International Journal of Modern Physics E

The collapsar scenario for long-duration gamma ray bursts (GRBs) has been proposed as a possible astrophysical site for r-process nucleosynthesis. We summarize the status of r-process nucleosynthesis calculations of our group and others in the context of a magnetohydrodynamics + neutrino-heated collapsar model. In the simulations of our group, we begin with a relativistic magnetohydrodynamic model including ray-tracing neutrino transport to describe the development of the black hole accretion disk and the neutrino heating of the funnel region above the black hole. The late-time evolution of the associated jet was then followed using axisymmetric special relativistic hydrodynamics. We utilized representative test particles to follow the temperature, entropy, electron fraction and density for material flowing within the jet from ejection from the accretion disk until several thousand kilometer above the black hole as temperatures fall from 9×10⁹ to 3×10⁸ K. The evolution of nuclear abundances from nucleons to heavy nuclei for ejected test particle trajectories has been solved in a large nuclear reaction network. It was found that an r-process-like abundance distribution forms in material ejected in the collapsar jet.

This work extends the seminal work of Gottfried on the two-body quantum physics of particles interacting through a delta-shell potential to many-body physics by studying a system of nonrelativistic particles when the thermal De-Broglie wavelength of a particle is larger than the range of the potential and the density is such that average distance between particles is larger than the above range. The ability of the delta-shell potential to reproduce some basic properties of the deuteron are examined. Relations for moments of bound-states are derived. The virial expansion is used to calculate the first quantum correction to the ideal gas pressure in the form of the second virial coefficient. Additionally, all thermodynamical functions are calculated up to the first-order quantum corrections. For small departures from equilibrium, the net flows of mass, energy and momentum, characterized by the coefficients of diffusion, thermal conductivity and shear viscosity, respectively, are calculated. Properties of the gas are examined for various values of physical parameters including the case of infinite scattering length when the unitary limit is achieved.

Remarks on strange quarks in the nucleon.

We review how quark models are able to describe the phenomenology of the charm meson sector. The spectroscopy and decays of charmonium and open charm mesons are described in a particular quark model and compared with the data and the results of other existing models in the literature. A quite reasonable global description of the heavy meson spectra is reached. A new assignment of the ψ(4415) resonance as a 3D state leaving aside the 4S state to the X(4360) is tested through the analysis of the resonance structure in e⁺e^- exclusive reactions around the ψ(4415) energy region. We make tentative assignments of some of the XYZ mesons. To elucidate the structure of the 1⁺cs states, i.e., D_s1(2460) and D_s1(2536), we study the strong decay properties of the D_s1(2536) meson. We also perform a calculation of the branching fractions for the semileptonic decays of B and B_s mesons into final states containing orbitally excited charmed and charmed-strange mesons, which have become a very important source of information about the structure of heavy mesons. Analysis of the nonleptonic B-meson decays into D^(*)D_sJ are also included.

The analytical solution of the Schrödinger equation for the Manning–Rosen potential plus a ring-shaped-like potential is obtained by applying the Nikiforov–Uvarov method by using the improved approximation scheme to the centrifugal potential for arbitrary l states. The energy levels are worked out and the corresponding normalized eigenfunctions are obtained in terms of orthogonal polynomials for arbitrary l states.

New data for the quasielastic scattering of ²⁰Ne from a ²⁸Si target at incident energies of 42.5 MeV and 52.3 MeV and for the ²⁸Si(²⁰Ne, ²⁴Mg)²⁴Mg, ²⁸Si(²⁰Ne, ¹⁶O)³²S and ²⁸Si(²⁰Ne, ¹²C)³⁶Ar transfer reactions at 52.3 MeV are reported. Oscillations are observed in the backward angle quasielastic scattering data at 52.3 MeV and the ²⁸Si(²⁰Ne, ¹²C)³⁶Ar transfer cross-sections are of the same magnitude as those for single-α stripping. Coupled reaction channels (CRC) calculations are unable to describe either the quasielastic or the ²⁸Si(²⁰Ne, ¹²C)³⁶Ar transfer data assuming a sequential α transfer process with α-particle form factors from the literature. The addition of direct ⁸Be cluster transfer can provide a reasonable description of both data sets, but only with much larger spectroscopic factors than suggested by simple structure calculations or the large ⁸Be emission thresholds of ²⁰Ne, ²⁸Si and ³⁶Ar, suggesting that the observed structure is of resonance-like origin. An optical model analysis of the quasielastic scattering data is also reported.

The low-lying collective properties of ¹⁰²Pd, ¹⁰⁶Cd, ¹²⁴Te and ¹²⁸Xe nuclei have been established. The relation between gamma-energy over spin E_γ/I as a function of spin I has been drawn to determine the properties of these nuclei in the ground states band. The combined vibrator-γ-soft energy equation was used to calculate the energy of the ground states band for the above nuclei, and it was compared with the calculated energy by using the U(5)–O(6) of the IBM-1. The calculation of the combined equation and the IBM-1 is in good agreement with the measured and other calculated values.

The total cross-sections of the radiative neutron capture processes on ⁹Be, ¹⁴C, ¹⁴N, ¹⁵N and ¹⁶O are described in the framework of the modified potential cluster model with the classification of orbital states according to Young tableaux. The continued interest in the study of these reactions is due, on the one hand, to the important role played by this process in the analysis of many fundamental properties of nuclei and nuclear reactions, and, on the other hand, to the wide use of the capture cross-section data in the various applications of nuclear physics and nuclear astrophysics, and, also, to the importance of the analysis of primordial nucleosynthesis in the Universe. This article is devoted to the description of results for the processes of the radiative neutron capture on certain light atomic nuclei at thermal and astrophysical energies. The considered capture reactions are not part of stellar thermonuclear cycles, but involve in the reaction chains of inhomogeneous Big Bang models.

Using the quasiparticle phonon nuclear model (QPNM) and taking into account the spin–spin interaction, the effects of the spin polarization on spin gyromagnetic factors (g_s) as well as the intrinsic magnetic moments (g_K) of the deformed odd neutron ^155-165Dy isotopes were studied. The calculated values of g_s and g_K are in fair agreement with the experiment as well as with other microscopic calculations. Our calculations indicated that because of the core polarization, the g_s factors of the nucleons in the nucleus reduce noticeably from its free nucleon value and the spin–spin interactions play an important role in the explanation of the quenching of the g_s factors. A very good reproduction of the phenomenological quenching of g_s factor from its free values is obtained for ^155-165Dy.

We study the effect of isospin degree of freedom, incident energy as well as system mass on the behavior of transverse momentum spectra, dN/p_tdp_t, of neutrons and protons. We find that most of the nucleons suffer soft collisions. The effect of isospin degree of freedom on transverse spectra diminishes with the increase in the incident energy. In Fermi energy region, transverse momentum spectra of both protons and neutrons show sensitivity toward the density dependence of symmetry energy.