15375821
Rapidity and system size dependence of anisotropic flows in relativistic heavy ion collisions
We report results from a multiphase transport (AMPT) model on the rapidity and system size dependence of charged hadron anisotropic flows in nuclear collisions at the Relativistic Heavy Ion Collider (RHIC).
20283699
Momentum anisotropies in the quark coalescence model
Based on the quark coalescence model, we derive relations among the momentum anisotropies of mesons and baryons in relativistic heavy ion collisions from a given, but arbitrary azimuthal distribution for the partons. These relations allow us to estimate the higher-order anisotropies in the initial partonic matter from the measured hadronic anisotropies. Besides the familiar even Fourier coefficients such as the elliptic flow, we also pay attention to odd Fourier coefficients such as the directed flow, which has been observed at finite rapidity even at Relativistic Heavy Ion Collider energies.
18778142
Determination of the stiffness of the nuclear symmetry energy from isospin diffusion.
With an isospin- and momentum-dependent transport model, we find that the degree of isospin diffusion in heavy-ion collisions at intermediate energies is affected by both the stiffness of the nuclear symmetry energy and the momentum dependence of the nucleon potential. Using a momentum dependence derived from the Gogny effective interaction, recent experimental data from NSCL-MSU on isospin diffusion are shown to be consistent with a nuclear symmetry energy given by E(sym)(rho) approximately 31.6(rho/rho(0))(1.05) at subnormal densities. This leads to a significantly constrained value of about -550 MeV for the isospin-dependent part of the isobaric incompressibility of isospin asymmetric nuclear matter.
18998652
Pentaquark Baryon Production in Nuclear Reactions *
Using a hadronic model with empirical coupling constants and form factors, we have evaluated the cross sections for the production of exotic pentaquark Θ + and/or Ξ + 5 and Ξ −− 5 in reactions induced by photons, nucleons, pions, and kaons on nucleon targets. We have also predicted the Θ + yield in relativistic heavy ion collisions using a kinetic model that takes into account both Θ + production from the coalescence of quarks and antiquarks in the quark-gluon plasma and the effects due to subsequent hadronic absorption and regeneration.
14560383
Charmonium production from hot hadronic matter
Abstract Charmonium production from D D annihilation in the hadron gas formed in ultra-relativistic heavy-ion collisions is studied. With initial conditions taken from the HIJING parton model, we have estimated the number of J / ψ produced from an expanding hadron gas, using the J / ψ absorption and production cross sections obtained from either an effective Lagrangian or the quark-exchange model. We find that J / ψ production is negligible in heavy-ion collisions at the Relativistic Heavy Ion Collider (RHIC) but may be important at the Large Hadron Collider (LHC), where more charm mesons are produced. Similar results are obtained for ψ ′ production from the hadron gas at RHIC and LHC.
118590053
Recent Progress and New Challenges in Isospin Physics with Heavy-Ion Reactions
The ultimate goal of studying isospin physics via heavy-ion reactions with neutron-rich, stable and/or radioactive nuclei is to explore the isospin dependence of in-medium nuclear effective interactions and the equation of state of neutron-rich nuclear matter, particularly the isospin-dependent term in the equation of state, i.e., the density dependence of the symmetry energy. Because of its great importance for understanding many phenomena in both nuclear physics and astrophysics, the study of the density dependence of the nuclear symmetry energy has been the main focus of the intermediate-energy heavy-ion physics community during the last decade, and significant progress has been achieved both experimentally and theoretically. In particular, a number of phenomena or observables have been identified as sensitive probes to the density dependence of nuclear symmetry energy. Experimental studies have confirmed some of these interesting isospin-dependent effects and allowed us to constrain relatively stringently the symmetry energy at sub-saturation densities. The impact of this constrained density dependence of the symmetry energy on the properties of neutron stars have also been studied, and they were found to be very useful for the astrophysical community. With new opportunities provided by the various radioactive beam facilities being constructed around the world, the study of isospin physics is expected to remain one of the forefront research areas in nuclear physics. In this report, we review the major progress achieved during the last decade in isospin physics with heavy ion reactions and discuss future challenges to the most important issues in this field.
16029130
Line and Continuum Emission from the Galactic Center. III. Origin of 6.4 keV Line Emission from Molecular Clouds in the Galactic Center
We analyze the 6.4 keV line and continuum emission from the molecular cloud Sgr B2 and the source HESS J1745-303, which is supposed to be a complex of molecular gas. From the HESS results it follows that Sgr A is a source of high energy protons, which penetrate into molecular clouds producing there a TeV gamma-ray flux. We present arguments that Sgr A may also produce a flux of subrelativistic protons which generate the 6.4 keV line and bremsstrahlung continuum emission from the clouds.
17280430
Survivability of a star cluster in a dispersing molecular cloud
Star clusters are formed in molecular clouds which are believed to be the birth places of most stars. From recent observational data, Lada & Lada 2003 estimated that only 4% to 7% of the clusters embedded inside molecular clouds have survived. An important mechanism for the disruption of embedded (bound)-clusters is the dispersion of the parent cloud by UV radiation, stellar winds and/or supernova explosions. In this work we study the effect of this mechanism by N-body simulations. We find that most embedded-clusters survive for more than 30 Myr even when different initial conditions of the cluster may introduce some minor variations, but the general result is rather robust.
119468344
Parker-Jeans Instability of Gaseous Disks Including the Effect of Cosmic Rays
We use linear analysis to examine the effect of cosmic rays (CRs) on the Parker-Jeans instability of magnetized self-gravitating gaseous disks. We adopt a slab equilibrium model in which the gravity (including self-gravity) is perpendicular to the midplane and the magnetic field lies along the slab. CRs are described as a fluid, and diffusion is considered only along magnetic field lines. The linearized equations are solved numerically. The system is susceptible to Parker-Jeans instability. In general, the system is less unstable when the CR diffusion coefficient is smaller (i.e., the coupling between the CRs and plasma is stronger). The system is also less unstable if the CR pressure is larger. This is reminiscent of the fact that Jeans instability and Parker instability are less unstable when the gas pressure is larger (or temperature is higher). Moreover, for a large CR diffusion coefficient (or a small CR pressure), perturbations parallel to the magnetic field are more unstable than those perpendicular to it. The other governing factor on the growth rate of the perturbations in different directions is the thickness of the disk or the strength of the external pressure on the disk. In fact, this is the determining factor in some parameter regimes.
118673239
Hubble Constant, Lensing, and Time Delay in Relativistic Modified Newtonian Dynamics
The time delay in galaxy gravitational lensing systems has been used to determine the value of the Hubble constant. As with other dynamical phenomena on the galaxy scale, dark matter is often invoked in gravitational lensing to account for the "missing mass" (the apparent discrepancy between the dynamical mass and the luminous mass). Alternatively, modified gravity can be used to explain the discrepancy. In this paper, we adopt the tensor-vector-scalar gravity (TeVe S), a relativistic version of Modified Newtonian Dynamics, to study gravitational lensing phenomena and derive the formulae needed to evaluate the Hubble constant. We test our method on quasar lensing by elliptical galaxies in the literature. We focus on double-image systems with time delay measurement. Three candidates are suitable for our study: HE 2149–2745, FBQ J0951+2635, and SBS 0909+532. The Hubble constant obtained is consistent with the value used to fit the cosmic microwave background result in a neutrino cosmological model.
118611815
Mass of Galactic Lenses in Modified Newtonian Dynamics
Mu-Chen Chiu, 2 Chung-Ming Ko, 3, 4 Yong Tian, and HongSheng Zhao Institute of Astronomy, National Central University, Jhongli, Taiwan 320, R.O.C. Scottish University Physics Alliance, Institute for Astronomy, the Royal Observatory , University of Edinburgh, Blackford Hill, Edinburgh,EH9 3HJ ,UK Department of Physics, National Central University, Jhongli, Taiwan 320, R.O.C. Center for Complex Systems, National Central University, Jhongli, Taiwan 320, R.O.C. Scottish University Physics Alliance, University of St. Andrews, KY16 9SS,UK (Dated: August 19, 2010)