Chiral Constituent Research Articles

Tensor susceptibility of the QCD vacuum from an effective quark–quark interaction

With an effective quark–quark interaction in the global color symmetry model, the tensor susceptibility of QCD vacuum is calculated. The values we obtained are much smaller than the estimations from QCD sum rules and from chiral constituent quark model.

Nucleon–nucleon interaction in a chiral constituent quark model

This thesis constitute an investigation of finding out whether or not the Goldstone Boson Exchange (GBE) model can give rise to a short-range repulsion in the the nucleon-nucleon (NN) interaction. We used two different approaches based on the Born-Oppenheimer approximation and taking into account Harvey's transformations. Next, we study the NN interaction in a dynamical way using the resonating group method (RGM). We present results for the s-wave phase shifts in the NN scattering. We also introduce some necessary extensions of the GBE model like the contribution of the sigma-meson exchange interaction between quarks or the tensor force and discuss the comparison with the One Gluon Exchange (OGE) results and experiment.

Photoproduction of nucleon resonances and nucleon spin structure function in the resonance region

The photoproduction of nucleon resonances is calculated based on a chiral constituent quark model including both relativistic corrections ${H}_{\mathrm{rel}}$ and two-body exchange currents, and it is shown that these effects play an important role. We also calculate the first moment of the nucleon spin structure function ${g}_{1}{(x,Q}^{2})$ in the resonance region, and obtain a sign-changing point around ${Q}^{2}\ensuremath{\sim}0.27 {\mathrm{GeV}}^{2}$ for the proton.

Effect of higher orbital angular momenta in the baryon spectrum

We have performed a Faddeev calculation of the baryon spectrum for the chiral constituent quark model including higher orbital angular momentum states. We have found that the effect of these states is important, although a description of the baryon spectrum of the same quality as the one given by including only the lowest-order configurations can be obtained. We have studied the effect of the pseudoscalar quark-quark interaction on the relative position of the positive- and negative-parity excitations of the nucleon as well as the effect of varying the strength of the color-magnetic interaction.

Extended van Royen–Weisskopf formalism for lepton–antilepton meson decay widths within nonrelativistic quark models

The classical van Royen–Weisskopf formula for the decay width of a meson into a lepton–antilepton pair is modified in order to include nonzero quark momentum contributions within the meson as well as relativistic effects. Besides, a phenomenological electromagnetic density for quarks is introduced. The meson wave functions are obtained from two different models: a chiral constituent quark model and a quark potential model including instanton effects. The modified van Royen–Weisskopf formula is found to improve systematically the results for the widths, giving an overall good description of all known decays.

Covariant axial form factor of the nucleon in a chiral constituent quark model

The axial form factor G_A of the nucleon is investigated for the Goldstone-boson-exchange constituent quark model using the point-form approach to relativistic quantum mechanics. The results, being covariant, show large contributions from relativistic boost effects. The predictions are obtained directly from the quark-model wave functions, without any further input such as vertex or constituent-quark form factors, and fall remarkably close to the available experimental data.

Nuclear Matter in a Chiral SU(3) Quark Mean-Field Model

A quark meson coupling model based on SU(3)L × SU(3)R symmetry and scale invariance is proposed. The quarks and mesons get masses through symmetry broken. We apply this SU(2) chiral constituent quark model to investigating the nuclear matter at finite temperature and density. The effective baryon masses, compression modulus and hyperon potentials are all reasonable. The critical temperature of liquid-gas phase transition is also calculated in this model.

Quark model study of the η photo-production:

An extensive and systematic study of the recent eta photoproduction data up to 1.2 GeV is presented within a chiral constituent quark model. A model embodying all known nucleonic resonances shows clear need for a yet undiscovered third S11 resonance in the second resonance region, for which we determine the mass (1.729 GeV) and the total width (183 MeV). Furthermore, we extract the configuration mixing angles, an important property of the quark-quark interaction in the quark model, for the resonances S11(1535) and S11(1650), as well as for the resonances D13(1520) and D13(1700). Our results agree well with the quark model predictions. In addition, the partial eta N decay widths and/or the photo-excitation helicity amplitudes for the nucleonic resonances S11(1535), S11(1650), P11(1710), P13(1720), D13(1520), D13(1700), D15(1675), and F15(1680) are also obtained in this approach.

NN scattering phase shifts in a chiral constituent quark model

We study the nucleon–nucleon interaction within a chiral constituent quark model which reproduces successfully the baryon spectra. We calculate the 3S 1 and 1S 0 phase shifts by using the resonating group method. They clearly indicate the presence of a strong repulsive interaction at short distance, due to the spin–flavour symmetry of the quark–quark interaction and of the quark interchange between the two interacting nucleons. A σ-meson exchange quark–quark interaction, providing a medium-range attraction, helps to get closer to the experimental phase shifts.

Extended Goldstone-boson-exchange chiral quark model

The recently discovered pentaquark Θ+ is described within the chiral constituent quark model. Within this picture the flavor-spin interaction between valence quarks inverts the (1s)4 and (1s)3(1p) levels of the four-quark subsystem and consequently the lowest-lying pentaquark is a positive parity, I=0, J=1/2 state of the flavor antidecuplet, similar to the soliton model prediction. Contrary to the soliton model, however, the quark picture predicts its spin-orbit partner with J=3/2. Different interpolating fields intended for lattice calculations of Θ+ are constructed, which have a maximal overlap with this baryon if it is indeed a quark excitation in the 5Q system.

Baryon spectrum in the chiral constituent quark model

The low-lying baryon spectrum predicted by a chiral constituent quark model is examined within an exact Faddeev approach. The reliability of the solutions provided by a truncated hyperspherical harmonic calculation is discussed. We demonstrate that the obtained spectrum is quite reasonable and compatible with the description of the $\mathrm{NN}$ phenomenology in the presence of a standard one-gluon exchange force.

The short-range baryon–baryon interaction in a chiral constituent quark model

The previous analysis of the short-range NN repulsion originating from the Goldstone boson exchange hyperfine interaction between constituent quarks is revisited. We study in which respects the repulsion depends on the radial form of the spin–spin quark–quark force. We show that while the radial form affects the structure of the 6Q wave function, the short-range repulsion in the NN system persists in any case. We extend our analysis to other YN and YY (flavor octet–octet) systems and demonstrate that the flavor–spin hyperfine interaction implies a short-range repulsion in these B=2 systems as well.

Nucleon-nucleon scattering in a chiral constituent quark model

We study the nucleon-nucleon interaction in a chiral constituent quark model by using the resonating group method, convenient for treating the interaction between composite particles. The calculated phase shifts for the 3S1 and 1S0 channels show the presence of a strong repulsive core due to the combined effect of the quark interchange and the spin-flavour structure of the effective quark-quark interaction. Such a symmetry structure stems from the pseudoscalar meson exchange between the quarks and is a consequence of the spontaneous breaking of the chiral symmetry. We perform single and coupled channel calculations and show the role of coupling of the $\Delta\Delta$ and hidden color CC channels on the behaviour of the phase shifts.

Isospin breaking andω→π+π−decay

We study $\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\omega}}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ decay up to and including all orders of the chiral expansion and one-loop level of mesons in a formalism of the chiral constituent quark model. This G-parity forbidden decay is caused by ${m}_{u}\ensuremath{\ne}{m}_{d}$ and the electromagnetic interaction of mesons. We illustrate that in the formalism both the nonresonant contact interaction and $\ensuremath{\rho}$ resonance exchange contribute to this process, and the contribution from $\ensuremath{\rho}$ resonance exchange is dominant. We obtain that the transition matrix element is $〈\ensuremath{\rho}|{H}_{\ensuremath{\rho}\ensuremath{\omega}}|\ensuremath{\omega}〉=[\ensuremath{-}(3956\ifmmode\pm\else\textpm\fi{}280)\ensuremath{-}(1697\ifmmode\pm\else\textpm\fi{}130)i] {\mathrm{MeV}}^{2},$ and the isospin breaking parameter is ${m}_{d}\ensuremath{-}{m}_{u}=3.9\ifmmode\pm\else\textpm\fi{}0.22 \mathrm{MeV}$ at an energy scale of $\ensuremath{\mu}\ensuremath{\sim}{m}_{\ensuremath{\omega}}.$

Nucleon magnetic moments in an extended chiral constituent quark model

We present results for the nucleon magnetic moments in the context of an extended chiral constituent quark model based on the mechanism of the Goldstone boson exchange, as suggested by the spontaneous breaking of chiral symmetry in QCD. The electromagnetic charge-current operator is consistently deduced from the model Hamiltonian, which includes all force components for the pseudoscalar, vector and scalar meson exchanges. Thus, the continuity equation is satisfied for each piece of the interaction, avoiding the introduction of any further parameter. A good agreement with experimental values is found. The role of isoscalar two-body operators, not constrained by the continuity equation, is also investigated.

Possible dibaryons with strangenesss=−5

In the framework of the resonating group method, the binding energy of the six-quark system with strangeness $s=\ensuremath{-}5$ is systematically investigated under the $\mathrm{SU}(3)$ chiral constituent quark model. The single ${\ensuremath{\Xi}}^{*}\ensuremath{\Omega}$ channel calculation with spins $S=0$ and 3 and the coupled $\ensuremath{\Xi}\ensuremath{\Omega}$ and ${\ensuremath{\Xi}}^{*}\ensuremath{\Omega}$ channel calculation with spins $S=1$ and 2 are considered, respectively. The results show the following observations. In the spin=0 case, ${\ensuremath{\Xi}}^{*}\ensuremath{\Omega}$ may be a bound dibaryon with the binding energy being $80.0\ensuremath{\sim}92.4 \mathrm{MeV}.$ In the $S=1$ case, $\ensuremath{\Xi}\ensuremath{\Omega}$ may also be a bound dibaryon. Its binding energy ranges from 26.2 to 32.9 MeV. In the $S=2$ and $S=3$ cases, no evidence of bound dibaryons is found. The scattering lengths in the $S=0$ and $S=1$ cases are also given.

Extension of the GBE chiral constituent quark model

Extension of the GBE chiral constituent quark model

ΞΩ and Ξ*Ω Dibaryons in SU(3) Chiral Quark Model

The binding energy of the six quark system with strangeness s = -5 is investigated by the SU(3) chiral constituent quark model. The single Ξ*Ω channel calculation with spin S = 0 and the coupled ΞΩ - Ξ*Ω channel calculation with spin S = 1 are considered. It is shown that in the spin S = 0 case, the binding energy of Ξ*Ω is ranged from 80.0 to 92.4 MeV, while in the S = 1 case, the additional Ξ*Ω channel increases the binding energy of ΞΩ to a range of 26.2 - 32.9 MeV.

Electromagnetic properties of decuplet hyperons in a chiral quark model with exchange currents

We calculate static electromagnetic properties of the decuplet hyperons in the chiral constituent quark model including electromagnetic exchange currents between quarks. We study the effect of exchange currents on charge and magnetic radii, magnetic and quadrupole moments and radiative decay observables. SUF (3) flavour symmetry breaking due to the mass difference between strange and nonstrange quarks is included. Exchange currents dominate in observables (e.g. quadrupole moments), where one-body currents are suppressed, due to selection rules. The quadrupole moment of the ¯ is mainly sensitive to gluon degrees of freedom; its measurement could be used to determine the strength of the effective gluon exchange interaction between light quarks. We compare our results with the sparse experimental data and with predictions from other models.

A contribution to the study of the enantiomeric composition of a chiral constituent in hazelnut oil used in the detection of adulterated olive oil

A method is proposed for the determination of the adulteration of olive oil with hazelnut oil which is based on the study of the enantiomeric makeup of (E)-5-methylhept-2-en-4-one (filbertone). The possibilities of either using a sample preparation technique or performing direct injection of the samples (i.e., without any kind of sample pretreatment) are considered and both simultaneous distillation extraction followed by gas chromatographic analysis and direct injection in on-line coupled reverse-phase liquid chromatography to gas chromatography are used. In both cases, a chiral stationary phase is employed in the gas chromatography step and the determination of the enantiomeric composition of filbertone is recommended for an accurate evaluation and quick control for detecting the adulteration of olive oil with hazelnut oil.