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Marco Cardoso

Publications and source records attributed to Marco Cardoso.

32 records · Page 2Linked to original sources
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.

hep-lat↗
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.

hep-ph↗
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.

hep-lat↗
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.

hep-lat↗
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.

hep-lat↗
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.

hep-ph↗
arXiv2009

Bottomonium melting at temperature well above Tc

We fit the lattice QCD data of Kaczmarek et al for the free energy F1 and internal energy U1 with a class of Coulomb, constant and linear potentials, both pure and screened, matching the large distance to the short distance parts of the lattice QCD finite temperature energies. We also include the hyperfine potential in F1 and U1. We detail the bottomonium (and charmonium) binding and the melting temperatures, both for the groundstate and for the excited states, relevant for Hard Probes in Heavy Ion Collisions at LHC, where temperatures well above Tc will be reached, much higher than the temperatures reached in previous Heavy Ion Collisions.

hep-ph↗
arXiv2009

Excited baryons as experimental probes of the quark mass

We observe that excited hadrons provide an opportunity to probe from experiment the power-law running of the quark mass in the mid infrared, while the condition m(k)<k remains valid. A relatively clean analysis is possible for the maximum spin excitations of the Delta baryons, analogous to the yrast states in nuclei. Such states are accessible at current experimental facilities such as ELSA and Jlab.

nucl-th↗
arXiv2009

Lattice QCD and Three-Body Exotic Systems in the static limit

The static potentials for quark-antiquark-gluon and 3-gluon systems are computed with lattice QCD methods. For the quark-antiquark-gluon hybrid meson the static potential is obtained for different values of the angle between the quark-gluon and antiquark-gluon segments. The simulations support the formation of an adjoint string for small angles, while for large angles, the adjoint string is replaced by two fundamental strings connecting the gluon and the quarks. For the 3-gluon glueball, we discuss the corresponding Wilson loops and show that the gluons are connected by fundamental strings when the gluons are far apart.

hep-lat↗
arXiv2008

Parity doubling in the high baryon spectrum: near-degenerate three-quark quartets

We report on the first calculation of excited baryons with a chirally symmetric Hamiltonian, modeled after Coulomb gauge QCD (or upgraded from the Cornell meson potential model to a field theory in all of Fock-space) showing the insensitivity to chiral symmetry breaking. As has recently been understood, this leads to doubling between two hadrons of equal spin and opposite parity. As a novelty we show that three-quark, for example Delta states, group into quartets with two states of each parity, all four states having equal angular momentum J. Diagonalizing the chiral charge expressed in terms of quarks we show that the quartet is slightly split into two parity doublets by the tensor force, all splittings decreasing to zero high in the spectrum. Our specific calculation is for the family of maximum-spin excitations of the Delta baryon. We provide a model estimate of the experimental accuracy needed to establish Chiral Symmetry Restoration in the high spectrum. We suggest that a measurement of masses of high-partial wave Delta resonances with an accuracy of 50 MeV should be sufficient to unambiguously establish the approximate degeneracy, and test the concept of running quark mass in the infrared.

hep-ph↗
arXiv2007

Static potential for the quark-antiquark-gluon hybrid system in lattice QCD

The static gluon-quark-antiquark interaction is investigated using lattice QCD techniques. A Wilson loop adequate to the static hybrid three-body system is developed and, using a $24^3 \times 48$ periodic lattice with $β= 6.2$, the potential energy of the system is measured for different geometries. For the medium range behaviour, when the quarks are far apart, we find a string tension which is compatible with two fundamental strings. On the other hand, when the quark and antiquark are nearby, the string tension is larger than two fundamental strings and is compatible with the Casimir scaling.

hep-lat↗
arXiv2006

Confinement of monopole field lines in a superconductor at T=/=0

We apply the Bogoliubov-de Gennes equations to the confinement of a monopole-antimonopole pair in a superconductor. This is related to the problem of a quark-antiquark pair bound by a confining string, consisting of a colour-electric flux tube, dual to the magnetic vortex of type-II superconductors. We study the confinement of the field lines due to the superconducting state and calculate the effective potential between the two monopoles. At short distances the potential is Coulombic and at large distances the potential is linear, as previously determined solving the Ginzburg-Landau equations. The magnetic field lines and the string tension are also studied as a function of the temperature $T$. Because we take into account the explicit fermionic degrees of freedom, this work may open new perspectives to the breaking of chiral symmetry or to colour superconductivity.

hep-ph↗
arXiv2006

Vorticity and magnetic shielding in a type-II superconductor

We study in detail, solving the Bogoliubov-de Gennes equations, the magnetic field, supercurrent and order parameter profiles originated by a solenoid or magnetic whisker inserted in a type-II superconductor. We consider solutions of different vorticities, n, in the various cases. The results confirm the connection between the vorticity, the internal currents and the boundstates in a self-consistent way. The number of boundstates is given by the vorticity of the phase of the gap function as in the case with no external solenoid. In the limiting case of an infinitely thin solenoid, like a Dirac string, the solution is qualitatively different. The quasiparticle spectrum and wave functions are a function of n-n_ext, where n_ext is the vorticity of the solenoid. The flux is in all cases determined by the vorticity of the gap function.

cond-mat.supr-con↗