Floarea Stancu

Stable uudds̄ pentaquarks in the constituent quark model

Abstract The stability of strange pentaquarks uudd s is studied in a constituent quark model based on a flavor–spin hyperfine interaction between quarks. With this interaction model, which schematically represents the Goldstone boson exchange interaction between constituent quarks, the lowest lying strange pentaquark is a p -shell state with positive parity. The flavor–spin interaction lowers the energy of the lowest p -shell state below that of the lowest s -shell state, which has negative parity because of the negative parity of the strange antiquark. It is found that the strange pentaquark can be stable against strong decay provided that the strange antiquark interacts by a fairly strong spin–spin interaction with u and d quarks. This interaction has a form that corresponds to η meson exchange. Its strength may be inferred from the π 0 decay width of D s ∗ mesons.

The tensor part of Skyrme's interaction

Abstract A tensor part is added to central and spin-orbit parts of Skyrmes effective interaction and its contribution to the Hartree-Fock spin-orbit coupling of spherical spin-unsaturated nuclei is analysed. Minor improvements to spin-orbit splittings can be achieved if the strengths of the tensor interaction are treated as free parameters, but the fit to experiment deteriorates if the tensor interaction contribution is estimated for a realistic interaction.

Evolution of nuclear shells with the Skyrme density dependent interaction

We present the evolution of the shell structure of nuclei in Hartree-Fock calculations using Skyrmes density-dependent effective nucleon-nucleon interaction. The role of the tensor part of the Skyrme interaction to the Hartree-Fock spin-orbit splitting in spherical spin unsaturated nuclei is reanalyzed. The contribution of a finite range tensor force to the spin-orbit splitting in closed shell nuclei is calculated. It is found that the exact matrix elements of a Gaussian and of a one-pion exchange tensor potential could be written as a product Skyrmes short range expression times a suppression factor which is almost constant for closed shell nuclei with mass number

The real part of the nucleus-nucleus interaction

A\ensuremath{\geqslant}48

Positive parity pentaquarks in a Goldstone boson exchange model

. The suppression factor is

Nucleon-nucleon interaction in a chiral constituent quark model

\ensuremath{\sim}0.15

X(5568) as a

for the one-pion exchange potential.

su \bar d \bar b

Abstract The real part of the interaction potential for several pairs of magic nuclei has been derived from the Skyrme interaction density functional. The matter density of each nucleus is described by a Fermi distribution adjusted to reproduce the Skyrme-Hartree-Fock densities. Exchange effects due to antisymmetrization are taken into account in an approximate way. The tail of the resulting potential can be accurately approximated with a Woods-Saxon shape beyond the inflexion point of the calculated potential. The parameters of these Woods-Saxon potentials show regularities with respect to the masses of the target and projectile. We have tested the validity of the real part of the potential against elastic scattering data by choosing an imaginary part with the same geometry and a variable strength. For the energy range we consider the calculated grazing angles are somewhat larger than the experimental ones.

tetraquark in a simple quark model

We study the stability of the pentaquarks uuddQbar, uudsQbar and udssQbar (Q = c, b, or t) of positive parity in a constituent quark model based on Goldstone boson exchange interaction between quarks. The pentaquark parity is the antiquark parity times that of a quark excited to a p-shell. We show that the Goldstone boson exchange interaction favors these pentaquarks much more than the negative parity ones of the same flavour content but all quarks in the ground state. We find that the nonstrange pentaquarks are stable against strong decays.

Heavy-flavour pentaquarks in a chiral constituent quark model

We study the short-range nucleon-nucleon interaction in a chiral constituent quark model by diagonalizing a Hamiltonian comprising a linear confinement and a Goldstone boson exchange interaction between quarks. The six-quark harmonic oscillator basis contains up to two excitation quanta. We show that the highly dominant configuration is | s 4 p 2 [42]O[51]FS > due to its specific flavour-spin symmetry. Using the Born-Oppenheimer approximation we find a strong effective repulsion at zero separation between nucleons in both 3 S1 and 1 S0 channels. The symmetry structure of the highly dominant configuration implies the existence of a node in the S-wave relative motion wave function at short distances. The amplitude of the oscillation of the wave function at short range will be however strongly suppressed. We discuss the mechanism leading to the effective short-range repulsion within the chiral constituent quark model as compared to that related with the one-gluon exchange interaction.