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Pedro Bicudo

Publications and source records attributed to Pedro Bicudo.

At least 55 records · Page 3Linked to original sources
arXiv2015

Refined lattice/model investigation of $u d \bar{b} \bar{b}$ tetraquark candidates with heavy spin effects taken into account

We investigate four-quark systems consisting of two heavy anti-bottom quarks and two light up/down quarks. We propose to solve a coupled Schrödinger equation for the anti-bottom-anti-bottom separation using potentials computed via lattice QCD in the limit of static anti-bottom quarks. This coupled Schrödinger equation allows to incorporate effects due to the heavy anti-bottom spins. First exploratory numerical tests are discussed.

hep-ph↗
arXiv2015

Evidence for the existence of $u d \bar{b} \bar{b}$ and the non-existence of $s s \bar{b} \bar{b}$ and $c c \bar{b} \bar{b}$ tetraquarks from lattice QCD

We combine lattice QCD results for the potential of two static antiquarks in the presence of two quarks $q q$ of finite mass and quark model techniques to study possibly existing $q q \bar{b} \bar{b}$ tetraquarks. While there is strong indication for a bound four-quark state for $q q = (ud-du) / \sqrt{2}$, i.e. isospin $I=0$, we find clear evidence against the existence of corresponding tetraquarks with $q q \in \{ uu , (ud+du) / \sqrt{2} , dd \}$, i.e. isospin $I=1$, $q q = s s$ and $q q = c c$.

hep-lat↗
arXiv2014

An unitarized model for tetraquarks with a color flip-flip potential

In this work, a color structure dependent flip-flop potential is developed for the two quarks and two antiquarks system. Then, this potential is applied to a microscopic quark model which, by integrating the internal degrees of freedom, is transformed into a model of mesons with non-local interactions. With this, the T matrix for the system is constructed and meson-meson scattering is studied. Tetraquarks states, interpreted as poles of of the T matrix, both bound states and resonances, are found. Special emphasis is given to the truly exotic $qq\bar{Q}\bar{Q}$ system, but some results for the crypto-exotic $qQ\bar{q}\bar{Q}$ are also presented.

hep-ph↗
arXiv2014

Lattice investigation of heavy meson interactions

We report on a lattice investigation of heavy meson interactions and of tetraquark candidates with two very heavy quarks. These two quarks are treated in the static limit, while the other two are up, down, strange or charm quarks of finite mass. Various isospin, spin and parity quantum numbers are considered.

hep-lat↗
arXiv2014

Matrix model for deconfinement in a SU(Nc) gauge theory in 2+1 dimensions

We use an effective matrix model to study deconfinement in a pure SU(Nc) gauge theory, without quarks, in d=2+1 dimensions. Expanding about a constant background A0 field we construct an effective potential for the eigenvalues of the thermal Wilson line for general Nc and in the large-Nc limit. The numerical results are presented using one, two, and four free parameters, which are determined by fitting directly to the lattice data for the pressure. The matrix model shows a good agreement with numerical lattice simulations for the pressure and the interaction measure, starting from the perturbative limit up to the critical temperature. For the pressure, the details of A0- dependent nonperturbative terms are relevant only in a narrow transition region below ~1.2 Td. This is also the range where the Polyakov loop deviates notably from one. In accordance with the lattice results we find that, up to a trivial factor Nc^2-1, there is only a mild dependence on the number of colors.

hep-ph↗
arXiv2014

Gluon mass at finite temperature in Landau gauge

Using lattice results for the Landau gauge gluon propagator at finite temperature, we investigate its interpretation as a massive type bosonic propagator. In particular, we estimate a gluon mass from Yukawa-like fits to the lattice data and study its temperature dependence.

hep-lat↗
arXiv2014

SU(3) quark-antiquark QCD flux tube

We compute the quark-antiquark flux tube for pure gauge SU(3) in space-time 3 + 1 dimensions. To increase the signal over noise ratio, we apply the improved multihit and extended smearing techniques. We fit the field densities with an appropriate ansatz and we observe both the screening of the color fields and the quantum widening of the flux tube in the mediator plane and in the charge planes.

hep-lat↗
arXiv2014

Many faces of the Landau gauge gluon propagator at zero and finite temperature: positivity violation, spectral density and mass scales

We address several aspects of gluon propagation at zero and finite temperature. In particular, we study the violation of spectral positivity, we discuss a method to extract the Källén-Lehmann spectral density of a particle (be it elementary or bound state) propagator and apply it to compute gluon spectral densities from lattice data. Furthermore, we also consider the interpretation of the Landau gauge gluon propagator at finite temperature as a massive type bosonic propagator.

hep-lat↗
arXiv2013

Lattice QCD signal for a bottom-bottom tetraquark

Utilizing lattice QCD results for the potential of two static antiquarks and two dynamical quarks as well as quark model techniques for the dynamics of two heavy antiquarks in a cloud of two light quarks, we are provided with an accurate framework for the study of possibly existing heavy-heavy-light-light tetraquarks. Among the possible quantum numbers of such a system, we find binding in only one channel, the scalar isosinglet. Solving the Schroedinger equation for the displacement of the heavy antiquarks and taking systematic errors into account, we find an antibottom-antibottom-light-light bound state with a confidence level of around 1.8 sigma ... 3.0 sigma and binding energy of approximately 30 MeV ... 57 MeV.

hep-ph↗
arXiv2013

Matrix model for deconfinement in an SU(2) gauge theory in 2+1 dimensions

We use matrix models to characterize deconfinement at a nonzero temperature T for an SU(2) gauge theory in three spacetime dimensions. At one loop order, the potential for a constant vector potential A0 is ~T^3 times a trilogarithm function of A0/T. In addition, we add various nonperturbative terms to model deconfinement. The parameters of the model are adjusted by fitting the lattice results for the pressure. The nonperturbative terms are dominated by a constant term ~T^2Td, where Td is the temperature for deconfinement. Besides this constant, we add terms which are nontrivial functions of A0/T, both ~T^2Td and ~TTd^2. There is only a mild sensitivity to the details of these nonconstant terms. Overall we find a good agreement with the lattice results. For the pressure, the conformal anomaly, and the Polyakov loop the nonconstant terms are relevant only in a narrow region below ~1.2Td. We also compute the 't Hooft loop, and find that the details of the nonconstant terms enter in a much wider region, up to ~4Td.

hep-ph↗
arXiv2013

Landau gauge fixing on the lattice using GPU's

In this work, we consider the GPU implementation of the steepest descent method with Fourier acceleration for Laudau gauge fixing, using CUDA. The performance of the code in a Tesla C2070 GPU is compared with a parallel CPU implementation.

hep-lat↗
arXiv2012

GPU implementation of a Landau gauge fixing algorithm

We discuss how the steepest descent method with Fourier acceleration for Laudau gauge fixing in lattice SU(3) simulations can be implemented using CUDA. The scaling of the gauge fixing code was investigated using a Tesla C2070 Fermi architecture, and compared with a parallel CPU gauge fixing code.

hep-lat↗
arXiv2012

Generating SU(Nc) pure gauge lattice QCD configurations on GPUs with CUDA

The starting point of any lattice QCD computation is the generation of a Markov chain of gauge field configurations. Due to the large number of lattice links and due to the matrix multiplications, generating SU(Nc) lattice QCD configurations is a highly demanding computational task, requiring advanced computer parallel architectures such as clusters of several Central Processing Units (CPUs) or Graphics Processing Units (GPUs). In this paper we present and explore the performance of CUDA codes for NVIDIA GPUs to generate SU(Nc) lattice QCD pure gauge configurations. Our implementation in one GPU uses CUDA and in multiple GPUs uses OpenMP and CUDA. We present optimized CUDA codes SU(2), SU(3) and SU(4). We also show a generic SU(Nc) code for Nc$\,\geq 4$ and compare it with the optimized version of SU(4). Our codes are publicly available for free use by the lattice QCD community.

hep-lat↗
arXiv2012

Landau Gauge Fixing on GPUs

In this paper we present and explore the performance of Landau gauge fixing in GPUs using CUDA. We consider the steepest descent algorithm with Fourier acceleration, and compare the GPU performance with a parallel CPU implementation. Using $32^4$ lattice volumes, we find that the computational power of a single Tesla C2070 GPU is equivalent to approximately 256 CPU cores.

hep-lat↗
arXiv2012

Study of compact U(1) flux tubes in 3+1 dimensions in lattice gauge theory using GPU's

We utilize Polyakov loop correlations to study (3+1)D compact U(1) flux tubes and the static electron-positron potential in lattice gauge theory. By using field operators it is possible in U(1) lattice gauge theory to probe directly the electric and magnetic fields. In order to improve the signal-to-noise ratio in the confinement phase, we apply the Lüscher-Weiss multilevel algorithm. Our code is written in CUDA, and we run it in NVIDIA FERMI generation GPU's, in order to achieve the necessary performance for our computations.

hep-lat↗
arXiv2012

Landau Gauge Fixing on GPUs and String Tension

We explore the performance of CUDA in performing Landau gauge fixing in Lattice QCD, using the steepest descent method with Fourier acceleration. The code performance was tested in a Tesla C2070, Fermi architecture. We also present a study of the string tension at finite temperature in the confined phase. The string tension is extracted from the color averaged free energy and from the color singlet using Landau gauge fixing.

hep-lat↗
arXiv2012

Colour flux-tubes in static Pentaquark and Tetraquark 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.

hep-lat↗