Bogolyubov Institute for Theoretical Physics
of the National Academy of Sciences of Ukraine

Department of High-Density Energy Physics
  • Description of quantum liquids (Landau-Fermi liquids) resulting from the quark models with a four-fermion interaction has been given. This consideration is based on using a dressing Bogolyubov transformation and mean field approximation. It is demonstrated that the mean energy of the ensemble serves as energy functional of the Landau theory and is shown that in a wide range of potentials interesting for applications one can expect the quantum liquids to behave in essentially the same way. For some of their properties a band of estimates has been obtained. A comparison of Nambu-Jona-Lasinio and Keldysh models, substantially different in many aspects, demonstrates that the properties of quantum liquids do not actually depend on the shape of the form factor (a natural interaction length); rather, they are mainly determined by the coupling constant of the interaction. It is found out that a common distinctive feature of ensembles is the presence of degenerate states with respect to the vacuum in the chemical potential and pressure.
    G.M. Zinovjev
  • The van der Waals (VDW) equation of state predicts the existence of a first-order liquid-gas phase transition and contains a critical point. The VDW equation with Fermi statistics is applied to a description of the nuclear matter. The nucleon number fluctuations near the critical point of nuclear matter are studied. The scaled variance, skewness, and kurtosis diverge at the critical point. It is found that the crossover region of the phase diagram is characterized by the large values of the scaled variance, almost zero skewness, and by the significantly negative kurtosis. The rich structures of the skewness and kurtosis are observed in the phase diagram in the wide region around the critical point, namely, they both may attain large positive or negative values.
    D.V. Anchishkin, M.I. Gorenstein
  • From the analysis of more experimental hadronic multiplicities, than there were used before, we found at chemical freeze-out two peaks of the dimensionless measure of interaction at the center of mass collision-energies 4,9 GеV/nucl and 9,2 GеV/nucl. The strong model arguments that these two peaks provide evidence of two phase transformations at these collision energies are given. The higher peak at the collision energy 4,9 GеV/nucl gives evidence of the first order phase transition, while the smaller peak at higher energy of collision is related either to a second order phase transition or a weak cross-over.
    K.A. Bugaev, V.V. Sagun, A.I. Ivanytskyi, G.M. Zinovjev
  • The integrated hydrokinetic model of nucleus-nucleus collisions has been developed and successfully applied for description and predictions of the experimental data. The model includes the generation of the initial state of matter formed in these collisions, its thermalization and subsequent viscous hydrodynamic evolution, decay into separated hadrons, and the final stage - the evolution of non-equilibrium gas of interacting hadrons and resonances.
    V.Yu. Naboka, Yu.M. Sinyukov
  • By studying quark ensembles with infinite correlation length we formulate the quantum field theory model that, as we show, is exactly integrable and develops an instability of its standard vacuum ensemble (the Dirac sea). We argue such an instability is rooted in high ground state degeneracy (for 'realistic' space-time dimensions) featuring a fairly specific form of energy distribution, and with thecutoff parameter going to infinity this inherent energy distribution becomes infinitely narrow and leads to large (unlimited) fluctuations.
    G.M. Zinovjev
  • It is found that the phenomenological hydrodynamic approximation of relativistic nucleus-nucleus collisions can be represented as the effective theory for slow and long wave-length modes of isolated quantum systems formed at the collisions. Within this approach the evolution of energy-momentum tensor for long wave-length subsystem is analysed in scalar field theory, and it is found that the tensor approaches to the energy-momentum tensor of effective viscous liquid.
    S.V. Akkelin, Yu.M. Sinyukov
  • The elastic proton scattering data for energies from 19 GeV up to 7 TeV (TOTEM experiment at LHC) have been analyzed. "Experimental" data and errors for elastic scattering amplitude in the impact-parameter representation are extracted from the data on differential cross section. The new effect has been found. At the LHC energy the impact amplitude for the first time exceeded the black disk limit. This result, if confirmed at higher energies, will have important consequences for many existing models as well as for an actual understanding the high energy dynamics of hadron elastic scattering.
    E.S. Martynov, A.O. Alkin
  • Using the through analysis of experimental hadronic multiplicities measured in the central nuclear collisions, at chemical freeze-out we found the novel peculiar irregularities of various thermodynamic quantities at the center of mass collision energies4,3-4,9 GеV/nucl. The most remarkable irregularities are an unprecedented jump of the number of effective degrees of freedom observed in this narrow energy range and the plateaus in the collision-energy dependence of the entropy per baryon, total pion number per baryon, and thermal pion number per baryon at laboratory energies 6.9-11.6 AGeV. Within the compression shock-adiabat model we demonstrate that these irregularities are caused by a formation of the quark-gluon-hadron mixed phase in nucleus-nucleus collisions.
    K.A. Bugaev, O.I. Ivanytskyi
  • The strongly intensive measures are used to calculate effects appeared due to decays of hadronic resonances for particle number fluctuations of positively and negatively charged pions. Both analytical and computer numerical calculations have been done for nucleus-nucleus collisions in the statistical hadron-resonance gas model and in the relativistic transport UrQMD model.
    M.I. Gorenstein
  • The phenomenological model of confinement which treats the color string as a cylindrical bag with a surface tension is proposed. It provides with the relation between the surface tension of quark-gluon bags and color string tension and allows to determine the bag surface tension directly from lattice QCD calculations.
    K.A. Bugaev, G.M. Zinovjev
  • New equation of state for a quark-gluon plasma is proposed. It obeys the specific qualitative features discovered in the lattice QCD calculations and gives the good agreement with the results of lattice SU(3) gluodynamics simulations.
    V.V. Begun, M.I. Gorenstein, O.A. Mogilevsky
  • The model of non-femtoscopic correlations in proton-proton collisions is developed. This model absorbs the correlations induced by the conservation laws and also the correlations induced by the microjets. It successfully describes non-femtoscopic correlation functions of identical pions which have been received by analyzing the proton-proton collision data at the LHC energy 900 GeV.
    S.V. Akkelin, Yu.M. Sinyukov