Papers by Orlando Oliveira
Proceedings of The XXV International Symposium on Lattice Field Theory — PoS(LATTICE 2007), 2008
Geophysical Journal International, 2004
We present an exploratory study of a one-parameter family of covariant, non-perturbative lattice ... more We present an exploratory study of a one-parameter family of covariant, non-perturbative lattice gauge-fixing conditions, that can be implemented through a simple Monte Carlo algorithm. We demonstrate that at the numerical level the procedure is feasible, and as a first application we examine the gauge dependence of the gluon propagator.
Either by solving the ghost propagator DSE or through a one-loop computation in the RGZ (Refined ... more 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. UHU-FP/12-010 1
arXiv: High Energy Physics - Theory, 2018
In this work, we report on the possibility of occurrence of oscillon configurations in the fourth... more 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.
Chaos: An Interdisciplinary Journal of Nonlinear Science, 2019
Oscillons are time-dependent, localized in space, extremely long-lived states in nonlinear scalar... more 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 in condensed matter, cosmology, and high-energy physics.
Proceedings of Light Cone 2010: Relativistic Hadronic and Particle Physics — PoS(LC2010), 2010
During recent years, a good agreement was found between the analytical derivation and the numeric... more 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).
Proceedings of XXIIIrd International Symposium on Lattice Field Theory — PoS(LAT2005), 2005
We report on a preliminary study of the volume dependence of the gluon propagator. The propagator... more We report on a preliminary study of the volume dependence of the gluon propagator. The propagator is computed using different lattice volumes, its extrapolation to infinite volume is investigated with particular attention to the its IR behaviour. Our data shows a mild but measurable dependence with the volume. Unfortunately, we are not able yet to clarify its behaviour close to zero momentum.
Proceedings of The many faces of QCD — PoS(FacesQCD), 2011
The calculation of the Landau gauge gluon propagator performed in Coimbra using lattice QCD simul... more 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. The many faces of QCD November 2-5, 2010 Gent Belgium * Speaker.
Brazilian Journal of Physics, 2016
AIP Conference Proceedings, 2007
We report on the infrared limit of the quenched lattice Landau gauge gluon propagator computed fr... more We report on the infrared limit of the quenched lattice Landau gauge gluon propagator computed from large asymmetric lattices. In particular, the compatibility of the pure power law infrared solution (q 2) 2κ of the Dyson-Schwinger equations is investigated and the exponent κ is measured. Some results for the ghost propagator and for the running coupling constant will also be shown.
AIP Conference Proceedings, 2011
The infrared behaviour of the lattice Landau gauge gluon propagator is discussed, combining resul... more 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.
AIP Conference Proceedings, 2012
We develop a model for visible matter-dark matter interaction based on the exchange of a massive ... more 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.
Physical Review B, 2013
The honeycomb carbon structure of graphene and nanotubes has a dynamics which can give rise to a ... more 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.
Physical Review D, 2012
Either by solving the ghost propagator DSE or through a one-loop computation in the RGZ (Refined ... more 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.
Physical Review B, 2011
Effective quantum field theoretical continuum models for graphene are investigated. The models in... more 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 finiteenergy 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.
Physical Review B, 2011
We show that the assumption of a nontrivial zero band gap for a graphene sheet within an effectiv... more 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.
Nuclear Physics B - Proceedings Supplements, 2002
We address the problem of the gauge fixing versus Gribov copies in lattice gauge theories. For th... more We address the problem of the gauge fixing versus Gribov copies in lattice gauge theories. For the Landau gauge, results show that a suitable combination of evolutionary algorithms with traditional steepest descent methods identifies the global maximum of the optimisation function. We discuss the performance of the combined algorithm on small cubic lattices for SU(2) and SU(3).
Journal of Physics: Condensed Matter, 2014
We compute the optical conductivity for an out-of-plane deformation in graphene using an approach... more 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 ∼ 100 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.
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Papers by Orlando Oliveira