arXiv subjects

Yu. B. Ivanov

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

At least 73 records · Page 4Linked to original sources

arXiv2007

What we have learned so far from 3-fluid hydrodynamics

Available data on heavy-ion collisions at AGS and SPS energies are analyzed using a 3-fluid dynamical model within a purely hadronic scenario. We investigate the problems met in reproducing these data within this scheme. In particular, we try to indicate those data which could point towards the occurrence of a phase transition into the quark-gluon phase. We also discuss the success of the model in reproducing the transverse-mass spectra of various hadrons. We argue that the simultaneous reproduction of the inverse-slope parameters of all considered particles may imply that these particles belong to the same hydrodynamic flow at the instant of their freeze-out rather than that it signals the onset of a phase transition.

nucl-th↗

arXiv2007

Dynamical Freeze-out in 3-Fluid Hydrodynamics

Freeze-out procedure accepted in the model of 3-fluid dynamics (3FD) is analyzed. This procedure is formulated in terms of drain terms in hydrodynamic equations. Dynamics of the freeze-out is illustrated by 1-dimensional simulations. It is demonstrated that the resulting freeze-out reveals a nontrivial dynamics depending on initial conditions in the expanding ``fireball''. The freeze-out front is not defined just ``geometrically'' on the condition of the freeze-out criterion met but rather is a subject the fluid evolution. It competes with the fluid flow and not always reaches the place where the freeze-out criterion is met. Dynamics of the freeze-out in 3D simulations is analyzed. It is demonstrated that the late stage of central nuclear collisions at top SPS energies is of the form of three (two baryon-rich and one baryon-free) fireballs separated from each other.

nucl-th↗

arXiv2006

Dynamical phase trajectories for relativistic nuclear collisions

Central collisions of gold nuclei are simulated by several existing models and the central net baryon density rho and the energy density eps are extracted at successive times, for beam kinetic energies of 5-40 GeV per nucleon. The resulting trajectories in the (rho,eps) phase plane are discussed from the perspective of experimentally exploring the expected first-order hadronization phase transition with the planned FAIR at GSI or in a low-energy campaign at RHIC.

nucl-th↗

arXiv2006

Collective Flow in Heavy-Ion Collisions from AGS to SPS

Collective transverse flow in heavy-ion collisions at incident energies E_{lab} = (1 -160)A GeV is analyzed within the model of 3-fluid dynamics (3FD). Simulations are performed with purely hadronic equation of state (EoS). At the AGS energies the flow turns out to be sensitive to the stopping power of nuclear matter rather than only to the stiffness of the EoS. When the stopping power is fixed to reproduce other observables, the flow data favor more and more soft EoS with the incident energy rise, which can be associated with ``a transition from hadronic to string matter'' reported in the Hadron-String-Dynamics (HSD) model. Problems, which are met in simultaneous reproduction of directed and elliptic flows within the 3FD, suggest that the transverse flow is very sensitive to the character of the transverse-momentum nonequilibrium at the initial stage of collision. Arguments in favor of "early-stage" nature of the flow observable are put forward. This suggests that the flow (especially the directed one) is determined by early-stage evolution of the collision rather than freeze-out stage.

nucl-th↗

arXiv2006

Relativistic Heavy-Ion Collisions within 3-Fluid Hydrodynamics: Hadronic Scenario

A 3-fluid hydrodynamic model for simulating relativistic heavy-ion collisions is introduced. Alongside with two baryon-rich fluids, the new model considers time-delayed evolution of a third, baryon-free (i.e. with zero net baryonic charge) fluid of newly produced particles. Its evolution is delayed due to a formation time, during which the baryon-free fluid neither thermalizes nor interacts with the baryon-rich fluids. After the formation it starts to interact with the baryon-rich fluids and quickly gets thermalized. Within this model with pure hadronic equation of state, a systematic analysis of various observables at incident energies between few and about 160A GeV has been done as well as comparison with results of transport models. We have succeeded to reasonably reproduce a great body of experimental data in the incident energy range of E_{lab} = (1-160)A GeV. The list includes proton and pion rapidity distributions, proton transverse-mass spectra, rapidity distributions of Lambda and antiLambda hyperons, elliptic flow of protons and pions (with the exception of proton v2 at 40A GeV), multiplicities of pions, positive kaons, phi-mesons, hyperons and antihyperons, including multi-strange particles. This agreement is achieved on the expense of substantial enhancement of the interflow friction as compared to that estimated proceeding from hadronic free cross sections. However, we have also found out certain problems. The calculated yield of K^- is approximately by a factor of 1.5 higher than that in the experiment. We have also failed to describe directed transverse flow of protons and pion at E_{lab} > 40A GeV. This failure apparently indicates that the used EoS is too hard and thereby leaves room for a phase transition.

nucl-th↗

arXiv2005

Dynamics of Resonances in Strongly Interacting Systems

The effects of the propagation of particles which have a finite life-time and an according broad distribution in their mass spectrum are discussed in the context of a transport descriptions. In the first part some example cases of mesonic modes in nuclear matter at finite densities and temperatures are presented. These equilibrium calculations illustrate the dynamical range of spectral distributions to be adequately covered by non-equilibrium description of the dynamics of two nuclei colliding at high energies. The second part addresses the problem of transport descriptions which properly account for the damping width of the particles. A systematic and general gradient approximation is presented in the form of diagrammatic rules which permit to derive a self-consistent transport scheme from the Kadanoff--Baym equation. The scheme is conserving and thermodynamically consistent provided the self-energies are obtained within the Phi-derivable two-particle irreducible (2PI) method of Baym. The merits, the limitations and partial cures of the limitations of this transport scheme are discussed in detail.

nucl-th↗

arXiv2005

Renormalization of a gapless Hartree-Fock approximation to a theory with spontaneously broken O(N)-symmetry

The renormalization of a gapless Phi-derivable Hartree--Fock approximation to the O(N)-symmetric lambda*phi^4 theory is considered in the spontaneously broken phase. This kind of approach was proposed by three of us in a previous paper in order to preserve all the desirable features of Phi-derivable Dyson-Schwinger resummation schemes (i.e., validity of conservation laws and thermodynamic consistency) while simultaneously restoring the Nambu--Goldstone theorem in the broken phase. It is shown that unlike for the conventional Hartree--Fock approximation this approach allows for a scale-independent renormalization in the vacuum. However, the scale dependence still persists at finite temperatures. Various branches of the solution are studied. The occurrence of a limiting temperature inherent in the renormalized Hartree--Fock approximation at fixed renormalization scale mu is discussed.

hep-ph↗

arXiv2005

Lattice QCD Constraints on Hybrid and Quark Stars

A QCD-motivated dynamical-quasiparticle model with parameters adjusted to reproduce the lattice-QCD equation of state is extrapolated from region of high temperatures and moderate baryonic densities to the domain of high baryonic densities and zero temperature. The resulting equation of state matched with realistic hadronic equations of state predicts a phase transition into the quark phase at higher densities than those reachable in neutron star interiors. This excludes the possibility of the existence of hybrid (hadron-quark) stars. Pure quark stars are possible and have low masses, small radii and very high central densities. Similar results are obtained for a simple bag model with massive quarks, fitted to reproduce the same lattice results. Self-bound quark matter is also excluded within these models. Uncertainties in the present extrapolation re discussed. Comparison with standard bag models is made.

astro-ph↗

arXiv2005

Gapless Hartree-Fock Resummation Scheme for the O(N) Model

A modified selfconsistent Hartree-Fock approximation to the lambda*phi^4 theory with spontaneously broken O(N) symmetry is proposed. It preserves all the desirable features, like conservation laws and thermodynamic consistency, of the selfconsistent Dyson scheme generated from a 2PI functional, also known as the Phi-derivable scheme, while simultaneously respecting the Nambu-Goldstone theorem in the chiral-symmetry broken phase. Various approximate resummation schemes are discussed.

hep-ph↗

arXiv2004

Equation of state of deconfined matter within dynamical quasiparticle description

A simple quasiparticle model, motivated by lowest-order perturbative QCD, is proposed. It is applied to interpret the lattice QCD equation of state. A reasonable reproduction of the lattice data is obtained. In contrast to existing quasiparticle models, the present model is formulated in dynamical rather than thermodynamical terms, and is easily applicable to a system with finite baryon density. In particular, the model simulates the confinement property.

hep-ph↗

arXiv2003

Evolution of Baryon-Free Matter Produced in Relativistic Heavy-Ion Collisions

A 3-fluid hydrodynamic model is introduced for simulating heavy-ion collisions at incident energies between few and about 200 AGeV. In addition to the two baryon-rich fluids of 2-fluid models, the new model incorporates a third, baryon-free (i.e. with zero net baryonic charge) fluid which is created in the mid-rapidity region. Its evolution is delayed due to a formation time $τ$, during which the baryon-free fluid neither thermalizes nor interacts with the baryon-rich fluids. After formation it thermalizes and starts to interact with the baryon-rich fluids. It is found that for $τ$=0 the interaction strongly affects the baryon-free fluid. However, at reasonable finite formation time, $τ$=1 fm/c, the effect of this interaction turns out to be substantially reduced although still noticeable. Baryonic observables are only slightly affected by the interaction with the baryon-free fluid.

nucl-th↗

arXiv2003

Three-Fluid Simulations of Relativistic Heavy-Ion Collisions

A relativistic 3-fluid 3D hydrodynamic model has been developed for describing heavy-ion collisions at incident energies between few and $\sim$ 200 A$\cdot$GeV. In addition to two baryon-rich fluids which simulate mutually decelerating counterflows of target and projectile nucleons, the new model incorporates evolution of a third, retarded baryon-free fluid created by this decelerated baryonic matter. Different equations of state, including those with the deconfinement phase transition, are treated. A reasonable agreement with experiment is illustrated by proton rapidity spectra, their dependence on collision centrality and beam energy.

nucl-th↗

arXiv2003

Self-consistent Approach to Off-Shell Transport

The properties of two forms of the gradient expanded Kadanoff--Baym equations, i.e. the Kadanoff--Baym and Botermans-Malfliet forms, suitable to describe the transport dynamics of particles and resonances with broad spectral widths, are discussed in context of conservation laws, the definition of a kinetic entropy and the possibility of numerical realization. Recent results on exact conservations of charge and energy-momentum within Kadanoff-Baym form of quantum kinetics based on local coupling schemes are extended to two cases relevant in many applications. These concern the interaction via a finite range potential, and, relevant in nuclear and hadron physics, e.g. for the pion--nucleon interaction, the case of derivative coupling.

nucl-th↗

arXiv2001

Exact Conservation Laws of the Gradient Expanded Kadanoff-Baym Equations

It is shown that the Kadanoff-Baym equations at consistent first-order gradient approximation reveal exact rather than approximate conservation laws related to global symmetries of the system. The conserved currents and energy-momentum tensor coincide with corresponding Noether quantities in the local approximation. These exact conservations are valid, provided a Phi-derivable approximation is used to describe the system, and possible memory effects in the collision term are also consistently evaluated up to first-order gradients.

nucl-th↗

arXiv2000

Directed Flow of Baryons in Heavy-Ion Collisions

The collective motion of nucleons from high-energy heavy-ion collisions is analyzed within a relativistic two-fluid model for different equations of state (EoS). As function of beam energy the theoretical slope parameter F_y of the differential directed flow is in good agreement with experimental data, when calculated for the QCD-consistent EoS described by the statistical mixed-phase model. Within this model, which takes the deconfinement phase transition into account, the excitation function of the directed flow turns out to be a smooth function in the whole range from SIS till SPS energies. This function is close to that for pure hadronic EoS and exhibits no minimum predicted earlier for a two-phase bag-model EoS. Attention is also called to a possible formation of nucleon antiflow (F_y < 0) at energies of the order of 100 A GeV.

nucl-th↗

arXiv2000

Soft Modes, Resonances and Quantum Transport

Effects of the propagation of particles, which have a finite life-time and an according width in their mass spectrum, are discussed in the context of transport description. First, the importance of coherence effects (Landau-Pomeranchuk-Migdal effect) on production and absorption of field quanta in non-equilibrium dense matter is considered. It is shown that classical diffusion and Langevin results correspond to re-summation of certain field-theory diagrams formulated in terms of full non-equilibrium Green's functions. Then the general properties of broad resonances in dense and hot systems are discussed in the framework of a self-consistent and conserving Phi-derivable method of Baym at the examples of the rho-meson in hadronic matter and the pion in dilute nuclear matter. Further we address the problem of a transport description that properly accounts for the damping width of the particles. The Phi-derivable method generalized to the real-time contour provides a self-consistent and conserving kinetic scheme. We derive a generalized expression for the non-equilibrium kinetic entropy flow, which includes corrections from fluctuations and mass-width effects. In special cases an H-theorem is proved. Memory effects in collision terms give contributions to the kinetic entropy flow that in the Fermi-liquid case recover the famous bosonic type T^3 ln T correction to the specific heat of liquid Helium-3. At the example of the pion-condensate phase transition in dense nuclear matter we demonstrate important part played by the width effects within the quantum transport.

nucl-th↗

arXiv2000

Soft Modes, Quantum Transport and Kinetic Entropy

The effects of the propagation of particles which have a finite life-time and an according width in their mass spectrum are discussed in the context of transport descriptions. In the first part the coupling of soft photon modes to a source of charged particles is studied in a classical model which can be solved completely in analytical terms. The solution corresponds to a re-summation of certain field theory diagrams. The general properties of broad resonances in dense finite temperature systems are discussed at the example of the $ρ$-meson in hadronic matter. The second part addresses the problem of transport descriptions which also account for the damping width of the particles. The Kadanoff--Baym equation after gradient approximation together with the $Φ$-derivable method of Baym provides a self-consistent and conserving scheme. Memory effects appearing in collision term diagrams of higher order are discussed. We derive a generalized expression for the nonequilibrium kinetic entropy flow, which includes corrections from fluctuations and mass-width effects. In special cases an $H$-theorem is proved. Memory effects in collision terms provide contributions to the kinetic entropy flow that in the Fermi-liquid case recover the famous bosonic type $T^3 \ln T$ correction to the specific heat of liquid Helium-3.

nucl-th↗

arXiv1999

Resonance Transport and Kinetic Entropy

Within the real-time formulation of nonequilibrium field theory, generalized transport equations are derived avoiding the standard quasiparticle approximation. They permit to include unstable particles into the transport scheme. In order to achieve a self-consistent, conserving and thermodynamically consistent description, we generalize the Baym's $Φ$-functional method to genuine nonequilibrium processes. The developed transport description naturally includes all those quantum features already inherent in the corresponding equilibrium limit. Memory effects appearing in collision term diagrams of higher order are discussed. The variational properties of $Φ$-functional permit to derive a generalized expression for the non-equilibrium kinetic entropy flow, which includes fluctuations and mass width effects. In special cases an $H$-theorem is demonstrated implying that the entropy can only increase with time. Memory effects in the kinetic terms provide corrections to the kinetic entropy flow that in equilibrium limit recover the famous bosonic type $T^3 \ln T$ correction to the specific heat of Fermi liquids like Helium-3.

nucl-th↗