Schematic model for QCD at finite temperature

The simplest version of a class of toy models for QCD is presented. It is a Lipkin-type model, for the quark-antiquark sector, and, for the gluon sector, gluon pairs with spin zero are treated as elementary bosons. The model restricts to mesons with spin zero and to few baryonic states. The corresponding energy spectrum is discussed. We show that ground state correlations are essential to describe physical properties of the spectrum at low energies. Quantum phase transitions are described in an effective manner, by using coherent states. The appearance of a Goldstone boson for large values of the interaction strength is discussed, as related to a collective state. The formalism is extended to consider finite temperatures. The partition function is calculated, in an approximate way, showing the convenience of the use of coherent states. The energy density, heat capacity, and transitions from the hadronic phase to the quark-gluon plasma are calculated.Departamento de Físic

Modeling pentaquark and heptaquark states

A schematic model for hadronic states, based on constituent quarks and antiquarks and gluon pairs, is discussed. The phenomenological interaction between quarks and gluons is QCD motivated. The obtained hadronic spectrum leads to the identification of nucleon and Δ resonances and to pentaquark and heptaquark states. The predicted lowest pentaquark state (Jπ=1/2⁻) lies at the energy of 1.5 GeV and it is associated to the observed Θ⁺(1540) state. For heptaquarks (Jπ=1/2⁺,3/2⁺) the model predicts the lowest state at 2.5 GeVFacultad de Ciencias Exacta

Schematic model for QCD. III. Hadronic states

The hadronic spectrum obtained in the framework of a QCD-inspired schematic model is presented. The model is the extension of a previous version, whose basic degrees of freedom are constituent quarks, antiquarks, and gluons. The interaction between quarks and gluons is a phenomenological interaction and its parameters are fixed from data. The classification of the states, in terms of quark and antiquark and gluon configurations is based on symmetry considerations, and it is independent of the chosen interaction. Following this procedure, nucleon and Δ resonances are identified, as well as various penta- and hepta-quarks states. The lowest pentaquarks state is predicted at 1.5 GeV and it has negative parity, while the lowest hepta-quarks state has positive parity and its energy is of the order of 2.5 GeV.Facultad de Ciencias Exacta

Modeling pentaquark and heptaquark states

A schematic model for hadronic states, based on constituent quarks and antiquarks and gluon pairs, is discussed. The phenomenological interaction between quarks and gluons is QCD motivated. The obtained hadronic spectrum leads to the identification of nucleon and Δ resonances and to pentaquark and heptaquark states. The predicted lowest pentaquark state (Jπ=1/2⁻) lies at the energy of 1.5 GeV and it is associated to the observed Θ⁺(1540) state. For heptaquarks (Jπ=1/2⁺,3/2⁺) the model predicts the lowest state at 2.5 GeVFacultad de Ciencias Exacta

Schematic model for QCD. III. Hadronic states

The hadronic spectrum obtained in the framework of a QCD-inspired schematic model is presented. The model is the extension of a previous version, whose basic degrees of freedom are constituent quarks, antiquarks, and gluons. The interaction between quarks and gluons is a phenomenological interaction and its parameters are fixed from data. The classification of the states, in terms of quark and antiquark and gluon configurations is based on symmetry considerations, and it is independent of the chosen interaction. Following this procedure, nucleon and Δ resonances are identified, as well as various penta- and hepta-quarks states. The lowest pentaquarks state is predicted at 1.5 GeV and it has negative parity, while the lowest hepta-quarks state has positive parity and its energy is of the order of 2.5 GeV.Facultad de Ciencias Exacta

A schematic model for QCD I: Low energy meson states

A simple model for QCD is presented, which is able to reproduce the meson spectrum at low energy. The model is a Lipkin type model for quarks coupled to gluons. The basic building blocks are pairs of quark-antiquarks coupled to a definite flavor and spin. These pairs are coupled to pairs of gluons with spin zero. The multiplicity problem, which dictates that a given experimental state can be described in various manners, is removed when a particle-mixing interaction is turned on. In this first paper of a series we concentrates on the discussion of meson states at low energy, the so-called zero temperature limit of the theory. The treatment of baryonic states is indicated, also.Comment: 29 pages, 6 figures. submitted to Phys. Rev.

A schematic model for QCD at finite temperature

The simplest version of a class of toy models for QCD is presented. It is a Lipkin-type model, for the quark-antiquark sector, and, for the gluon sector, gluon pairs with spin zero are treated as elementary bosons. The model restricts to mesons with spin zero and to few baryonic states. The corresponding energy spectrum is discussed. We show that ground state correlations are essential to describe physical properties of the spectrum at low energies. Phase transitions are described in an effective manner, by using coherent states. The appearance of a Goldstone boson for large values of the interaction strength is discussed, as related to a collective state. The formalism is extended to consider finite temperatures. The partition function is calculated, in an approximate way, showing the convenience of the use of coherent states. The energy density, heat capacity and transitions from the hadronic phase to the quark-gluon plasma are calculated.Comment: 33 pages, 11 figure

Coherent states and the calculation of nuclear partition functions

Coherent states are introduced as test functions to formulate the statistical mechanics of fermions and bosons interacting via schematic forces. Finite temperature solutions to the Lipkin model and to the Schütte-Da Providencia model are obtained by performing the statistical sum à la Hecht, e.g., by using coherent states. Comparison between present and exacts results is discussed