N*(1535) electroproduction at high Q2

A covariant spectator quark model is applied to study the gamma N -> N*(1535) reaction in the large Q2 region. Starting from the relation between the nucleon and N*(1535) systems, the N*(1535) valence quark wave function is determined without the addition of any parameters. The model is then used to calculate the gamma N -> N*(1535) transition form factors. A very interesting, useful relation between the A12 and S12 helicity amplitudes for Q2 > GeV^2, is also derived.Comment: Contribution to the proceedings of the 8th International Workshop on the Physics of Excited Nucleons (NSTAR2011), Jefferson Lab, Newport News, VA, USA, May 17-20, 201

Pion structure in a nuclear medium

The structure and electroweak properties of the pion in symmetric nuclear matter are presented in the framework of the Nambu--Jona-Lasinio model. The pion is described as a bound state of a dressed quark-antiquark pair governed by the Bethe-Salpeter equation. For the in-medium current-light-quark properties we use the quark-meson coupling model, which describes successfully the properties of hadron in a nuclear medium. We found that the light-quark condensates, the pion decay constant and pion-quark coupling constant decrease with increasing nuclear matter density. We then predict the modifications of the charge radius of the charged pion in nuclear matter.Comment: 4 pages, 6 figures, accepted version for the QNP2018 proceedings, 8th International Conference on Quarks and Nuclear Physics (QNP2018), November 13-17, 2018, Tsukuba, Ibaraki, Japa

Effects of medium modifications of nucleon form factors on neutrino scattering in dense matter

Effects of the in-medium modifications of nucleon form factors on neutrino interaction in dense matter are presented by considering both the weak and electromagnetic interactions of neutrinos with the constituents of the matter. A relativistic mean field and the quark-meson coupling models are respectively adopted for the effective nucleon mass and in-medium nucleon form factors. We calculate the cross-section of neutrino scattering as well as the neutrino mean free path. We found the cross sections of neutrino scattering in cold nuclear medium decreases when the in-medium modifications of the nucleon weak and electromagnetic form factors are taken into account.This reduction results in the enhancement of the neutrino mean free path, in particular at the baryon density of around a few times of the normal nuclear matter density.Comment: 4 pages, 2 figures, accepted for the QNP2018 proceedings, a talk given at QNP2018, 8th International Conference on Quarks and Nuclear Physics (QNP2018), November 13-17, 2018, Tsukuba, Ibaraki, Japa

Λc+\Lambda^+_c- and Λb\Lambda_b-hypernuclei

$\Lambda^+_c$- and $\Lambda_b$-hypernuclei are studied in the quark-meson coupling (QMC) model. Comparisons are made with the results for $\Lambda$-hypernuclei studied in the same model previously. Although the scalar and vector potentials felt by the $\Lambda$, $\Lambda_c^+$ and $\Lambda_b$ in the corresponding hypernuclei multiplet which has the same baryon numbers are quite similar, the wave functions obtained, e.g., for $1s_{1/2}$ state, are very different. The $\Lambda^+_c$ baryon density distribution in $^{209}_{\Lambda^+_c}$Pb is much more pushed away from the center than that for the $\Lambda$ in $^{209}_\Lambda$Pb due to the Coulomb force. On the contrary, the $\Lambda_b$ baryon density distributions in $\Lambda_b$-hypernuclei are much larger near the origin than those for the $\Lambda$ in the corresponding $\Lambda$-hypernuclei due to its heavy mass. It is also found that level spacing for the $\Lambda_b$ single-particle energies is much smaller than that for the $\Lambda$ and $\Lambda^+_c$.Comment: Latex, 14 pages, 4 figures, text was extended, version to appear in Phys. Rev.

Quark-meson coupling model with the cloudy bag

Using the volume coupling version of the cloudy bag model, the quark-meson coupling model is extended to study the role of pion field and the properties of nuclear matter. The extended model includes the effect of gluon exchange as well as the pion-cloud effect, and provides a good description of the nuclear matter properties. The relationship between the extended model and the EFT approach to nuclear matter is also discussed.Comment: 13 pages, 3 figure