N K Pi molecular state with I=1 and J(Pi)=3/2-

The structure of the molecule-like state of $NK\pi$ with spin-parity $J^{\pi}={3/2}^-$ and isospin I=1 is studied within the chiral SU(3) quark model. First we calculate the $NK$, $N\pi$, and $K\pi$ phase shifts in the framework of the resonating group method (RGM), and a qualitative agreement with the experimental data is obtained. Then we perform a rough estimation for the energy of $(NK\pi)_{J^{\pi}={3/2}^-,I=1}$, and the effect of the mixing to the configuration $(\Delta K)_{J^{\pi}={3/2}^-,I=1}$ is also considered. The calculated energy is very close to the threshold of the $NK\pi$ system. A detailed investigation is worth doing in the further study.Comment: 11 pages, 3 figures; accepted for publication in Phys. Rev.

N K and Delta K states in the chiral SU(3) quark model

The isospin I=0 and I=1 kaon-nucleon $S$, $P$, $D$, $F$ wave phase shifts are studied in the chiral SU(3) quark model by solving the resonating group method (RGM) equation. The calculated phase shifts for different partial waves are in agreement with the experimental data. Furthermore, the structures of the $\Delta K$ states with L=0, I=1 and I=2 are investigated. We find that the interaction between $\Delta$ and $K$ in the case of L=0, I=1 is attractive, which is not like the situation of the $NK$ system, where the $S$-wave interactions between $N$ and $K$ for both I=0 and I=1 are repulsive. Our numerical results also show that when the model parameters are taken to be the same as in our previous $NN$ and $YN$ scattering calculations, the $\Delta K$ state with L=0 and I=1 is a weakly bound state with about 2 MeV binding energy, while the one with I=2 is unbound in the present one-channel calculation.Comment: 14 pages, 6 figures. PRC70,064004(2004

Sigma_c Dbar and Lambda_c Dbar states in a chiral quark model

The S-wave Sigma_c Dbar and Lambda_c Dbar states with isospin I=1/2 and spin S=1/2 are dynamically investigated within the framework of a chiral constituent quark model by solving a resonating group method (RGM) equation. The results show that the interaction between Sigma_c and Dbar is attractive, which consequently results in a Sigma_c Dbar bound state with the binding energy of about 5-42 MeV, unlike the case of Lambda_c Dbar state, which has a repulsive interaction and thus is unbound. The channel coupling effect of Sigma_c Dbar and Lambda_c Dbar is found to be negligible due to the fact that the gap between the Sigma_c Dbar and Lambda_c Dbar thresholds is relatively large and the Sigma_c Dbar and Lambda_c Dbar transition interaction is weak.Comment: 7 pages,2 figures. arXiv admin note: text overlap with arXiv:nucl-th/0606056 by other author

Baryon-meson interactions in chiral quark model

Using the resonating group method (RGM), we dynamically study the baryon-meson interactions in chiral quark model. Some interesting results are obtained: (1) The Sigma K state has an attractive interaction, which consequently results in a Sigma K quasibound state. When the channel coupling of Sigma K and Lambda K is considered, a sharp resonance appears between the thresholds of these two channels. (2) The interaction of Delta K state with isospin I=1 is attractive, which can make for a Delta K quasibound state. (3) When the coupling to the Lambda K* channel is considered, the N phi is found to be a quasibound state in the extended chiral SU(3) quark model with several MeV binding energy. (4) The calculated S-, P-, D-, and F-wave KN phase shifts achieve a considerable improvement in not only the signs but also the magnitudes in comparison with other's previous quark model study.Comment: 5 pages, 2 figures. Talk given at 3rd Asia Pacific Conference on Few-Body Problems in Physics (APFB05), Korat, Nakhon Ratchasima, Thailand, 26-30 Jul 200

Resonating group method study of kaon-nucleon elastic scattering in the chiral SU(3) quark model

The chiral SU(3) quark model is extended to include an antiquark in order to study the kaon-nucleon system. The model input parameters $b_u$, $m_u$, $m_s$ are taken to be the same as in our previous work which focused on the nucleon-nucleon and nucleon-hyperon interactions. The mass of the scalar meson $\sigma$ is chosen to be 675 MeV and the mixing of $\sigma_0$ and $\sigma_8$ is considered. Using this model the kaon-nucleon $S$ and $P$ partial waves phase shifts of isospin I=0 and I=1 have been studied by solving a resonating group method (RGM) equation. The numerical results of $S_{01}$, $S_{11}$, $P_{01}$, $P_{03}$, and $P_{11}$ partial waves are in good agreement with the experimental data while the phase shifts of $P_{13}$ partial wave are a little bit too repulsive when the laboratory momentum of the kaon meson is greater than 500 MeV in this present calculation.Comment: 17 pages, 6 figures. Final version for publicatio

A Generic Dynamical Model of Gamma-ray Burst Remnants

The conventional generic model is deemed to explain the dynamics of $\gamma$-ray burst remnants very well, no matter whether they are adiabatic or highly radiative. However, we find that for adiabatic expansion, the model could not reproduce the Sedov solution in the non-relativistic phase, thus the model needs to be revised. In the present paper, a new differential equation is derived. The generic model based on this equation has been shown to be correct for both radiative and adiabatic fireballs, and in both ultra-relativistic and non-relativistic phase.Comment: 10 pages, LaTeX, 4 postscript figures, accepted for publication in MNRA

S, P, D, F wave KN phase shifts in the chiral SU(3) quark model

The $S$, $P$, $D$, $F$ wave $KN$ phase shifts have been studied in the chiral SU(3) quark model by solving a resonating group method equation. The numerical results of different partial waves are in agreement with the experimental data except for the cases of $P_{13}$ and $D_{15}$, which are less well described when the laboratory momentum of the kaon meson is greater than 400 MeV.Comment: Prepared for 10th International Symposium on Meson-Nucleon Physics and the Structure of the Nucleon (MENU 2004), Beijing, China, 29 Aug - 4 Sep 200

Optical Flashes and Very Early Afterglows in Wind Environments

The interaction of a relativistic fireball with its ambient medium is described through two shocks: a reverse shock that propagates into the fireball, and a forward shock that propagates into the medium. The observed optical flash of GRB 990123 has been considered to be the emission from such a reverse shock. The observational properties of afterglows suggest that the progenitors of some GRBs may be massive stars and their surrounding media may be stellar winds. We here study very early afterglows from the reverse and forward shocks in winds. An optical flash mainly arises from the relativistic reverse shock while a radio flare is produced by the forward shock. The peak flux densities of optical flashes are larger than 1 Jy for typical parameters, if we do not take into account some appropriate dust obscuration along the line of sight. The radio flare always has a long lasting constant flux, which will not be covered up by interstellar scintillation. The non-detections of optical flashes brighter than about 9th magnitude may constrain the GRBs isotropic energies to be no more than a few $10^{52}$ ergs and wind intensities to be relatively weak.Comment: 21 pages, 6 figures, accepted by MNRAS on March 7, 200