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Wei-Liang Qian

Publications and source records attributed to Wei-Liang Qian.

At least 127 records · Page 7Linked to original sources
arXiv2016

(Anti-) de Sitter Electrically Charged Black Hole Solutions in Higher-Derivative Gravity

In this paper, static electrically charged black hole solutions with cosmological constant are investigated in an Einstein-Hilbert theory of gravity with additional quadratic curvature terms. Beside the analytic Schwarzschild (Anti-) de Sitter solutions, non-Schwarzschild (Anti-) de Sitter solutions are also obtained numerically by employing the shooting method. The results show that there exist two groups of asymptotically (Anti-) de Sitter spacetimes for both charged and uncharged black holes. In particular, it was found that for uncharged black holes the first group can be reduced to the Schwarzschild (Anti-) de Sitter solution, while the second group is intrinsically different from a Schwarzschild (Anti-) de Sitter solution even when the charge and the cosmological constant become zero.

gr-qc↗
arXiv2016

Effect of stochastic transition in the fundamental diagram of traffic flow

In this work, we propose an alternative stochastic model for the fundamental diagram of traffic flow with minimal number of parameters. Our approach is based on a mesoscopic viewpoint of the traffic system in terms of the dynamics of vehicle speed transitions. A key feature of the present approach lies in its stochastic nature which makes it possible to study not only the flow-concentration relation, namely, the fundamental diagram, but also its uncertainty, namely, the variance of the fundamental diagram \textemdash an important characteristic in the observed traffic flow data. It is shown that in the simplified versions of the model consisting of only a few speed states, analytic solutions for both quantities can be obtained, which facilitate the discussion of the corresponding physical content. We also show that the effect of vehicle size can be included into the model by introducing the maximal congestion density $k_{max}$. By making use of this parameter, the free flow region and congested flow region are naturally divided, and the transition is characterized by the capacity drop at the maximum of the flow-concentration relation. The model parameters are then adjusted to the observed traffic flow on the I-80 Freeway Dataset in the San Francisco area from the NGSIM program, where both the fundamental diagram and its variance are reasonably reproduced. Despite its simplicity, we argue that the current model provides an alternative description for the fundamental diagram and its uncertainty in the study of traffic flow.

physics.soc-ph↗
arXiv2013

Decomposition of fluctuating initial conditions and flow harmonics

Collective flow observed in heavy ion collisions is largely attributed to initial geometrical fluctuations, and it is the hydrodynamic evolution of the system that transforms those initial spatial irregularities into final state momentum anisotropies. Cumulant analysis provides a mathematical tool to decompose those initial fluctuations in terms of radial and azimuthal components. It is usually thought that a specified order of azimuthal cumulant, for the most part, linearly produces flow harmonic of the same order. In this work, we carry out a systematic study on the connection between cumulants and flow harmonics using a hydrodynamic code called NeXSPheRIO. We conduct three types of calculations, by explicitly decomposing the initial conditions into components corresponding to a given eccentricity and studying the out-coming flow through hydrodynamic evolution. It is found that for initial conditions deviating significantly from Gaussian, such as those from NeXuS, the linearity between eccentricities and flow harmonics partially breaks down. Combining with the effect of coupling between cumulants of different orders, it causes the production of extra flow harmonics of higher orders. We argue that these results can be seen as a natural consequence of the non-linear nature of hydrodynamics, and they can be understood intuitively in terms of the peripheral-tube model.

hep-ph↗
arXiv2012

Further results on peripheral-tube model for ridge correlation

Peripheral one-tube model has shown to be a nice tool for dynamically understanding several aspects of ridge structures in long-range two-particle correlations, observed experimentally and obtained also in our model calculations using NexSPheRIO code. Here, we study an extension of the model, to initial configurations with several peripheral tubes distributed randomly in azimuth. We show that the two-particle correlation is almost independent of the number of tubes, although the flow distribution becomes indeed strongly event dependent. In our picture, the ridge structures are causally connected not only in the longitudinal direction but also in azimuth.

hep-ph↗
arXiv2012

On the origin of trigger-angle dependence of di-hadron correlations

The STAR Collaboration reported measurements of di-hadron azimuthal correlation in medium-central Au+Au collisions at 200 A$\,$GeV, where the data are presented as a function of the trigger particle's azimuthal angle relative to the event plane $ϕ_s $. In particular, it is observed that the away-side correlation evolves from single- to double-peak structure with increasing $ϕ_s$. In this work, we present the calculated correlations as functions of both $ϕ_s$ and particle transverse momentum $p_T $, using the hydrodynamic code NeXSPheRIO. The results are found to be in reasonable agreement with the STAR data. We further argue that the above $ϕ_s$ dependence of the correlation structure can be understood in terms of one-tube model, as due to an interplay between the background elliptic flow caused by the initial state global geometry and the flow produced by fluctuations.

hep-ph↗
arXiv2012

Hypernclear in the improved quark mass density- dependent model

The improved quark mass density- dependent model, which has been successfully used to describe the properties of both finite nuclei and bulk nuclear matter, is extended to include the strange quark. The parameters of the model are determined by the saturation properties of bulk matter. Then the given parameter set is employed to investigate both the properties of strange hadronic matter and those of $Λ$ hypernuclei. Bulk strange hadronic matter consisting of nucleons, $Λ$- hyperons and $Ξ$- hyperons is studied under mean-field approximation. Among others, density dependence of the effective baryon mass, saturation properties and stability of the physical system are discussed. For single-$Λ$ hypernuclei, single particle energies of $Λ$ hyperon is evaluated. In particular, it is found that the present model produces a small spin-orbit interaction, which is in agreement with the experimental observations. The above results show that the present model can consistently describe the properties of strange hadronic matter, as well as those of single $Λ$ hypernuclei within an uniform parameterization.

nucl-th↗
arXiv2012

Quark deconfinement phase transition in nuclear matter for improved quark mass density-dependent model

The improved quark mass density-dependent (IQMDD) model, which has been successfully used to describe the properties of both infinite nuclear matter and finite nuclei, is applied to investigate the properties of quark deconfinement phase transition. By using the finite-temperature quantum field theory, we calculate the finite temperature effective potential and extend the IQMDD model to finite temperature and finite nuclear matter density. The critical temperature and the critical density of nuclear matter are given and the QCD phase diagram is addressed. It is shown that this model can not only describe the saturation properties of nuclear matter, but also explain the quark deconfinement phase transition successfully.

nucl-th↗
arXiv2012

Temporal evolution of tubular initial conditions and their influence on two-particle correlations in relativistic nuclear collisions

Relativistic nuclear collisions data on two-particle correlations exhibit structures as function of relative azimuthal angle and rapidity. A unified description of these near-side and away-side structures is proposed for low to moderate transverse momentum. It is based on the combined effect of tubular initial conditions and hydrodynamical expansion. Contrary to expectations, the hydrodynamics solution shows that the high energy density tubes (leftover from the initial particle interactions) give rise to particle emission in two directions and this is what leads to the various structures. This description is sensitive to some of the initial tube parameters and may provide a probe of the strong interaction. This explanation is compared with an alternative one where some triangularity in the initial conditions is assumed. A possible experimental test is suggested.

nucl-th↗
arXiv2010

Boost-invariant one-tube model for two-particle correlation

We show the in-plane/out-of-plane effect, in the two-particle correlation function, computed with the NexSPheRIO code, in Au+Au collisions at 200AGeV. In order to clarify the origin of the effect, a simplified model, which consists of a peripheral high-energy-density tube in a smooth background with longitudinal boost invariance, is applied.

hep-ph↗
arXiv2010

Fluctuating initial conditions in hydrodynamics for two-particle correlations

Event-by-event hydrodynamics, with fluctuating initial conditions, has shown to nicely reproduce several features of experimentally observed quantities in high-energy nuclear collisions. Here we discuss how it may help to understand, in a unified way, the various structures observed in the long-range two-particle correlations, both in nucleus-nucleus and p-p collisions. Suggestions of how experimentally this description could be tested are also discussed.

hep-ph↗
arXiv2009

Trying to understand the ridge effect in hydrodynamic model

In a recent paper, the hydrodynamic code NeXSPheRIO was used in conjunction with STAR analysis methods to study two-particle correlations as function of Delta_eta and Delta_phi. Both the ridge-like near-side and the double-hump away-side structures were obtained. However, the mechanism of ridge production was not clear. In order to understand it, we study a simple model with only one high-energy density peripheral tube in a smooth cylindrical back-ground, with longitudinal boost invariance. The results are rather surprising, but the model does produce the triple-ridge structure with one high ridge plus two lower ones placed symmetrically with respect to the former one. The shape of this structure is rather stable in a wide range of parameters.

hep-ph↗
arXiv2008

NeXSPheRIO results on azimuthal anisotropy in Au-Au collisions at 200A GeV

In this work, we present the results obtained by the hydrodynamic code NeXSPheRIO on anisotropic flows. In our calculation, we made use of event-by-event fluctuating initial conditions, and chemical freeze-out was explicitly implemented. We studied directed flow, elliptic flow and forth harmonic coefficient for various hadrons at different centrality windows for Au+Au collisions at 200 AGeV. The results are discussed and compared with experimental data from RHIC.

nucl-th↗
arXiv2007

NeXSPheRIO Results on Elliptic-Flow Fluctuations at RHIC

By using the NexSPheRIO code, we study the elliptic-flow fluctuations in Au+Au collisions at 200A GeV. It is shown that, by fixing the parameters of the model to correctly reproduce the charged pseudo-rapidity and the transverse-momentum distributions, reasonable agreement of with data is obtained, both as function of pseudo-rapidity as well as of transverse momentum, for charged particles. Our results on elliptic-flow fluctuations are in good agreement with the recently measured data in experiments.

hep-ph↗
arXiv2007

An approach to chemical freeze-out scenario of identified particle spectra at 200AGeV Au-Au collisions at RHIC

Thermal model fit indicates early chemical freeze-out of multi-strange hadrons with small collective velocities at 200AGeV Au-Au collisions at RHIC. In this work, we present our recent results by SPheRIO hydrodynamical calculations inspired by this picture. In our model, multi-strange hadrons go through chemical freeze-out when the system reaches some temperature close to the phase transition, stopping to make inelastic collisions, and their abundances are therefore determined only by partonic EOS. At a lower temperature thermal freeze-out takes place where elastic collisions are brought to a halt. We calculate the spectra for various hadrons at different centrality windows, with chemical and thermal freeze-out temperature being fit as a function of centrality. As it is shown, the result provides a reasonable panoramic description of the spectra of identified particles. Chemical freeze-out gives good correction of the multiplicity of certain species of particles, especially for multi-strange hadrons.

nucl-th↗
arXiv2007

Improved quark mass density- dependent model with quark-sigma meson and quark-omega meson couplings

An improved quark mass density- dependent model with the non-linear scalar sigma field and the $ω$-meson field is presented. We show that the present model can describe saturation properties, the equation of state, the compressibility and the effective nuclear mass of nuclear matter under mean field approximation successfully. The comparison of the present model and the quark-meson coupling model is addressed.

nucl-th↗
arXiv2007

Status and Promise of Particle Interferometry in Heavy-Ion Collisions

After five years of running at RHIC, and on the eve of the LHC heavy-ion program, we highlight the status of femtoscopic measurements. We emphasize the role interferometry plays in addressing fundamental questions about the state of matter created in such collisions, and present an enumerated list of measurements, analyses and calculations that are needed to advance the field in the coming years.

nucl-ex↗
arXiv2007

pT distribution of hyperons in 200A GeV Au-Au by smoothed particle hydrodynamics

The transverse momentum distributions for hadrons in 200GeV Au-Au collision at RHIC is calculated using a smoothed particle hydrodynamics code SPheRIO, and are compared with the data from STAR and PHOBOS Collaborations. By employing the equation of state which explicitly incorporate the strangeness conservation and introducing strangeness chemical potential into the code, the transverse spectrums give a reasonable description for the experimental data.

nucl-th↗