arXiv subjects

Yu. B. Ivanov

Publications and source records attributed to Yu. B. Ivanov.

At least 55 records · Page 3Linked to original sources

arXiv2014

Alternative Scenarios of Relativistic Heavy-Ion Collisions: III. Transverse Momentum Spectra

Transverse-mass spectra, their inverse slopes and mean transverse masses in relativistic collisions of heavy nuclei are analyzed in a wide range of incident energies 2.7 GeV $\le \sqrt{s_{NN}}\le$ 39 GeV. The analysis is performed within the three-fluid model employing three different equations of state (EoS's): a purely hadronic EoS, an EoS with the first-order phase transition and that with a smooth crossover transition into deconfined state. Calculations show that inverse slopes and mean transverse masses of all the species (with the exception of antibaryons within the hadronic scenario) exhibit a step-like behavior similar to that observed for mesons and protons in available experimental data. This step-like behavior takes place for all considered EoS's and results from the freeze-out dynamics rather than is a signal of the deconfinement transition. A good reproduction of experimental inverse slopes and mean transverse masses for light species (up to proton) is achieved within all the considered scenarios. The freeze-out parameters are precisely the same as those used for reproduction of particles yields in previous papers of this series. This became possible because the freeze-out stage is not completely equilibrium.

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arXiv2013

Phase Evolution and Freeze-out within Alternative Scenarios of Relativistic Heavy-Ion Collisions

Global evolution of the matter in relativistic collisions of heavy nuclei and the resulting global freeze-out parameters are analyzed in a wide range of incident energies 2.7 GeV $\le \sqrt{s_{NN}}\le$ 39 GeV. The analysis is performed within the three-fluid model employing three different equations of state (EoS): a purely hadronic EoS, an EoS with the first-order phase transition and that with a smooth crossover transition. Global freeze-out parameters deduced from experimental data within the statistical model are well reproduced within the crossover scenario. The 1st-order-transition scenario is slightly less successful. The worst reproduction is found within the purely hadronic scenario. These findings make a link between the EoS and results of the statistical model, and indicate that deconfinement onset occurs at $\sqrt{s_{NN}}\gsim$ 5 GeV.

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arXiv2013

Non-Equilibrium 2PI Potential and Its Possible Application to Evaluation of Bulk Viscosity

Within non-equilibrium Green's function technique on the real-time contour and the two-particle-irreducable (2PI) $Φ$-functional method, a non-equilibrium potential is introduced. It naturally generalizes the conventional thermodynamic potential with which it coincides in thermal equilibrium. Variations of the non-equilibrium potential over respective parameters result in the same quantities as those of the thermodynamic potential but in arbitrary non-equilibrium. In particular, for slightly non-equilibrium inhomogeneous configurations a variation of the non-equilibrium potential over volume is associated with the trace of the non-equilibrium stress tensor. The latter is related to the bulk viscosity. This provides a novel way for evaluation of the bulk viscosity.

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arXiv2013

Alternative Scenarios of Relativistic Heavy-Ion Collisions: II. Particle Production

Particle production in relativistic collisions of heavy nuclei is analyzed in a wide range of incident energies 2.7 GeV $\le \sqrt{s_{NN}}\le$ 62.4 GeV. The analysis is performed within the three-fluid model employing three different equations of state (EoS): a purely hadronic EoS, an EoS with the first-order phase transition and that with a smooth crossover transition. It is found that the hadronic scenario fails to reproduce experimental yields of antibaryons (strange and nonstrange), starting already from lower SPS energies, i.e. $\sqrt{s_{NN}}>$ 5 GeV. Moreover, at energies above the top SPS one, i.e. $\sqrt{s_{NN}}>$ 17.4 GeV, the mid-rapidity densities predicted by the hadronic scenario considerably exceed the available RHIC data on all species. At the same time the deconfinement-transition scenarios reasonably agree (to a various extent) with all the data. The present analysis demonstrates certain advantage of the deconfinement-transition EoS's. However, all scenarios fail to reproduce the strangeness enhancement in the incident energy range near 30A GeV (i.e. a horn anomaly in the $K^+/π^+$ ratio) and yields of $ϕ$-mesons at 20A--40A GeV.

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arXiv2013

Elliptic Flow of Protons and Antiprotons in Au+Au Collisions at $\sqrt{s_{NN}}$ = 7.7--62.4 GeV within Alternative Scenarios of Three-Fluid Dynamics

Analysis of elliptic flow of protons and antiprotons in Au+Au collisions is performed in a wide range of incident energies $\sqrt{s_{NN}}$ = 7.7--62.4 GeV. Simulations has been done within the three-fluid model employing a purely hadronic equation of state (EoS) and two versions of the EoS involving deconfinement transition: an EoS with the first-order phase transition and that with a smooth crossover transition. It is found that the proton data are reproduced approximately to the same extent within all of the scenarios, including the hadronic one, while the deconfinement scenarios look certainly preferable for the antiproton elliptic flow. The fact that difference between elliptic flows of protons and antiprotons decreases with the incident energy rise is a consequence of reducing baryon stopping rather than an onset of deconfinement.

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arXiv2013

Alternative Scenarios of Relativistic Heavy-Ion Collisions: I. Baryon Stopping

Simulations of relativistic heavy-ion collisions within the three-fluid model employing a purely hadronic equation of state (EoS) and two versions of the EoS involving deconfinement transition are presented. The latter are an EoS with the first-order phase transition and that with a smooth crossover transition. The model setup is described in detail. The analysis is performed in a wide range of incident energies 2.7 GeV $< \sqrt{s_{NN}} <$ 39 GeV in terms of the center-of-mass energy. Results on proton and net-proton rapidity distributions are reported. Comparison with available data indicate certain preference of the crossover EoS. It is found that predictions within deconfinement-transition scenarios exhibit a "peak-dip-peak-dip" irregularity in the incident energy dependence of the form of the net-proton rapidity distributions in central collisions. This irregularity is a signal of deconfinement onset occurring in the hot and dense stage of the nuclear collision.

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arXiv2013

Baryon Stopping as a Probe of Deconfinement Onset in Relativistic Heavy-Ion Collisions

It is argued that an irregularity in the baryon stopping is a natural consequence of a phase transition occurring in the compression stage of a nuclear collision. It is a combined effect of the softest point inherent in an equation of state (EoS) with a phase transition and a change in the nonequilibrium dynamics from hadronic to partonic transport. Thus, this irregularity is a signal from a hot and dense stage of the nuclear collision. In order to illustrate this proposition, calculations within the three-fluid model were performed with three different EoS's: a purely hadronic EoS, an EoS with a first-order phase transition and that with a smooth crossover transition. It is found that predictions within the first-order-transition scenario indeed reveal an a strong irregularity in the incident energy dependence of the form of the net-proton rapidity distributions in central collisions. This behavior is in contrast to that for the hadronic scenario, where the distribution form gradually evolve, displaying no irregularity. The case of the crossover EoS is intermediate. Only a weak irregularity takes place. Experimental data also exhibit a trend of similar irregularity, which is however based on still preliminary data at energies of 20A GeV and 30A GeV.

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arXiv2013

Color path-integral Monte-Carlo simulations of quark-gluon plasma: Thermodynamic and transport properties

Based on the quasiparticle model of the quark-gluon plasma (QGP), a color quantum path-integral Monte-Carlo (PIMC) method for calculation of thermodynamic properties and -- closely related to the latter -- a Wigner dynamics method for calculation of transport properties of the QGP are formulated. The QGP partition function is presented in the form of a color path integral with a new relativistic measure instead of the Gaussian one traditionally used in the Feynman-Wiener path integral. It is shown that the PIMC method is able to reproduce the lattice QCD equation of state at zero baryon chemical potential at realistic model parameters (i.e. quasiparticle masses and coupling constant) and also yields valuable insight into the internal structure of the QGP. Our results indicate that the QGP reveals quantum liquid-like (rather than gas-like) properties up to the highest considered temperature of 525 MeV. The pair distribution functions clearly reflect the existence of gluon-gluon bound states, i.e. glueballs, at temperatures just above the phase transition, while meson-like $q\bar{q}$ bound states are not found. The calculated self-diffusion coefficient agrees well with some estimates of the heavy-quark diffusion constant available from recent lattice data and also with an analysis of heavy-quark quenching in experiments on ultrarelativistic heavy ion collisions, however, appreciably exceeds other estimates. The lattice and heavy-quark-quenching results on the heavy-quark diffusion are still rather diverse. The obtained results for the shear viscosity are in the range of those deduced from an analysis of the experimental elliptic flow in ultrarelativistic heavy ions collisions, i.e. in terms the viscosity-to-entropy ratio, $1/4π< η/S < 2.5/4π$, in the temperature range from 170 to 440 MeV.

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arXiv2012

Color path-integral Monte Carlo simulations of quark-gluon plasma

Thermodynamic properties of a strongly coupled quark-gluon plasma (QGP) of constituent quasiparticles are studied by a color path-integral Monte Carlo simulations (CPIMC). For our simulations we have presented QGP partition function in the form of color path integral with new relativistic measure instead of Gaussian one used in Feynman and Wiener path integrals. For integration over color variable we have also developed procedure of sampling color variables according to the group SU(3) Haar measure. It is shown that this method is able to reproduce the available quantum lattice chromodynamics (QCD) data.

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arXiv2011

Quantum simulations of thermodynamic properties of strongly coupled quark-gluon plasma

A strongly coupled quark-gluon plasma (QGP) of heavy constituent quasi-particles is studied by a path-integral Monte-Carlo method. This approach is a quantum generalization of the model developed by Gelman, Shuryak and Zahed. It is shown that this method is able to reproduce the QCD lattice equation of state and also yields valuable insight into the internal structure of the QGP. The results indicate that the QGP reveals liquid-like rather than gas-like properties. At temperatures just above the critical one it was found that bound quark-antiquark states still survive. These states are bound by effective string-like forces and turns out to be colorless. At the temperature as large as twice the critical one no bound states are observed. Quantum effects turned out to be of prime importance in these simulations.

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arXiv2011

Baryon stopping as a signal of the mixed phase onset

It is argued that the experimentally observed baryon stopping indicates a non-monotonous behaviour as a function of the incident energy of colliding nuclei. This can be quantified by a midrapidity reduced curvature of the net-proton rapidity spectrum and reveals itself as a zigzag irregularity in the excitation function of this curvature. The three-fluid dynamic calculations with a hadronic equation of state (EoS) fail to reproduce this irregularity. At the same time, the same calculations with an EoS involving a first-order phase transition and a crossover one into the quark-gluon phase do reproduce this zigzag behaviour, however only qualitatively.

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arXiv2010

Quantum simulations of strongly coupled quark-gluon plasma

A strongly coupled quark-gluon plasma (QGP) of heavy constituent quasiparticles is studied by a path-integral Monte-Carlo method, which improves the corresponding classical simulations by extending them to the quantum regime. It is shown that this method is able to reproduce the lattice equation of state and also yields valuable insight into the internal structure of the QGP. The results indicate that the QGP reveals liquid-like rather than gas-like properties. At temperatures just above the critical one it was found that bound quark-antiquark states still survive. These states are bound by effective string-like forces. Quantum effects turned out to be of prime importance in these simulations.

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arXiv2010

Baryon Stopping in Heavy-Ion Collisions at E_{lab}= 2--160 GeV/nucleon

It is argued that the experimentally observed baryon stopping may indicate (within the present experimental uncertainties) a non-monotonous behaviour as a function of the incident energy of colliding nuclei. This can be quantified by a midrapidity reduced curvature of the net-proton rapidity spectrum. The above non-monotonous behaviour reveals itself as a "zig-zag" irregularity in the excitation function of this curvature. The three-fluid dynamic calculations with a hadronic equation of state (EoS) fail to reproduce this irregularity. At the same time, the same calculations with an EoS involving a first-order phase transition into the quark-gluon phase do reproduce this "zig-zag" behaviour, however only qualitatively.

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arXiv2009

Elliptic Flow and Dissipation in Heavy-Ion Collisions at E_{lab} = (1--160)A GeV

Elliptic flow in heavy-ion collisions at incident energies $E_{lab}\simeq$ (1--160)A GeV is analyzed within the model of 3-fluid dynamics (3FD). We show that a simple correction factor, taking into account dissipative affects, allows us to adjust the 3FD results to experimental data. This single-parameter fit results in a good reproduction of the elliptic flow as a function of the incident energy, centrality of the collision and rapidity. The experimental scaling of pion eccentricity-scaled elliptic flow versus charged-hadron-multiplicity density per unit transverse area turns out to be also reasonably described. Proceeding from values of the Knudsen number, deduced from this fit, we estimate the upper limit the shear viscosity-to-entropy ratio as $η/s \sim 1-2$ at the SPS incident energies. This value is of the order of minimal $η/s$ observed in water and liquid nitrogen.

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arXiv2009

Nonlocal Form of Quantum Off-Shell Kinetic Equation

A new nonlocal form of the off-shell kinetic equation is derived. While being equivalent to the Kadanoff--Baym and Botermans--Malfliet formulations in the range of formal applicability, it has certain advantages beyond this range. It possesses more accurate conservation laws for Noether quantities than those in the Botermans--Malfliet formulation. At the same time the nonlocal form, similarly to the Botermans--Malfliet one, allows application of the test-particle method for its numerical solution, which makes it practical for simulations of heavy-ion collisions. The physical meaning of the time-space nonlocality is clarified.

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arXiv2008

On freeze-out problem in relativistic hydrodynamics

A finite unbound system which is equilibrium in one reference frame is in general nonequilibrium in another frame. This is a consequence of the relative character of the time synchronization in the relativistic physics. This puzzle was a prime motivation of the Cooper--Frye approach to the freeze-out in relativistic hydrodynamics. Solution of the puzzle reveals that the Cooper--Frye recipe is far not a unique phenomenological method that meets requirements of energy-momentum conservation. Alternative freeze-out recipes are considered and discussed.

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arXiv2008

Transverse-Mass Spectra in Heavy-Ion Collisions at energies E_{lab} = 2--160 GeV/nucleon

Transverse-mass spectra of protons, pions and kaons produced in collisions of heavy nuclei are analyzed within the model of 3-fluid dynamics. It was demonstrated that this model consistently reproduces these spectra in wide ranges of incident energies E_{lab}, from 4A GeV to 160A GeV, rapidity bins and centralities of the collisions. In particular, the model describes the "step-like" dependence of kaon inverse slopes on the incident energy. The key point of this explanation is interplay of hydrodynamic expansion of the system with its dynamical freeze-out.

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arXiv2008

Transverse-Mass Effective Temperature in Heavy-Ion Collisions from AGS to SPS

Transverse-mass spectra in Au+Au and Pb+Pb collisions in incident energy range from 2A to 160A GeV are analyzed within the model of 3-fluid dynamics. It is shown that dynamical description of freeze-out, accepted in this model, naturally explains the incident energy behavior of inverse-slope parameters of these spectra observed in experiment. Simultaneous reproduction of the inverse-slopes of all considered particles (protons, pions and kaons) suggests that these particles belong to the same hydrodynamic flow at the instant of their freeze-out.

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