平野 哲文

We develop a framework of causal hydrodynamic fluctuations in onedimensional expanding system performing linearisation of the hydrodynamic equations around the boost invariant solution. Through the description of spacetime evolution of thermodynamic variables and flow velocity, we find a novel phenomenon that the structure of thermodynamic variables is almost frozen. We also show that two-particle correlation functions of final hadrons after freezeout are closely related with the mass of hadrons and properties of the medium such as viscosity, relaxation time and equation of state.

We develop a new dynamical model for high-energy heavy-ion collisions in the beam energy region of the highest net-baryon densities on the basis of nonequilibrium microscopic transport model JAM and macroscopic (3 + 1)-dimensional hydrodynamics by utilizing a dynamical initialization method. In this model, dynamical fluidization of a system is controlled by the source terms of the hydrodynamic fields. In addition, time-dependent core-corona separation of hot regions is implemented. We show that our new model describes multiplicities and mean transverse mass in heavy-ion collisions within a beam-energy region of 3 < root s(NN) < 30 GeV. Good agreement of the beam-energy dependence of the K+/pi(+) ratio is obtained, which is explained by the fact that a part of the system is not thermalized in our core-corona approach.

Anomalous hydrodynamics is a low-energy effective theory that captures effects of quantum anomalies. We develop a numerical code of ideal anomalous hydrodynamics and apply it to dynamics of heavy-ion collisions, where anomalous transports are expected to occur. We discuss implications of the simulations for possible experimental observations of anomalous transport effects. From analyses of the charge-dependent elliptic flow parameters (v(2)(+/-)) as a function of the net charge asymmetry A(+/-), we find that the linear dependence of Delta v1/2 v(2)(-) - v(2)(+) on the net charge asymmetry A(+/-) can come from a mechanism unrelated to anomalous transport effects. Instead, we find that a finite intercept Delta v(2)(+) (A(+/-) = 0) can come from anomalous effects. (C) 2017 The Author(s). Published by Elsevier B.V.

We employ a cutting-edge integrated dynamical model to quantify the effect of hydrodynamic fluctuations on the factorization ratio. Integrated dynamical model combines fully (3+1)-dimensional relativistic fluctuating hydrodynamics, Monte-Carlo version of the Glauber model as an event-by-event initialisation model of the hydrodynamic fields, and the hadronic cascade model in the late stage. By using this model, we first adjust initial parameters and transport coefficients to reproduce pseudorapidity distributions and transverse momentum dependence of elliptic flow parameter in Pb+Pb collisions at the LHC energy. We then analyse the factorization ratios in the longitudinal direction. By comparing results from fluctuating hydrodynamics, viscous hydrodynamics, and ideal hydrodynamics with experimental data, we quantify the effect of hydrodynamic fluctuations on the factorization ratio.

Recent observation of collective-flow-like behaviours in small colliding systems attracts significant theoretical and experimental interests. In large colliding systems, large collective flow has been interpreted as manifestation of almost perfect fluidity of the quark gluon plasma (QGP). So it is quite intriguing to explore how small the QGP can be as a fluid. Multiplicity fluctuations play a crucial role in centrality definition of the events in small colliding systems since the fluctuations are, in general, more important as the system size is getting smaller. To consider the correct multiplicity fluctuations, we employ PYTHIA which naturally describes multiplicity distribution in p+p collisions. We superpose p+p collisions by taking into account the number of participants and that of binary collisions from Monte-Carlo version of Glauber model and evaluate initial entropy density distributions which contain not only multiplicity fluctuations but also fluctuations of longitudinal profiles. Solving hydrodynamic equations followed by the hadronic afterburner, we calculate transverse momentum spectra, elliptic and triangular flow parameters in p+Au, d+Au and He-3+Au collisions at the RHIC energy and p+Pb collisions at the LHC energy. Although a large fraction of final anisotropic flow parameters comes from the fluid-dynamical stage, the effects of hadronic rescatterings turn out to be also important as well in understanding of the flow data in small colliding systems.

We propose a new approach to initialize the hydrodynamic fields, such as energy density distributions and four-flow velocity fields in hydrodynamic modeling of high-energy nuclear collisions at the collider energies. Instead of matching the energy-momentum tensor or putting the initial conditions of quark-gluon fluids at a fixed initial time, we utilize a framework of relativistic hydrodynamic equations with source terms to describe the initial stage. Putting the energy and momentum loss rate of the initial partons into the source terms, we obtain hydrodynamic initial conditions dynamically. The resultant initial profile of the quark-gluon fluid looks highly bumpy as seen in the conventional event-by-event initial conditions. In addition, initial random flow velocity fields also are generated as a consequence of momentum deposition from the initial partons. We regard the partons that survive after the dynamical initialization process as the mini-jets and find sizable effects of both mini-jet propagation in the quark-gluon fluids and initial random transverse flow on the final momentum spectra and anisotropic flow observables. We perform event-by-event (3+1)-dimensional ideal hydrodynamic simulations with this new framework that enables us to describe the hydrodynamic bulk collectivity, parton energy loss, and interplay among them in a unified manner.

We propose a new approach to initialize the hydrodynamic fields, such as energy density distributions and four-flow velocity fields in hydrodynamic modeling of high-energy nuclear collisions at the collider energies. Instead of matching the energy-momentum tensor or putting the initial conditions of quark-gluon fluids at a fixed initial time, we utilize a framework of relativistic hydrodynamic equations with source terms to describe the initial stage. Putting the energy and momentum loss rate of the initial partons into the source terms, we obtain hydrodynamic initial conditions dynamically. The resultant initial profile of the quark-gluon fluid looks highly bumpy as seen in the conventional event-by-event initial conditions. In addition, initial random flow velocity fields also are generated as a consequence of momentum deposition from the initial partons. We regard the partons that survive after the dynamical initialization process as the mini-jets and find sizable effects of both mini-jet propagation in the quark-gluon fluids and initial random transverse flow on the final momentum spectra and anisotropic flow observables. We perform event-by-event (3+1)-dimensional ideal hydrodynamic simulations with this new framework that enables us to describe the hydrodynamic bulk collectivity, parton energy loss, and interplay among them in a unified manner.

By using a hybrid dynamical model which describes space-time evolution of the bulk medium, (mini-)jet propagation and interactions between medium and (mini) jets, we study hydrodynamic responses to (mini-)jet propagation in high energy nuclear collisions. When an energetic jet traverses the bulk matter, it loses its energy into the matter and forms a Mach-cone like structure. On the other hand, the bulk matter expands radially due to pressure gradient. As a result, there happens an interplay between radial expansion and the Mach cone. We discuss possible phenomena and observables related with this in asymmetric gamma-jet events. We also discuss phenomena in which many mini-jets propagate the bulk matter at once in an event and calculate higher harmonics of azimuthal angle distribution.

We investigate collectivity in small colliding systems by using an integrated dynamical model in which Monte-Carlo initialisation of hydrodynamic fields, the ideal hydrodynamic description of the quark-gluon plasma and the kinetic description of the hadron gas are incorporated. We implement fluctuations of the multiplicity and of the longitudinal matter profile in the initial conditions which are of particular importance in small colliding systems. We also discuss the effects of hadronic rescatterings on flow observables.

We develop a new integrated dynamical model to investigate the effects of the hydrodynamic fluctuations on observables in high-energy nuclear collisions. We implement hydrodynamic fluctuations in a fully 3-D dynamical model consisting of the hydrodynamic initialization models of the Monte-Carlo Kharzeev-Levin-Nardi model, causal dissipative hydrodynamics and the subsequent hadronic cascades. By analyzing the hadron distributions obtained by massive event-by-event simulations with both of hydrodynamic fluctuations and initial-state fluctuations, we discuss the effects of hydrodynamic fluctuations on the flow harmonics, v(n) and their fluctuations.

We report on our recent attempt of quantitative modeling of the Chiral Magnetic Effect (CME) in heavy-ion collisions. We perform 3+1 dimensional anomalous hydrodynamic simulations on an event-by-event basis, with constitutive equations that contain the anomaly-induced effects. We also develop a model of the initial condition for the axial charge density that captures the statistical nature of random chirality imbalances created by the color flux tubes. Basing on the event-by-event hydrodynamic simulations for hundreds of thousands of collisions, we calculate the correlation functions that are measured in experiments, and discuss how the anomalous transport affects these observables.

We study effects of the hadronic rescattering on final observables especially for multi-strange hadrons such as phi, Xi and Omega in high-energy heavy-ion collisions within an integrated dynamical approach. In this approach, (3+1)-dimensional ideal hydrodynamics is combined with a microscopic transport model, JAM. We simulate the collisions with or without hadronic rescatterings and compare observables between these two options so that we quantify the effects of the hadronic rescattering. We find that the mean transverse momentum and the elliptic flow parameter of multi-strange hadrons are less affected by hadronic rescattering and, as a result, the mass ordering of the p(T)-differential elliptic flow parameter v(2)(p(T)) is violated: At the RHIC and the LHC energies the v(2)(p(T)) for phi-mesons is larger than that for protons in the low-p(T) regions.

We study the hydrodynamic response to jet propagation in the expanding QGP and investigate how the particle spectra after the hydrodynamic evolution of the QGP reflect it. We perform simulations of the space-time evolution of the QGP in gamma-jet events by solving (3+1)-dimensional ideal hydrodynamic equations with source terms. Mach cone is induced by the jet energy deposition and pushes back the radial flow of the expanding background. Especially in the case when the jet passage is off-central one, the number of particles emitted in the direction of the push back decreases. This is the signal including the information about the formation of the Mach cone and the jet passage in the QGP fluid.

We investigate effects of causal hydrodynamic fluctuations in the longitudinally expanding quark gluon plasma on final entropy distributions in high-energy nuclear collisions.

We study the hydrodynamic excitation by jets in QGP and the consequent particle spectra. Events with jets through the QGP in heavy-ion collisions are simulated by solving (3+1)-dimensional ideal hydrodynamic equations with source terms. Mach cone is formed and develops in the expanding medium. Especially in the case where jets travel through the off-central passage, the Mach cone directionally pushes back the radial flow of the background. As the result, the number of particles emitted in the direction of the push back decreases. This can be a direct signal of hydrodynamic excitation by jets and includes the information about the jet passage in the QGP medium.

We study the hydrodynamic response to jet quenching in expanding quark-gluon plasma (QGP) and its signal in the resulting particle distribution. The ideal hydrodynamic simulations of the gamma-jet events in heavy-ion collisions are performed in a full (3 + 1)-dimensional setup. The jet-induced Mach cone and the radial expansion of the background mutually push and distort each other. As a result, the particle emission is suppressed in the direction in which the radial flow is pushed back by the Mach cone when the jet path is an off-central one. This is the direct signal of hydrodynamic response to the jet and, moreover, includes information about the jet path in the expanding QGP fluid.

We study the effects of hadronic rescattering on hadron distributions in high-energy nuclear collisions by using an integrated dynamical approach. This approach is based on a hybrid model combining (3+1)-dimensional ideal hydrodynamics for the quark gluon plasma (QGP) and a transport model for the hadron resonance gas. Since the hadron distributions are the result of the entire expansion history of the system, understanding the QGP properties requires investigating how rescattering during the hadronic stage affects the final distributions of hadrons. We include multistrange hadrons in our study and quantify the effects of hadronic rescattering on their mean transverse momenta and elliptic flow. We find that multistrange hadrons scatter less during the hadronic stage than nonstrange particles, and thus their distributions reflect the properties of the system in an earlier stage than the distributions of nonstrange particles.

We study the effects of hadronic rescattering on hadron distributions in high-energy nuclear collisions by using an integrated dynamical approach. This approach is based on a hybrid model combining (3+ 1)-dimensional ideal hydrodynamics for the quark gluon plasma (QGP) and a transport model for the hadron resonance gas. Since the hadron distributions are the result of the entire expansion history of the system, understanding the QGP properties requires investigating how rescattering during the hadronic stage affects the final distributions of hadrons. We include multistrange hadrons in our study and quantify the effects of hadronic rescattering on their mean transverse momenta and elliptic flow. We find that multistrange hadrons scatter less during the hadronic stage than nonstrange particles, and thus their distributions reflect the properties of the system in an earlier stage than the distributions of nonstrange particles.

We study the collective flow of the QGP-fluid which transports the energy and momentum deposited from jets. Simulations of the propagation of jets together with expansion of the QGP-fluid are performed by solving relativistic hydrodynamic equations numerically in the fully (3 + 1)-dimensional space. Mach cones are induced by the energy momentum deposition from jets and extended by the expansion of the QGP. As a result, low-P-T particles are enhanced at large angles from the jet axis. This provedes an intimate link between the observables in di-jet asymmetric events in heavy-ion collisions and theoretical pictures of the medium excitation by jet-energy deposition. (c) 2014 Elsevier B.V. All rights reserved.

We discuss multiplicity fluctuation caused by noises during hydrodynamic evolution of the quark-gluon fluid created in high-energy nuclear collisions. (C) 2014 Elsevier B.V. All rights reserved.

We show that in asymmetric heavy-ion collisions, especially off-central Cu + Au collisions, a sizable strength of electric field directed from Au nucleus to Cu nucleus is generated in the overlapping region, because of the difference in the number of electric charges between the two nuclei. This electric field would induce an electric current in the matter created after the collision, which results in a dipole deformation of the charge distribution. The directed flow parameters v1± of charged particles turn out to be sensitive to the charge dipole and provide us with information about electric conductivity of the quark gluon plasma. © 2014 American Physical Society.

We study the transport dynamics of momenta deposited from jets in ultrarelativistic heavy-ion collisions. Assuming that the high-energy partons traverse expanding quark-gluon fluids and are subject to lose their energy and momentum, we simulate dijet asymmetric events by solving relativistic hydrodynamic equations numerically without linearization in the fully (3+1)-dimensional coordinate. Mach cones are formed and strongly broadened by radial flow of the background medium. As a result, the yield of low-pT particles increases at large angles from the jet axis and compensates the dijet momentum imbalance inside the jet cone. This provides an intimate link between the medium excitation by jets and results in dijet asymmetric events observed by the CMS Collaboration. © 2014 American Physical Society.

We study the transport dynamics of momenta deposited from jets in ultrarelativistic heavy-ion collisions. Assuming that the high-energy partons traverse expanding quark-gluon fluids and are subject to lose their energy and momentum, we simulate dijet asymmetric events by solving relativistic hydrodynamic equations numerically without linearization in the fully (3 + 1)-dimensional coordinate. Mach cones are formed and strongly broadened by radial flow of the background medium. As a result, the yield of low-pT particles increases at large angles from the jet axis and compensates the dijet momentum imbalance inside the jet cone. This provides an intimate link between the medium excitation by jets and results in dijet asymmetric events observed by the CMS Collaboration.

We show that in asymmetric heavy-ion collisions, especially off-central Cu + Au collisions, a sizable strength of electric field directed from Au nucleus to Cu nucleus is generated in the overlapping region, because of the difference in the number of electric charges between the two nuclei. This electric field would induce an electric current in the matter created after the collision, which results in a dipole deformation of the charge distribution. The directed flow parameters upsilon(+/-)(1) of charged particles turn out to be sensitive to the charge dipole and provide us with information about electric conductivity of the quark gluon plasma.

In this review, I show a personal overview of theoretical results presented in the International Conference on the Initial Stages in High-Energy Nuclear Collision, in Illa da Toxa, Galicia, Spain, Sept. 8-14, 2013. (C) 2014 Elsevier B.V. All rights reserved.

We study dynamics of a QGP fluid induced by energetic partons propagating through it. We construct a (3+1)-dimensional QGP-fluid+Jet model. When a jet traverses a uniform fluid, it induces a Mach cone structure of energy density distribution and a vortex ring surrounding a path of the jet. When a pair of jets travels through a radially expanding fluid, low momentum particles are dominantly induced at large angles from the quenched jet. This result is qualitatively consistent with observation of the CMS Collaboration at LHC.

We review integrated dynamical approaches to describe heavy ion reaction as a whole at ultrarelativistic energies. Since final observables result from all the history of the reaction, it is important to describe all the stages of the reaction to obtain the properties of the quark-gluon plasma from experimental data. As an example of these approaches, we develop an integrated dynamical model, which is composed of a fully (3 + 1) dimensional ideal hydrodynamic model with a state-of-the-art equation of state based on lattice QCD, and subsequent hadronic cascade in the late stage. Initial conditions are obtained employing Monte Carlo versions of the Kharzeev-Levin-Nardi model (MC-KLN) or the Glauber model (MC-Glauber). Using this integrated model, we first simulate relativistic heavy ion collisions at the RHIC and LHC energies starting from conventional smooth initial conditions. We next utilise each Monte Carlo sample of initial conditions on an event-by-event basis and perform event-by-event dynamical simulations to accumulate a large number of minimum bias events. A special attention is paid to performing the flow analysis as in experiments towards consistent comparison of theoretical results with experimental data. (C) 2013 Elsevier B.V. All rights reserved.

The physics of quark gluon plasma (QGP) and heavy ion collisions at the collider energies is briefly reviewed. We first discuss about the discovery of a nearly perfect fluidity of the QGP. We also highlights recent topics on responses of the QGP to initial deformation and propagation of a jet

The NA60 Collaboration has extracted the inverse slope parameters, T-eff of the di-muon spectra originating from the In + In collisions at root s(NN) = 17.3 GeV for various invariant mass regions. They have observed that the inverse slope parameter as a function of invariant mass of the lepton pair drops beyond the rho peak. In the present work, first we reproduce the observed invariant mass and transverse momentum spectra of the muon pairs by taking into account the medium effects on the hadronic spectral function. Then we show that the slope parameters extracted from the transverse momentum distributions for various invariant mass windows can be explained by assuming the formation of a partonic phase initially which reverts to the hadronic phase through a weak first-order phase transition at a temperature T-c similar to 175 MeV. It is observed that a scenario without the formation of a partonic phase does not reproduce the nonmonotonic behavior of the inverse slope parameter nontypical of radial flow.

We attempt to understand the low-mass dielectron enhancement observed by the PHENIX Collaboration at the Relativistic Heavy Ion Collider by transport peak in the spectral function. On the basis of the second-order formalism of relativistic dissipative hydrodynamics, we parametrize the spectral function in low-frequency and long-wavelength regions by two transport coefficients, electric diffusion coefficient D and relaxation time tau(J), and compare our theoretical dielectron spectra with the experimental data. We study the spectrum of dielectrons produced in relativistic heavy-ion collisions by using the profile of matter evolution under full ( 3 + 1)-dimensional hydrodynamics. We find that the experimental data require the diffusion coefficient to be D &gt;= 2/T, with T being temperature. Our analysis shows that dielectrons emitted through the transport process mainly come from the high-temperature quark-gluon plasma phase.