Instanton-induced Interaction Research Articles

The low-lying hidden- and double-charm tetraquark states in a constituent quark model with instanton-induced interaction

Spectrum of the low-lying hidden- and double-charm tetraquark states are investigated in a nonrelativistic quark potential model, where the instanton-induced interaction is taken as the residual spin-dependent hyperfine interaction between quarks. The model parameters are fixed by fitting the spectrum of the ground hadron states. Our numerical results show that masses of several presently studied tetraquark states are close to those of the experimentally observed candidates of exotic meson, which indicates that the corresponding compact tetraquark components may take considerable probabilities in those observed exotic states.

Study of the Ground-State Energies of Some Nuclei Using Hybrid Model

The quark-quark (QQ) interaction as a perturbed term to the nucleon-nucleon interaction (NN) without any coupling between them is studied in a hybrid model. This model is used to calculate the ground-state energies of 2H1 and 4He2 nuclei. In a semirelativistic framework, this model is encouraged for light nuclei and the instanton-induced interaction by using the QQ potential and the NN interaction for a small scale around the hadron boundaries. This hybrid model depends on two theories, the one-boson exchange potential (OBEP) and the Cornell-dressed potential (CDP) for QQ. A small effect of quark-quark interaction is obtained on the values of the ground-state energies, around 6.7 and 1.2 percentage for 2H1 and 4He2, respectively nuclei.

Effect of confined one-gluon-exchange potential and instanton-induced interaction on nucleon–nucleon interaction

The effect of confined one-gluon-exchange potential and instanton-induced interaction potential in the singlet (1S0) and triplet (3S1) channels for nucleon–nucleon interaction has been investigated in the framework of the relativistic harmonic model using the resonating group method in the adiabatic limit with the Born–Oppenheimer approximation. The contributions of the different components of the interaction potentials have been analyzed.

Flavor-singlet hidden charm pentaquark

A new type of charm pentaquark $P_{cs}$ with quark content $c\bar{c}uds$ in light-flavor singlet state is studied in the quark model. This state is analogous to the $P_{c}$ with $c\bar{c}uud$ in light-flavor octet, which was observed in LHC in 2015. Considering various combinations of color, spin and light flavor as internal quantum numbers in $P_{cs}$, we investigate the mass ordering of the $P_{cs}$'s by adopting both the one-gluon exchange interaction and the instanton-induced interaction in the quark model. The most stable configuration of $P_{cs}$ is identified to be total spin $1/2$ in which the $c\bar{c}$ is combined to be color octet and spin $1$, while the $uds$ cluster is in a color octet state. The other color octet configurations, the total spin $1/2$ state with the $c\bar{c}$ spin 0 and the state with total spin $3/2$ and $c\bar{c}$ spin 1, are found as excited states. We also discuss possible decay modes of these charm pentaquarks.

Nucleon-nucleon interaction with one-pion exchange and instanton-induced interactions

Singlet $(^{1}S_{0})$ and triplet $(^{3}S_{1})$ nucleon-nucleon potentials are obtained in the framework of the SU(2) nonrelativistic quark model using the resonating-group method in the Born-Oppenheimer approximation. The full Hamiltonian used in the investigation includes the kinetic energy, two-body confinement potential, one-gluon-exchange potential (OGEP), one-pion exchange potential (OPEP), and instanton induced interaction (III), which includes the effect of quark exchange between the nucleons. The contribution of the OGEP, III, and OPEP to the nucleon-nucleon adiabatic potential is discussed.

Investigations on the I(JP) = 0(3+) hidden color hexaquark states

Here we investigate the energies of hidden color hexaquark states with quantum numbers \(I(J^{p})=0(3^{+})\) within the framework of the constituent quark model. The hyperfine interaction between quarks is taken to be the instanton-induced interaction, and mixing between different hexaquark configurations caused by hyperfine interaction between quarks is considered. Numerical results show that energies of several obtained hexaquark states are very close to the mass of the experimentally observed \( d^{\ast}\) resonance, it indicates that these states may be the dominant components of \( d^{\ast}\) baryon resonance, if \( d^{\ast}\) is a genuine hexaquark dominated baryon state.

Mixing of the low-lying three- and five-quarkΩstates with negative parity

Mixing of the low-1/2^{-}$ and $3/2^{-}$ is investigated, employing an instanton-induced quark-antiquark pair creation model, which precludes transitions between $s^{3}$ and $s^{4}\bar{s}$ configurations. Models with hyperfine interactions between quarks of three different kinds, namely, one-gluon-exchange, Goldstone-boson-exchange (GBE) and an instanton-induced interaction (INS) are called OGE, GBE and INS models, respectively. Numerical results show that the instanton-induced pair creation causes strong mixing between the three- and five-quark configurations with spin 3/2, and that this mixing decreases the energy of the lowest spin 3/2 states in all three different hyperfine interaction models to $\sim 1750\pm50$ MeV. On the other hand, transition couplings between $s^3$ and $s^{3}q\bar{q}$ states with spin 1/2 caused by instanton-induced $q\bar{q}$ creation is very small and the resulting mixing of three- and five-quark configurations in the OGE and INS models is negligible, while the mixing of the spin 1/2 states in GBE model is not, but effects of this mixing on energies of mixed states are also very small. Accordingly, the lowest $\Omega$ states with negative parity in all three hyperfine interactions models have spin 3/2.

Study of $$qqqc\bar c$$ five quark system with three kinds of quark-quark hyperfine interaction

The low-lying energy spectra of five quark systems $uudc\bar{c}$ (I=1/2, S=0) and $udsc\bar{c}$ (I=0, S=-1) are investigated with three kinds of schematic interactions: the chromomagnetic interaction, the flavor-spin dependent interaction and the instanton-induced interaction. In all the three models, the lowest five quark state ($uudc\bar{c}$ or $udsc\bar{c}$) has an orbital angular momentum L=0 and the spin-parity $J^{P}=1/2^{-}$; the mass of the lowest $udsc\bar{c}$ state is heavier than the lowest $uudc\bar{c}$ state.

Implementation of the Nambu Jona-Lasinio model in hybrid stars

The model of Nambu and Jona-Lasinio has been extensively used to model the possible occurrence of quark matter in the core of compact stars. While based entirely on similar physical assumptions, previous studies have been performed using a variety of model versions, differing in both the number of active quark flavors and the structure of the quark-quark interaction. We discuss the results of our systematic analysis, designed to clarify the role of the vector and instanton-induced interactions in determining the properties of hybrid stars. The results of our calculations, carried out using a state-of-the-art description of the hadronic phase, show that the instanton-induced interaction does not affect the stiffness of the quark matter equation of state, whereas the effect of the repulsive vector interaction is sizable. However, no values of the corresponding coupling constants allow for the formation of a stable core of quark matter.

Ground State Meson Spectrum in a Relativistic Model with Instanton Induced Interaction

The mass spectrum of the S-wave mesons is considered in the frame work of relativistic harmonic model (RHM). The full Hamiltonian used in the investigation has the Lorentz scalar plus a vector harmonic-oscillator potential, the confined-one-gluon-exchange potential (COGEP) and the instanton-induced quark-antiquark interaction (III). A good description of the mass spectrum is obtained. The respective role of III and COGEP in the S-wave meson spectrum is discussed.

The effect of instanton-induced interaction on P-wave meson spectra in constituent quark model

The mass spectrum of the P-wave mesons is considered in a non-relativistic constituent quark model. The full Hamiltonian used in the investigation includes the kinetic energy, the confinement potential, the one-gluon-exchange potential (OGEP) and the instanton-induced quark-antiquark interaction (III). A good description of the mass spectrum is obtained. The respective role of III and OGEP in the P-wave meson spectrum is discussed.

P-wave pentaquark and its decay in the quark model with instanton induced interaction

$P$-wave pentaquarks with strangeness $+1$, $I=0$, and ${J}^{P}=1/{2}^{+}$ are studied in the nonrelativistic quark model with instanton induced interaction (III). We present their mass splittings and orbital-spin-isospin-color structures. It is found that decompositions of the wave functions are sensitive to III, while the mass splittings are insensitive. The decay of the lowest energy pentaquark, ${\ensuremath{\Theta}}^{+}$, is found to be suppressed when the contribution of III is increased. Spin structure of the dominant components of the wave function is studied.

Thermodynamics of Two-Flavor Quark Matter in the Instanton Vacuum at Finite Chemical Potential

The thermodynamics of quark matter consisting of two light flavors (up and down) in the instanton vacuum is investigated at finite chemical potential (μ) and partly at finite temperature. The derivation of the instanton-induced interaction is performed by a method based on the LSZ reduction formula, which is a new procedure for the case of finite μ. The finite μ form factors arising from zero mode quarks are calculated without approximation. Phase structures for N c = 3 and N c =: 2 are investigated using the thermodynamic potential in the mean-field approximation. It is found that in most cases the double-condensate phase, in which both chiral and diquark condensates coexist, can be realized between the pure chiral condedsate and pure diquark condensate phases. In addition, several thermodynamic quantities, including occupation numbers, quark number densities and the latent heat in the chiral phase transition, are also computed numerically.

Meson spectrum in a non-relativistic model with instanton-induced interaction

On the basis of the phenomenological non-relativistic quark model, we have obtained the ground-state masses of the light pseudo-scalar and vector mesons. The full Hamiltonian used in the investigation includes the kinetic energy, the confinement potential, the one-gluon-exchange potential and the instanton-induced quark–antiquark interaction. A good agreement is obtained with the experimental masses. The η–η′ splitting is explained. The limitation of the perturbative treatment for estimating the π–ρ splitting using OGEP is also pointed out.

Ds*+(2317) and Ds*+(2460): Tetraquarks bound by the 't Hooft instanton-induced interaction?

We calculate the influence of the 't Hooft interaction on the single-charm ($\mathrm{C}=1$) tetraquark ($cq{\overline{q}}^{2}$) mass spectrum and find that three SU(3)-flavor multiplets (${\overline{\mathbf{3}}}_{\mathbf{A}},\mathbf{6},\overline{\mathbf{15}}$) are significantly lowered, while the ${\overline{\mathbf{3}}}_{\mathbf{S}}$-plet is lifted, as compared with their unperturbed masses. States with the ${D}_{s}^{+}$ quantum numbers appear in two of the three lowered multiplets. The lower of the two states drops below both of the Okubo-Zweig-Iizuka (OZI)-allowed decay thresholds, thus being identified with ${D}_{s}^{*+}(2320)$, while the heavier state drops below the $\ensuremath{\eta}+{D}_{s}^{+}$ threshold, but stays above the $K+D$ one. A signature prediction of this theory is the lowering of the exotic tetraquark $\mathbf{6}$-plet and $\overline{\mathbf{15}}$-plet: most of these states cannot consist of only one quark and one antiquark. As a test we suggest a search for two quasistable exotic tetraquarks with open-charm and strangeness: the (isotriplet) $cs\overline{q}\overline{q}$ and the (isodoublet) $cq\overline{s}\overline{s}$.

Meson spectrum in a relativistic harmonic model with instanton-induced interaction

On the basis of the phenomenological relativistic harmonic model for quarks, we have obtained the ground-state masses of the light pseudo-scalar and vector mesons. The full Hamiltonian used in the investigation has Lorentz scalar + vector confinement potential, along with one-gluon-exchange potential (OGEP) and the instanton-induced quark-antiquark interaction. A good agreement is obtained with the experimental masses. The respective role of instanton-induced interaction and OGEP for the determination of the meson masses is discussed.

Electromagnetic properties of baryons in a relativistic quark model

Results on electromagnetic form factors of the nucleon and photon transition form factors of non-strange baryon resonances calculated in a relativistically covariant quark model based on the Bethe-Salpeter equation are presented. The relevance of the instanton-induced quark interaction on these properties is discussed.

Electroweak form factors of non-strange baryons

We compute electroweak form factors of the nucleon and photon transition form factors of non-strange baryon resonances up to the third resonance region in a model with instanton-induced interaction. The calculation is based on the Bethe-Salpeter equation for three light constituent quarks and is fully relativistic (U. Löring et al., Eur. Phys. J. A 10, 309 (2001)). Static nucleon properties and photon resonance couplings are in good agreement with experiment and the Q2 behaviour of the experimentally known form factors up to large momentum transfer is accounted for.

Instantons and the DeltaI = 1/2 rule.

The instanton-induced interaction leads to a significant enhancement of the Ao weak amplitude determining the DeltaI = 1/2 rule, through the contribution of operators with dimension d = 9, as we show in the weak K--> pi(pi) decay.

A relativistic quark model for mesons with an instanton-induced interaction

We present new results of a relativistic quark model based on the Bethe-Salpeter equation in its instantaneous approximation. Assuming a linearly rising confinement potential with an appropriate spinorial structure in Dirac space and adopting a residual interaction based on instanton effects, we can compute masses of the light mesons up to highest observed angular momenta with a natural solution of the $U_A(1)$ problem. The calculated ground states masses and the radial excitations describe the experimental results well. In this paper, we will also discuss our results concerning numerous meson decay properties. For processes like $\pi^+/K^+\to e^+\nu_e\gamma$ and $0^-\to\gamma\gamma$ at various photon virtualities, we find a good agreement with experimental data. We will also comment on the form factors of the $K_{\ell 3}$ decay and on the decay constants of the $\pi$, $K$ and $\eta$ mesons. For the sake of completeness, we will furthermore present the electromagnetic form factors of the charged $\pi$ and $K$ mesons as well as a comparison of the radiative meson decay widths with the most recent experimental data.