118 research outputs found
Helicity and vorticity in heavy-ion collisions at NICA energies
Heavy-ion collisions at center-of-mass nucleon collision energies 4.5--11.5
GeV are analyzed within the PHSD transport model. Spectator nucleons are
separated, and the transfer of the initial angular momentum of colliding nuclei
to the fireball formed by participants is studied. The maximal angular momentum
is carried by the fireball in gold-gold collisions with the impact parameter
about 5 fm corresponding to centrality class 10--20\%. The obtained participant
distributions were fluidized and the energy and baryon number densities,
temperature, and velocity fields are obtained in the Landau frame. It is shown
that the velocity field has dominantly Hubble-like transversal and longitudinal
expansion with the vortical motion being only a small correction on top of it.
The vorticity field is calculated and illustrated in detail. The formation of
two oppositely-rotating vortex rings moving in opposite directions along the
axis is demonstrated. Other characteristics of the vortical motion such as
the Lamb vector field and the kinematic vorticity number are considered. The
magnitude of the latter one is found to be smaller than that for the Poiseuille
flow and close to the pure shear deformation corresponding to just a flattening
of fluid cells. The field of hydrodynamic helicity, which is responsible for
the axial vortex effect, is calculated. The separation of positive and negative
helicities localized upper and lower semi-planes with respect to the reaction
plane is shown. It is proved that the areas with various helicity signs can be
probed by the selection of hyperons with positive and negative
projections of their momenta orthogonal to the reaction plane.Comment: 22 pages, 23 figures. Figure labels are corrected, references adde
Catalytic Reactions in Heavy-ion Collisions
We discuss a new type of reactions of a phi meson production on hyperons, pi
Y--> phi Y and anti-kaons bar-K N --> phi Y. These reactions are not suppressed
according to Okubo-Zweig-Iizuka rule and can be a new efficient source of phi
mesons in a nucleus-nucleus collision. We discuss how these reactions can
affect the centrality dependence and the rapidity distributions of the phi
yield.Comment: talk at 6th International Workshop on Critical Point and Onset of
Deconfinment (CPOD2010), Dubna, August 22-28, 201
Phi Mesons from a Hadronic Fireball
Production of mesons is considered in the course of heavy-ion
collisions at SPS energies. We investigate the possible difference in momentum
distributions of mesons measured via their leptonic () and
hadronic () decays. Rescattering of secondary kaons in the dense hadron
gas together with the influence of in-medium kaon potential can lead to a
relative decrease of a yield observed in the hadronic channel. We
analyze how the in-medium modifications of meson properties affect apparent -
reconstructed momentum distributions of mesons. Quantitative results are
presented for central Pb+Pb collisions at .Comment: style Revtex4,9 pages, 5 figures. submitted to Phys. Rev.
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.Comment: 13 p., 8 figs., 7 tables, Version accepted by Phys. Rev.
Neutral weak currents in nucleon superfluid Fermi liquids: Larkin-Migdal and Leggett approaches
Neutrino emission in processes of breaking and formation of nucleon Cooper
pairs is calculated in the framework of the Larkin-Migdal and the Leggett
approaches to the description of superfluid Fermi liquids at finite
temperatures. We explain peculiarities of both approaches and explicitly
demonstrate that they lead to the same expression for the emissivity in pair
breaking and formation processes.Comment: 24 pages, 3 figure
Contribution of the massive photon decay channel to neutrino cooling of neutron stars
We consider massive photon decay reactions via intermediate states of
electron-electron-holes and proton-proton-holes into neutrino-antineutrino
pairs in the course of neutron star cooling. These reactions may become
operative in hot neutron stars in the region of proton pairing where the photon
due to the Higgs-Meissner effect acquires an effective mass that
is small compared to the corresponding plasma frequency. The contribution of
these reactions to neutrino emissivity is calculated; it varies with the
temperature and the photon mass as
for . Estimates show that these processes appear as extra
efficient cooling channels of neutron stars at temperatures K.Comment: accepted to publication in Zh. Eksp. Teor. Fiz. (JETP
Negative Kaons in Dense Baryonic Matter
Kaon polarization operator in dense baryonic matter of arbitrary isotopic
composition is calculated including s- and p-wave kaon-baryon interactions. The
regular part of the polarization operator is extracted from the realistic
kaon-nucleon interaction based on the chiral and 1/N_c expansion. Contributions
of the Lambda(1116), Sigma(1195), Sigma*(1385) resonances are taken explicitly
into account in the pole and regular terms with inclusion of mean-field
potentials. The baryon-baryon correlations are incorporated and fluctuation
contributions are estimated. Results are applied for K- in neutron star matter.
Within our model a second-order phase transition to the s-wave K- condensate
state occurs at rho_c \gsim 4 \rho_0 once the baryon-baryon correlations are
included. We show that the second-order phase transition to the p-wave
condensate state may occur at densities in
dependence on the parameter choice. We demonstrate that a first-order phase
transition to a proton-enriched (approximately isospin-symmetric) nucleon
matter with a p-wave K- condensate can occur at smaller densities, \rho\lsim 2
\rho_0. The transition is accompanied by the suppression of hyperon
concentrations.Comment: 41 pages, 24 figures, revtex4 styl
Isospin Effects on Strangeness in Heavy-Ion Collisions
Kaon properties are studied within the framework of a fully covariant
transport approach. The kaon-nucleon potential is evaluated in two schemes, a
chiral perturbative approach and an effective One-Boson-Exchange model. Isospin
effects are explicitly accounted for in both models. The transport calculations
indicate a significant sensitivity of momentum distributions and total yields
of isospin states on the choice of the kaon-nucleon interaction.
Furthermore, isospin effects are rather moderate on absolute kaon yields, but
appear on strangeness ratios. This is an important issue in determining the
high density symmetry energy from studies of strangeness production in
heavy-ion collisions.Comment: 15 papes, 5 figures. Accepted for publication in Nuclear Physic
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