73573157
Implications of the cosmic infrared background excess for the cosmic star formation
AbstractBy phenomenologically describing the high-redshift star formation history, i.e., $$\dot \rho _ * \left( z \right) \propto \left[ {{{\left( {1 + z} \right)} \mathord{\left/
 {\vphantom {{\left( {1 + z} \right)} {4.5}}} \right.
 \kern-\nulldelimiterspace} {4.5}}} \right]^{ - \alpha }$$, and semi-analytically calculating the fractions of high-redshift Pop I/II and Pop III stars, we investigate the contributions from both high-redshfit Pop I/II and Pop III stars to the observed near-infrared (3 μm < λ < 5 μm) excess in the cosmic infrared background emission. In order to account for the observational level of the near-infrared excess, the power-law index α of the assumed star formation history is constrained to within the range of 0 ≲ α ≲ 1. Such a constraint is obtained under the condition that the viral temperature of dark matter halos belongs to the range of 500 K ⩽ Tvir ⩽ 104 K.
120879129
Effect of a strong magnetic field on the surface electric field of strange stars
We made a detailed study of the properties of the electron layer near the quark surface of strange stars with strong (${\sim}10^{14}{-}10^{17}$ G) magnetic fields. The electrostatic potential and the electric field at the quark surface were calculated as functions of the magnetic field intensity of bare strange stars. Using an ultrastrong ($B\geq 2.5\times10^{16}$ G) magnetic field, we found that the distribution of electrons becomes an exponential function of radial distance, which is quite different in a magnetic field-free case. We also calculated the variation in gap width between the strange core and the normal nuclear crust for strange stars, which is due to magnetic field effect.
119022638
A statistical classification of the unassociated gamma-ray sources in the second Fermi Large Area Telescope Catalog
With the assistance of the identified/associated sources in the second Fermi Large Area Telescope (LAT) catalog, we analyze and resolve the spatial distribution and the distributions of the gamma-ray spectral and variability indices of the remaining 575 unassociated Fermi LAT sources. Consequently, it is suggested that the unassociated sources could statistically consist of Galactic supernova remnants/pulsar wind nebulae, BL Lacertae objects, flat spectrum radio quasars and other types of active galaxies with fractions of 25%, 29%, 41% and 5%, respectively.
121120033
Yields and isomeric ratio of xenon and krypton isotopes from thermal neutron fission of /sup 235/U
The experimental cumulative yields of /sup 85/Kr/sup m/, /sup 87/Kr, /sup 88/Kr, /sup 133/Xe/sup g/, /sup 135/Xe/sup m/, and /sup 135/Xe/sup g/ and the independent isomeric yield of /sup 133/Xe/sup m/ in the thermal neutron fission of /sup 235/U have been measured by the gas chromatographic method. The independent yields of /sup 133/Xe/sup g/, /sup 135/Xe/sup m/, and /sup 135/Xe/sup g/ were deduced with the aid of /sup 133/I and /sup 135/I data. The isomeric yield ratios of /sup 133/Xe and /sup 135/Xe have been computed and compared with theoretical values since they have the same high spin state J = 11/2/sup -/ and low spin ground state J = 3/2/sup +/. The influence of the shell effect on the fission isomeric yield ratio is discussed. From the measured independent yield of Xe isotopes plus the reported data, the Xe-isotopic distribution curve has been constructed. The curve is compared with the isotopic distribution curves of Xe isotopes formed in 11.5 GeV proton interactions with /sup 238/U and Cs isotopes formed in 24 GeV proton interactions with /sup 238/U. Upon fitting the yield curves we find that only those products with N/Z> or =1.48 fit a curve typical of a binarymore » fission process.« less
119705192
Preliminary study of the K N interaction in a chiral constituent quark model
A preliminary investigation of $\overline{K}N$ interaction is performed within a chiral constituent quark model by solving the resonating group method (RGM) equation. The model parameters are taken from our previous work, which gave a satisfactory description of the $S$-, $P$-, $D$-, $F$-wave $\mathit{KN}$ scattering phase shifts. The channel-coupling between $\overline{K}N,\ensuremath{\pi}\ensuremath{\Lambda}$ and $\ensuremath{\pi}\ensuremath{\Sigma}$ is considered, and the scattering phase shifts as well as the bound-state problem of $\overline{K}N$ are dynamically studied. The results show that the $S$-wave $\overline{K}N$ interaction in the isospin $I=0$ channel is attractive, and in the extended chiral SU(3) quark model such an attraction can make for a $\overline{K}N$ bound state, which appears as a $\ensuremath{\pi}\ensuremath{\Sigma}$ resonance in the coupled-channel calculation, while the chiral SU(3) quark model cannot accommodate the existence of a $\overline{K}N$ bound state. It seems that the vector meson exchanges are necessary to be introduced in the quark-quark interactions if one tries to explain the $\ensuremath{\Lambda}(1405)$ as a $\overline{K}N$ bound state or a $\ensuremath{\pi}\ensuremath{\Sigma}$-$\overline{K}N$ resonance state.
52103890
A past capture event at Sagittarius A* inferred from the fluorescent X-ray emission of Sagittarius B clouds
The fluorescent X-ray emission from neutral iron in the molecular clouds [Sagittarius (Sgr) B] indicates that the clouds are being irradiated by an external X-ray source. The source is probably associated with the Galactic central black hole (Sgr A*), which triggered a bright outburst 100 yr ago. We suggest that such an outburst could be due to a partial capture of a star by Sgr A*, during which a jet was generated. Using constraints from the observed flux and the time variability (∼10 yr) of the Sgr B fluorescent emission, we find that the shock produced by the interaction of the jet with the dense interstellar medium represents a plausible candidate for the X-ray source emission.
120385473
Three-dimensional charge dispersion curves from interactions of 11--29 GeV protons with uranium
Experimental nuclear charge dispersion curves from interactions of 11--29 Gev protons with /sup 238/U have been used in the construction of three-dimensional charge dispersion curves. They show the yield variation with mass number A. Neutron-deficient products are distributed over the entire mass range with a peak at A near 87, while the yield of neutron-excessive products is distributed only in the relatively narrow mass region between A=70 and A=150 and has a maximum around A=115. An isobaric yield curve has been obtained by summing up each of the charge dispersion curves and shows a peak, rather than the flat top, in the mass region A=80 to 140 reported previously. The mass yield curves of neutron-excessive and neutron-deficient products are obtained by a decomposition of the charge dispersion curve with two Gaussians, and the mechanism of formation is suggested.
119487137
Coupled-channels study of Lambda K and Sigma K states in the chiral SU(3) quark model
The S-wave $\ensuremath{\Lambda}K$ and $\ensuremath{\Sigma}K$ states with isospin $I=1/2$ are dynamically investigated within the framework of the chiral SU(3) quark model by solving a resonating group method equation. The model parameters are taken from our previous work, which gave a good description of the energies of the baryon ground states, the binding energy of the deuteron, and the experimental data of the nucleon-nucleon (NN) and nucleon-hyperon (NY) scattering. Assumed not to give important contributions in the scattering processes, the s-channel quark-antiquark ($q\overline{q}$) annihilation interactions are not included as a first step. The results show a strong attraction between \ensuremath{\Sigma} and K, which consequently results in a $\ensuremath{\Sigma}K$ quasibound state with about 17-MeV binding energy, unlike the case of $\ensuremath{\Lambda}K$, which is unbound. When the channel coupling of $\ensuremath{\Lambda}K$ and $\ensuremath{\Sigma}K$ is considered, a sharp resonance state near 1670 MeV with spin-parity ${J}^{P}=1/{2}^{\ensuremath{-}}$ is found. The narrow gap of the $\ensuremath{\Lambda}K$ and $\ensuremath{\Sigma}K$ thresholds, the strong attraction between \ensuremath{\Sigma} and K, and the sizable off-diagonal matrix elements of $\ensuremath{\Lambda}K$ and $\ensuremath{\Sigma}K$ are responsible for the appearance of this resonance.
18533521
Deltaron dibaryon structure in chiral SU(3) quark model
We discuss the structure of Deltaron dibaryon in the chiral SU(3) quark model. The energy of Deltaron is obtained by considering the coupling of the $\Delta\Delta$ and $CC$ (hidden color) channels. The effects of various parameters on the Deltaron mass are also studied. It is shown that the mass of Deltaron is lower than the mass of $\Delta\Delta$ but higher than the mass of $\Delta N \pi$.
117386269
N phi states in a chiral quark model
The structures of N{phi} states with spin-parity J{sup p}=3/2{sup -} and J{sup p}=1/2{sup -} are dynamically studied in both the chiral SU(3) quark model and the extended chiral SU(3) quark model by solving a resonating group method (RGM) equation. The model parameters are taken from our previous work, which gave a satisfactory description of the energies of the baryon ground states, the binding energy of the deuteron, the nucleon-nucleon (NN) scattering phase shifts, and the hyperon-nucleon (YN) cross sections. The channel coupling of N{phi} and {lambda}K{sup *} is considered, and the effect of the tensor force which results in the mixing of S and D waves is also investigated. The results show that the N{phi} state has an attractive interaction, and in the extended chiral SU(3) quark model such an attraction plus the channel coupling effect can consequently make for an N{phi} quasi-bound state with several MeV binding energy.
120930803
SPIN-ORBIT FORCE OF HYPERON-NUCLEON INTERACTION IN THE CHIRAL SU(3) QUARK MODEL
The spin-orbit (LS) force of the hyperon-nucleon interaction is studied in the chiral SU(3) quark model. The symmetric LS terms from the one gluon exchange (OGE) and the scalar nonet exchange (OSE) are taken into account. It is shown that two different treatments (the LS coupling from either OGE or OSE being artificially enhanced in order to reproduce the P-3(J) phase shifts of the nucleon-nucleon scattering) lead to very similar LS couplings in the Sigma N(I = 3/2) channel but give quite different results in the Lambda N - Sigma N(I = 1/2) coupled-channel system. A prominent resonance occurs in the P-1(1) state of the Lambda N channel mainly due to the stronger LS(-) couplings in the Lambda N - Sigma N(I = 1/2) coupled-channel system in the OGE enhanced case. Comparatively the Lambda N P-1(1) phase shift curve exhibits a rather smooth behaviour in the OSE enhanced case. Comparing our theoretical results with the experimental data available, and considering the requirement of the baryon spectrum, one can deduce that a stronger color-independent LS coupling is preferred in the chiral quark model. (C) 1998 Elsevier Science B.V.