arXiv subjects

Pedro Bicudo

Publications and source records attributed to Pedro Bicudo.

At least 73 records · Page 4Linked to original sources

arXiv2012

Colour Fields of the Static Pentaquark System Computed in SU(3) Lattice QCD

We compute the colour fields of SU(3) lattice QCD created by static pentaquark systems, in a $24^3\times 48$ lattice at $β=6.2$ corresponding to a lattice spacing $a=0.07261(85)$ fm. We find that the pentaquark colour fields are well described by a multi-Y-type shaped flux tube. The flux tube junction points are compatible with Fermat-Steiner points minimizing the total flux tube length. We also compare the pentaquark flux tube profile with diquark-diantiquark central flux tube profile in the tetraquark and the quark-antiquark fundamental flux tube profile in the meson, and they match, thus showing that the pentaquark flux tubes are composed of fundamental flux tubes.

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arXiv2012

Detailed study of quark-antiquark flux tubes and flux tube recombination

In this work we compute the color fields in the mediator plane between a static quark and a static antiquark using quenched lattice QCD. In special, we see the effect of the quark-antiquark distance on the flux tube. To obtain this results an improved multihit technique is developed and an extend smearing technique is used. Then, we also discuss the flux-tubes in a system composed of two quarks and two antiquarks. The ground and first excited states fields are studied for different dispositions of the system.

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arXiv2012

CuBA - a CUDA implementation of BAMPS

Using CUDA as programming language, we create a code named CuBA which is based on the CPU code "Boltzmann Approach for Many Parton Scattering (BAMPS)" developed in Frankfurt in order to study a system of many colliding particles resulting from heavy ion collisions. Furthermore, we benchmark our code with the Riemann Problem and compare the results with BAMPS. They demonstrate an improvement of the computational runtime, by one order of magitude.

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arXiv2012

Tetraquark and the flux tube recombination

Here we study the static potential for the two quarks and two antiquarks system. First this is done using the tetraquark operator, which has been previously used to calculate the static potential. This is found to give good results in the region where the tetraquark is expected to be the ground state, however failing outside it. To repair this, we resort to a variational method. This let us study the first excited state besides the ground state of the system in two different particle dispositions, one where the quarks are on the same side of a rectangle and the other where they are at opposite sides. Results for the field components and for the lagrangian density are presented.

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arXiv2011

Excited charmonium states from Bethe-Salpeter equation

We solve the Bethe-Salpeter equation for a system of a heavy quark-antiquark pair interacting with a screened linear confining potential. First we show the spinless QFT model is inadequate and fail to describe even gross feature of the quarkonia spectrum. In order to get reliable description the spine degrees of freedom has to be considered. Within the approximation employed we reasonably reproduce known radial excitation of vector charmonium. The BSE favors relatively large string breaking scale $μ\simeq 350MeV$ . Using free charm quark propagators we observe that $J/Ψ$ is the only charmonium left bellow naive quark-antiquark threshold $2m_c$, while the all excited states are situated above this threshold. Within the numerical method we overcome obstacles related with threshold singularity and discuss the consequences of the use of free propagators for calculation of excited states above the threshold.

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arXiv2011

String tension at finite temperature Lattice QCD

The critical curve of string tension as a function of the temperature is computed in SU(3) Lattice QCD. We present the results for the string tension utilizing a pair of Polyakov loop and antiloop, with two different techniques. We compare the colour averaged loop-antiloop which is gauge invariant but is only adequate to study the string tension, and the colour singlet loop-antiloop using the Landau gauge fixing which also enables to compute the coulomb part of the free energy.

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arXiv2011

Colour flux-tubes in static Pentaquark systems

The colour fields created by the static tetraquark and pentaquark systems are computed in quenched SU(3) lattice QCD, with gauge invariant lattice operators, in a 24^3 x 48 lattice at beta=6.2 . We generate our quenched configurations with GPUs, and detail the respective benchmanrks in different SU(N) groups. While at smaller distances the coulomb potential is expected to dominate, at larger distances it is expected that fundamental flux tubes, similar to the flux-tube between a quark and an antiquark, emerge and confine the quarks. In order to minimize the potential the fundamental flux tubes should connect at 120o angles. We compute the square of the colour fields utilizing plaquettes, and locate the static sources with generalized Wilson loops and with APE smearing. The tetraquark system is well described by a double-Y-shaped flux-tube, with two Steiner points, but when quark-antiquark pairs are close enough the two junctions collapse and we have an X-shaped flux-tube, with one Steiner point. The pentaquark system is well described by a three-Y-shaped flux-tube where the three flux the junctions are Steiner points.

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arXiv2011

Study of Tetraquarks with a simple model

Tetraquarks are studied with an approximation which reduces the in- ternal degrees of freedom of the system, using both finite differences and scattering theory. The existence of bound states and resonances is inspected and the masses and widths of the found resonances are calculated.

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arXiv2011

The chiral crossover, static-light and light-light meson spectra, and the deconfinement crossover

We study the chiral crossover, the spectra of light-light and of static-light mesons and the deconfinement crossover at finite temperature T. Our framework is the confining and chiral invariant quark model, related to truncated Coulomb gauge QCD. Since we are dealing with light quarks, where the linear potential dominates the quark condensate and the spectrum, we only specialize in the linear confining potential for the quark-antiquark interaction. We utilize T dependent string tensions previously fitted from lattice QCD data, and a fit of previously computed dynamically generated constituent quark masses. We scan the T effects on the constituent quark mass, on the meson spectra and on the polyakov loop.

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arXiv2011

Finite temperature lattice QCD with GPUs

Graphics Processing Units (GPUs) are being used in many areas of physics, since the performance versus cost is very attractive. The GPUs can be addressed by CUDA which is a NVIDIA's parallel computing architecture. It enables dramatic increases in computing performance by harnessing the power of the GPU. We present a performance comparison between the GPU and CPU with single precision and double precision in generating lattice SU(2) configurations. Analyses with single and multiple GPUs, using CUDA and OPENMP, are also presented. We also present SU(2) results for the renormalized Polyakov loop, colour averaged free energy and the string tension as a function of the temperature.

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arXiv2011

SU(2) Lattice Gauge Theory Simulations on Fermi GPUs

In this work we explore the performance of CUDA in quenched lattice SU(2) simulations. CUDA, NVIDIA Compute Unified Device Architecture, is a hardware and software architecture developed by NVIDIA for computing on the GPU. We present an analysis and performance comparison between the GPU and CPU in single and double precision. Analyses with multiple GPUs and two different architectures (G200 and Fermi architectures) are also presented. In order to obtain a high performance, the code must be optimized for the GPU architecture, i.e., an implementation that exploits the memory hierarchy of the CUDA programming model. We produce codes for the Monte Carlo generation of SU(2) lattice gauge configurations, for the mean plaquette, for the Polyakov Loop at finite T and for the Wilson loop. We also present results for the potential using many configurations ($50\ 000$) without smearing and almost $2\ 000$ configurations with APE smearing. With two Fermi GPUs we have achieved an excellent performance of $200 \times$ the speed over one CPU, in single precision, around 110 Gflops/s. We also find that, using the Fermi architecture, double precision computations for the static quark-antiquark potential are not much slower (less than $2 \times$ slower) than single precision computations.

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arXiv2010

Coulomb Gauge QCD and the Excited Hadron Spectrum

We discuss progress in understanding the light and heavy quark excited hadron spectrum from Coulomb gauge QCD. For light quark systems we highlight the insensitivity to spontaneous chiral symmetry breaking, which predicts Wigner parity-degeneracy in the highly excited hadron spectrum and allows the quark mass momentum dependence to be experimentally probed. For heavy quark meson decays we invoke the Franck-Condon principle, a consequence of small velocity changes for heavy quarks, to extract qualitative, but model independent, structure insight from the momentum distribution of the decay products.

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arXiv2010

Chromoelectric and chromomagnetic fields for the static gluon-quark-antiquark system

The chromoelectric and chromomagnetic fields, created by a static gluon-quark-antiquark system, are computed in the quenched approximation of lattice QCD, in a $24^3\times 48$ lattice at $β=6.2$. We study two geometries, one with a U shape and another with an L shape. The degenerate case of the two gluon glueball is also studied. This is relevant to understand the microscopic structure of hadrons, in particular of hybrids. This also contributes to understand confinement with flux tubes of the chromoelectric field, and to discriminate between the models of fundamental or adjoint tubes.

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arXiv2010

Colour fields in gauge invariant quenched SU(3) Lattice QCD

he colour fields, created by static sources belonging to different SU(3) representations, from the 3 to the 27, are computed in quenched SU(3) lattice QCD, in a 24^3 x 48 lattice at beta=6.2 and a=0.07261(85) fm. We utilize the technique of generalized Wilson Loops to localize the sources, correlated with plaquettes to measure the respective colour fields. We investigate the Casimir scaling of the fields, measured in the static potentials by Bali. We also study the coherence length, comparing with the dual Ginzburg-Landau approach. With the penetration and coherence lengths we determined the Ginzburg-Landau dimensionless parameter, this result is consistent with a type II superconductor picture, and with an effective dual gluon mass of 0.905 +- 0.163 GeV.

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arXiv2010

Colour fields of the static hybrid gluon-quark-antiquark system

The colour fields, created by a static gluon-quark-antiquark system, are computed in quenched SU(3) lattice QCD, in a $24^3\times 48$ lattice at $β=6.2$ and $a=0.07261(85)\,fm$. We study two geometries, one with a U shape and another with an L shape. The particular cases of the two gluon glueball and quark-antiquark are also studied, and the Casimir scaling is investigated in a microscopic perspective. This also contributes to understand confinement with flux tubes and to discriminate between the models of fundamental versus adjoint confining strings, analogous to type-II and type-I superconductivity.

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arXiv2010

Lattice SU(2) on GPU's

We discuss the CUDA approach to the simulation of pure gauge Lattice SU(2). CUDA is a hardware and software architecture developed by NVIDIA for computing on the GPU. We present an analysis and performance comparison between the GPU and CPU with single precision. Analysis with single and multiple GPU's, using CUDA and OPENMP, are also presented. In order to obtain a high performance, the code must be optimized for the GPU architecture, i.e., an implementation that exploits the memory hierarchy of the CUDA programming model. Using GPU texture memory and minimizing the data transfers between CPU and GPU, we achieve a speedup of $200\times$ using 2 NVIDIA 295 GTX cards relative to a serial CPU, which demonstrates that GPU's can serve as an efficient platform for scientific computing. With multi-GPU's we are able, in one day computation, to generate 1 000 000 gauge configurations in a $48^4$ lattice with $β=6.0$ and calculate the mean average plaquette. We present results for the mean average plaquette in several lattice sizes for different $β$. Finally we present results for the mean average Polyakov loop at finite temperature.

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arXiv2010

Tetraquark resonances with the triple flip-flop potential, decays in the cherry in a broken glass approximation

We develop a unitarized formalism to study tetraquarks using the triple flip-flop potential, which includes two meson-meson potentials and the tetraquark four-body potential. This can be related to the Jaffe-Wilczek and to the Karliner-Lipkin tetraquark models, where we also consider the possible open channels, since the four quarks and antiquarks may at any time escape to a pair of mesons. Here we study a simplified two-variable toy model and explore the analogy with a cherry in a glass, but a broken one where the cherry may escape from. It is quite interesting to have our system confined or compact in one variable and infinite in the other variable. In this framework we solve the two-variable Schrödinger equation in configuration space. With the finite difference method, we compute the spectrum, we search for localized states and we attempt to compute phase shifts. We then apply the outgoing spherical wave method to compute in detail the phase shifts and and to determine the decay widths. We explore the model in the equal mass case, and we find narrow resonances. In particular the existence of two commuting angular momenta is responsible for our small decay widths.

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arXiv2010

Confinement and chiral symmetry crossovers

We study the QCD phase diagram, in particular we study the critical points of the two main QCD phase transitions, confinement and chiral symmetry breaking. Confinement drives chiral symmetry breaking, and, due to the finite quark mass, at small density both transitions are a crossover, while they are a first or second order phase transition in large density. We study the QCD phase diagram with a quark potential model including both confinement and chiral symmetry. This formalism, in the Coulomb gauge hamiltonian formalism of QCD, is presently the only one able to microscopically include both a quark-antiquark confining potential and a vacuum condensate of quark-antiquark pairs. This model is able to address all the excited hadrons, and chiral symmetry breaking, at the same token. Our order parameters are the Polyakov loop and the quark mass gap. The confining potential is extracted from the Lattice QCD data of the Bielefeld group. We address how the quark masses affect the critical point location in the phase diagram.

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