arXiv subjects

O. Oliveira

Publications and source records attributed to O. Oliveira.

At least 19 recordsLinked to original sources

arXiv2025

On the momentum space structure of the quark propagator

The structure of the quark propagator in momentum space is explored taking into account non-perturbative QCD dynamics constraints for the quark spectral densities derived previously. We assume that the scalar and vector component of the quark propagator share a simple pole but not its residuum, together with other structures. Furthermore, a connection between the poles of the quark propagator and the zeros of the quark wave function $Z(p^2)$ is established. Asymptotic scaling laws for the representation of the quark propagator, after removing the shared pole, are also derived. The confrontation of our results with lattice data for the full QCD quark propagator data are in good agreement. Exploring the link with the lattice data and looking at the Bethe-Salpeter vertex and amplitude, in the chiral limit, we are able to provide estimations for these quantities, for $f_π$ and for the shared pole mass. The pole mass reproduces the constituent quark mass used in the quark models.

hep-ph↗

arXiv2024

Lattice determination of the Batalin-Vilkovisky function and the strong running 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.

hep-lat↗

arXiv2019

Creating Oscillons and Oscillating Kinks in Two Scalar Field Theories

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.

hep-th↗

arXiv2019

The Quark-Gluon Vertex and the QCD Infrared Dynamics

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 $γ_μ$ and to the operator $2 \, p_μ+ q_μ$. The higher rank tensor structures provide small contributions to the vertex.

hep-ph↗

arXiv2018

Approximate dual representation for Yang-Mills SU(2) gauge theory

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 $β$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 $2.5 < β< 3$. The mass of the lightest $J^{PC}=0^{++}$ glueball is evaluated and reproduces the results found in the literature.

hep-lat↗

arXiv2018

Oscillons in $ϕ^6$-theories: Possible occurrence in MHD

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 $ϕ^6$ 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.

hep-th↗

arXiv2017

Lattice QCD static potentials of the meson-meson and tetraquark systems computed with both quenched and full QCD

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.

hep-lat↗

arXiv2017

Gluon and Ghost Dynamics from Lattice QCD

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.

hep-lat↗

arXiv2017

Signature of curved QFT effects on the optical properties of deformed graphene: Curved QFT effects on the optical properties of deformed graphene

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 $\cos^2θ$ law and the decrease of the amplitude of the oscillations with the polarization angle $θ$, 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.

cond-mat.mes-hall↗

arXiv2016

Gluons at finite temperature

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.

hep-lat↗

arXiv2016

Gluon Dynamics, Center Symmetry and the deconfinement phase transition in SU(3) pure Yang-Mills theory

The correlations between the modulus of the Polyakov loop, its phase $θ$ 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 $θ= 0$, $\pm \, 2 π/3$. We find that the gluon propagator form factors associated with $θ\approx 0$ differs quantitatively and qualitatively from those associated to $θ\approx \pm \, 2 π/3$. 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 $θ\approx 0$ and $θ\approx \pm \, 2 π/3$ 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.

hep-lat↗

arXiv2015

Quantum Dynamics in Noisy Backgrounds: from sampling to dissipation and fluctuations

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.

quant-ph↗

arXiv2015

Two Dimensional Honeycomb Materials: random fields, dissipation and fluctuations

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 $Γ$ as a function of the Fermi energy $E_F$. The theoretical prediction for $Γ(E_F)$ is compared to the available experimental data for graphene. The good agreement between $Γ_{theo}$ and $Γ_{exp}$ 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.

cond-mat.mes-hall↗

arXiv2015

Quantum Field Theory Approach to the Optical Conductivity of Strained and Deformed Graphene

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.

cond-mat.mtrl-sci↗

arXiv2015

Cosmological and Particle Physics Constraints on a New Non-Abelian SU(3) Gauge Model for Ordinary/Dark Matter Interaction

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: $e^+ + p \rightarrow μ^+ + X$, where $X = Λ$ or $Λ_c$.

hep-ph↗

arXiv2015

The lattice gluon propagator in renormalizable $ξ$ gauges

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

hep-lat↗

arXiv2014

Optical conductivity of curved graphene

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.

cond-mat.mes-hall↗

arXiv2014

Gluon screening mass at finite temperature from Landau gauge gluon propagator in lattice QCD

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 $T$.

hep-lat↗