrams, already at the rainbow level for the self energy and at the ladder level for the Bethe Salpeter equation, provides a signal of a possible inverse quartic potential in momentum space derived from one gluon and one ghost exchange, consistent with confinement. Here we address the successes, difficulties and open problems of the matching of these two different perspectives of confinement, the Schwinger-Dyson perspective versus the flux tube perspective., Comment: 12 pages, 18 figures; talk presented at QCD-TNT, Trento, 7-11 sep 2009

The Landau gauge lattice gluon propagator is discussed for different sets of lattices. Particular attention is given to its infrared properties. Our results show that the lattice propagator can be made compatible with either the decoupling-like or the scaling-like solution of the Dyson-Schwinger equations. Furthermore, the analysis of the Cucchieri-Mendes bounds is performed onsidering large volume simulations and the Oliveira-Silva ratios are computed. If the first do not give a clear answer about the value of D(0), the second method favors a $D(0) = 0$. Finally, the SU(3) and SU(2) propagators are compared in the infrared. It comes out that the propagators are different although the infrared exponents seem to be similar. The analysis suggests a scaling behaviour $D(0) \sim N$ with the gauge group SU(N)., Comment: Talk given at International Workshop on QCD Green's Functions, Confinement, and Phenomenology - QCD-TNT09, September 2009, Trento, Italy

We report on the infrared behaviour of the lattice gluon propagator. The bounds on D(0) and their behaviour with the lattice volume are investigated, together with the full propagator. Moreover, a study of the gluon propagator using different lattice spacings is carried out., Comment: 7 pages, 3 figures, talk presented at Lattice 2009 (Vacuum Structure and Confinement)

In this work we calculate the effects of the electroweak flavour changing neutral currents dimension six effective operators on single top production at the LHC. These results are then combined with previous ones we have obtained for the strong sector. This allow us, for the first time, to perform a combined analysis of flavour changing neutral currents in top production with all contributing dimension six operators. Finally, we study the feasibility of their observation and characterization both at the Tevatron and at the LHC., Comment: 16 pages, 13 figures