4073106
Multiphase transport model for relativistic heavy ion collisions
We describe in detail how the different components of a multiphase transport (AMPT) model that uses the heavy ion jet interaction generator (HIJING) for generating the initial conditions, Zhang's parton cascade (ZPC) for modeling partonic scatterings, the Lund string fragmentation model or a quark coalescence model for hadronization, and a relativistic transport (ART) model for treating hadronic scatterings are improved and combined to give a coherent description of the dynamics of relativistic heavy ion collisions. We also explain the way parameters in the model are determined and discuss the sensitivity of predicted results to physical input in the model. Comparisons of these results to experimental data, mainly from heavy ion collisions at the BNL Relativistic Heavy Ion Collider, are then made in order to extract information on the properties of the hot dense matter formed in these collisions.
39436824
J/psi absorption by nucleons in the meson-exchange model
We reinvestigate the $J/\ensuremath{\psi}$ dissociation processes induced by the reactions with nucleons, $J/\ensuremath{\psi}+N\ensuremath{\rightarrow}{\overline{D}}^{(*)}+{\ensuremath{\Lambda}}_{c}$, in the meson-exchange model. Main constraints used in this work are vector-meson dominance and charm vector-current conservation. We show that the cross section for $J/\ensuremath{\psi}+N\ensuremath{\rightarrow}\overline{D}+{\ensuremath{\Lambda}}_{c}$ can be larger than that for $J/\ensuremath{\psi}+N\ensuremath{\rightarrow}{\overline{D}}^{*}+{\ensuremath{\Lambda}}_{c}$ when these constraints are imposed. The dependence of the cross sections on the coupling constants is analyzed in detail, and the comparison with the recent quark-interchange model predictions is also made.
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.
119326646
Medium effects on the flow of strange particles in heavy-ion collisions
Strange particles such as the kaon and lambda are useful in probing the properties of dense matter formed in heavy-ion collisions. Here we review the theoretical understanding of their properties in a nuclear medium based on both the effective chiral Lagrangian and the phenomenological hadronic model. We further review the effects due to changes in their in-medium properties on their collective flow in heavy-ion collisions.
118880072
Quark coalescence for charmed mesons in ultrarelativistic heavy-ion collisions
Abstract We investigate effects of charm-quark interactions in a quark–gluon plasma on the production of D and J / ψ mesons in high-energy heavy-ion collisions. Employing a previously constructed coalescence model that successfully reproduces the transverse momentum ( p T ) spectra and elliptic flow ( v 2 ( p T ) ) of light hadrons at RHIC from underlying light-quark distributions at the phase transition temperature  T c , D -meson and J / ψ p T -spectra are evaluated. For the charm-quark distributions, we consider two limiting scenarios: (i) no rescattering, corresponding to perturbative QCD (pQCD) spectra and (ii) complete thermalization including transverse expansion. We find that D -mesons acquire a minimal v 2 inherited from their light-quark content and corresponding semileptonic decay spectra of single electrons practically preserve the v 2 of the parent particles, exhibiting marked differences between the pQCD and thermal scenarios for p T ⩾ 1 GeV . Likewise, the p T -spectra and yields of J / ψ 's differ appreciably in the two scenarios.
16308661
Origin of thermal and non-thermal hard X-ray emission from the Galactic center
We analyse new results of Chandra and Suzaku Observatories which found a flux of hard X-ray emission from the compact region around Sgr A � (r � 100 pc). We suppose that this emission is generated by accretion processes onto the central supermassive blackhole when an unbound part of captured stars obtains an additional momentum. As a result a flux of subrelativistic protons is generated near the galactic center which heats the background plasma up to temperatures about 6–10 keV and produces by inverse bremsstrahlung a flux of non-thermal X-ray emission in the energy range above 10 keV.
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.
119432484
Open clusters 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 proto-clusters have survived. A possible reason is the dispersion of molecular clouds by UV radiation, stellar winds or supernova explosions. We study the cloud dispersion in the embedded clusters by N-body simulations. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
121843826
Hubble constant, lensing, and time delay in Te Ve S
Hubble constant can be determined by the time delay of gravitational lensing systems. As data on time delay observation accumulates, it is time to revisit this approach. As in other dynamical phenomena in scales of galaxy and cluster of galaxies, gravitational lensing in these scales is also plagued by the problem of excess acceleration or gravity (a.k.a. missing mass problem). There are always some accelerations unaccounted for by luminous matter. Usually dark matter is introduced to interpret the discrepancy. However, MOdified Newtonian Dynamics (MOND) is more successful in explaining the excess accelerations in galaxy scale. We adopt TeVeS as the relativistic version of MOND to study gravitational lensing phenomena, and we can evaluate the Hubble constant from the derived time-delay formula. To apply our method, we rely on the CASTLE quasar lensing survey and the Sloan Digital Sky Survey (SDSS). Four samples are suitable for our study. Using only the luminous part of the lensing galaxies, the average of the derived Hubble constant is 68.5 km s^-1Mpc^-1
16205821
Particle propagation in the galactic center and spatial distribution of non-thermal x-rays
We showed that if the non-thermal emission from the galactic center in the range 14–40 keV is due to inverse bremsstrahlung emission of subrelativistic protons, their interactions with hot and cold fractions of the interstellar medium are equally important. Our estimation shows that about 30% of the total non-thermal flux from the GC in the range 14–40 keV is generated in regions of cold gas while the rest is produced by proton interaction with hot plasma. From the spatial distribution of 6.7 keV iron line we concluded the spatial distribution of hot plasma is strongly non-uniform that should be taken into account in analysis of proton propagation in the GC. From the Suzaku data we got independent estimates for the diffusion coefficient of subrelativistic protons in the GC, which was in the range 10 26 –10 27 cm 2 s � 1 .