Ghi Ryang Shin

A relativistic parton cascade with radiation

We consider the evolution of a parton system which is formed at the central rapidity region just after an ultrarelativistic heavy-ion collision. The evolution of the system, which is composed of gluons, quarks and antiquarks, is described by relativistic Boltzmann equations with collision terms including radiation and retardation effects. The equations are solved by the test particle method using Monte Carlo sampling. Our simulations do not show any evidence of kinetic equilibration, unless the cross sections are artificially increased to unrealistically large values.

Studies of parton thermalization at RHIC

We consider the evolution of a parton system which is formed in the central region just after a relativistic heavy ion collision. The parton consists of mostly gluons, minijets, which are produced by elastic scattering between constituent partons of the colliding nuclei. We assume that the system can be described by a semi-classical Boltzmann transport equation, which we solve by means of the test particle Monte Carlo method including retardation. The partons proliferate via secondary radiative gg → ggg processes until the thermalization is reached for some assumptions. The extended system is thermalized at about t = 1.6 fm c−1 with T = 570 MeV and remains in kinetic equilibrium for about 2 fm c−1 with breaking temperature T = 360 MeV in the rapidity central region.

Primitive electrolyte solutions around a charged colloid: density functional approach

ABSTRACT We have developed the density functional theory, which is based both on the modified fundamental-measure theory for the hard spheres and on the weighted-density approximation for the electrostatic residual contribution, for studying the structure of the size-symmetric and asymmetric electrolyte solutions around a charged hard colloid. The calculation shows that the present theory provides an excellent description of the primitive electrolyte solutions and indicates the suitability of the approximations used in the formalism. The preset theory provides better the structural results than the density functional theories based on the excess free energy functional expansion with respect to the bulk ionic density and the hypernetted-chain equation based on the mean spherical approximation over a wide range of colloid sizes, ion concentrations and valence of a colloid. We have confirmed that the present theory is able to predict the phenomena of charge reversal and overcharging occurring near a colloidal interface, in agreement with previous primitive model Monte Carlo simulations and theoretical studies reported in the literature.

Transport theoretical description of collisional energy loss in infinite quark–gluon matter

We study the time evolution of a high-momentum gluon or quark propagating through an infinite, thermalized, partonic medium utilizing a Boltzmann equation approach. We calculate the collisional energy loss of the parton, study its temperature and flavor dependence as well as the momentum broadening incurred through multiple interactions. Our transport calculations agree well with analytic calculations of collisional energy loss where available, but offer the unique opportunity to address the medium response as well in a consistent fashion.

Initial Parton Distribution just after Heavy-Ion Collisions

We study in detail the initial distribution of a parton system that is formed just after relativistic heavy-ion collisions by elastic scattering among the constituent partons and analyze the baryon and strangeness contents of the primary parton system. We present the rapidity and the energy distributions of the system.

Elliptic flow and jet quenching of a parton system after relativistic heavy ion collision

We obtain the initial phase space distribution just after relativistic heavy ion collision by using the Color Glass Condensate (CGC) shattering method incorporating the uncertainty principle and solve the semi-classical Boltzmann equation that includes the gluon radiation processes. We present, as a function of time, the attenuation rate of high pT partons, which have transverse momenta over 6 GeV/c, in the medium that is formed after relativistic heavy ion collision. We calculate the elliptic flow as a function of an impact parameter, the time, and the transverse momentum and present the polar anisotropy, which gives the initial condition for color filamentation.

Note: Density functional theory for uniformly charged hard-sphere ions

The density function theory has been proposed for studying the structural properties of electrolytes containing uniformly charged hard-spherical ions. The calculated result shows good agreement with the corresponding Monte Carlo simulation data of Bohinc et al. [J. Chem. Phys. 145, 234901 (2016)]. The results confirm that the attraction between like-charged planar surfaces is the results of the intra-ionic correlation and depends strongly on the charge distribution of hard-sphere ions.

A study of anisotropic flows at LHC by using purturbative simulation

We study the harmonic flows, for example, the directed, elliptic, third and fourth flows, of the system of partons formed just after relativistic heavy ion collisions. We calculate the minijets produced during the primary collisions by using standard parton distributions for the incoming projectile and the target nucleus. We solve the Boltzmann equations of motion for the system of minijets by using the Monte Carlo method within only the perturbative sector. Based on the calculated flow data, we conclude that the simulation cannot reproduce the experimental results at RHIC and LHC; thus, the nonperturbative sector plays much more important roles even from the earliest stages of heavy ion collisions.

Phase Behaviors of Colloids in Polymer Solutions

A density functional theory (DFT) based on the weighted density has been developed for studying the polymer-induced depletion interaction and phase behaviors of colloids in polymer solutions. The depletion potentials between two colloids induced by the polymer fluids and the colloid-colloid second virial coecients have been calculated. The calculated depletion potentials are compared with the simulation results. The phase diagram shows that short chains can give a more stable dispersion for colloids than long chains. The large colloid/polymer size ratio develops strong attractive interactions. This leads to a broadening of the coexistence region between the solid and the fluid phases of the colloids in a polymer solution.