Hadron-quark mixed phase in neutron stars

Possibility of structured mixed phase at first order phase transitions is examined by taking into account of charge screening and surface effects. Hadron-quark phase transition in dense neutron star interiors is considered as a concrete example.Comment: Talk given at the 7th International Symposium on "Nuclei in the Cosmos", July 8-12,200

Thermodynamics of resonances and blurred particles

Exact and approximate expressions for thermodynamic characteristics of heated matter, which consists of particles with finite mass-widths, are constructed. They are expressed in terms of Fermi/Bose distributions and spectral functions, rather than in terms of more complicated combinations between real and imaginary parts of the self-energies of different particle species. Therefore thermodynamically consistent approximate treatment of systems of particles with finite mass-widths can be performed, provided spectral functions of particle species are known. Approximation of the free resonance gas at low densities is studied. Simple ansatz for the energy dependence of the spectral function is suggested that allows to fulfill thermodynamical consistency conditions. On examples it is shown that a simple description of dense systems of interacting particle species can be constructed, provided some species can be treated in the quasiparticle approximation and others as particles with widths. The interaction affects quasiparticle contributions, whereas particles with widths can be treated as free. Example is considered of a hot gas of heavy fermions strongly interacting with light bosons, both species with zero chemical potentials. The density of blurred fermions is dramatically increased for high temperatures compared to the standard Boltzmann value. The system consists of boson quasiparticles (with effective masses) interacting with fermion -- antifermion blurs. In thermodynamical values interaction terms partially compensate each other. Thereby, in case of a very strong coupling between species thermodynamical quantities of the system, like the energy, pressure and entropy, prove to be such as for the quasi-ideal gas mixture of quasi-free fermion blurs and quasi-free bosons.Comment: 35 page

Charge Screening at First Order Phase Transitions

Possibility of structured mixed phases at first order phase transitions is examined with taking into account of charge screening and surface effects. Hadron-quark phase transition in dense neutron star interior is considered, as concrete example.Comment: 15 pages, 1 figur

Hadron Liquid with a Small Baryon Chemical Potential at Finite Temperature

First, within one diagram of $\Phi$ we discuss general properties of a system of heavy fermions of one kind (including antiparticles) interacting with rather light bosons of one kind. Fermion chemical potential is assumed to be small, \mu_f \lsim T. Already for the low temperature, $T\ll {min} (T_{\rm bl.f}, m_{b})$, the fermion mass shell proves to be partially blurred due to multiple fermion rescatterings on virtual bosons, $m_{b}$ is the boson mass, $T_{\rm bl.f}$ $(\ll m_f)$ is the typical temperature corresponding to a complete blurring of the gap between fermion-antifermion continua, $m_f$ is the fermion mass. As the result, the ratio of the number of fermion-antifermion pairs to the number provided by the ordinary Boltzmann distribution becomes larger than unit ($R_N >1$). For T\gsim m_{b}^* (T) (hot hadron liquid, blurred boson continuum), $m_{b}^* (T)$ is the effective boson mass, the abundance of all particles dramatically increases. The effective fermion mass $m_f^* (T)$ decreases with the temperature increase. For T\gsim T_{\rm bl.f} fermions are essentially relativistic particles. Due to the interaction of the boson with fermion-antifermion pairs, $m_{b}^* (T)$ decreases leading to the possibility of the ``hot Bose condensation'' for $T>T_{cb}$. The phase transition might be of the second order or of the first order depending on the species under consideration. We estimate $R_N \sim 1.5$ for $T\sim m_{\pi}/2$; $T_{\rm bl.f}$ proves to be near $T_{cb}$; both values are in the vicinity of the pion mass $m_{\pi}$.Comment: 83p, 5 figure

Neutrino Cooling of Neutron Stars. Medium effects

This review demonstrates that neutrino emission from dense hadronic component in neutron stars is subject of strong modifications due to collective effects in the nuclear matter. With the most important in-medium processes incorporated in the cooling code an overall agreement with available soft X ray data can be easily achieved. With these findings so called "standard" and "non-standard" cooling scenarios are replaced by one general "nuclear medium cooling scenario" which relates slow and rapid neutron star coolings to the star masses (interior densities). In-medium effects take important part also at early hot stage of neutron star evolution decreasing the neutrino opacity for less massive and increasing for more massive neutron stars. A formalism for calculation of neutrino radiation from nuclear matter is presented that treats on equal footing one-nucleon and multiple-nucleon processes as well as reactions with resonance bosons and condensates. Cooling history of neutron stars with quark cores is also discussed.Comment: To be published in "Physics of Neutron Star Interiors", Eds. D. Blaschke, N.K. Glendenning, A. Sedrakian, Springer, Heidelberg (2001

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 $K^-$ condensate state may occur at densities $\rho_c \sim 3\div 5 \rho_0$ 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

Remarks concerning bulk viscosity of hadron matter in relaxation time ansatz

The bulk viscosity is calculated for hadron matter produced in heavy-ion collisions, being described in the relaxation time approximation withi n the relativistic mean- field-based model with scaled hadron masses and couplings. W e show how different approximations used in the literature affect the result. Nume rical evaluations of the bulk viscosity with three considered models deviate not much from each other confirming earlier results.Comment: 17 pages, 3 figure

Self-Consistent Approximations to Non-Equilibrium Many-Body Theory

Within the non-equilibrium Green's function technique on the real time contour, the Phi-functional method of Baym is reviewed and generalized to arbitrary non-equilibrium many-particle systems. The scheme may be closed at any desired order in the number of loops or vertices of the generating functional. It defines effective theories, which provide a closed set of coupled classical field and Dyson equations, which are self-consistent, conserving and thermodynamically consistent. The approach permits to include unstable particles and therefore unifies the description of resonances with all other particles, which obtain a mass width by collisions, decays or creation processes in dense matter. The inclusion of classical fields enables the treatment of soft modes and phase instabilities. The method can be taken as a starting point for adequate and consistent quantum improvements of the in-medium rates in transport theories.Comment: 31 pages, Latex elsart-styl

Constraints on the high-density nuclear equation of state from the phenomenology of compact stars and heavy-ion collisions

A new scheme for testing nuclear matter equations of state (EsoS) at high densities using constraints from neutron star phenomenology and a flow data analysis of heavy-ion collisions is suggested. An acceptable EoS shall not allow the direct Urca process to occur in neutron stars with masses below $1.5~M_{\odot}$, and also shall not contradict flow and kaon production data of heavy-ion collisions. Compact star constraints include the mass measurements of 2.1 +/- 0.2 M_sun (1 sigma level) for PSR J0751+1807, of 2.0 +/- 0.1 M_sun from the innermost stable circular orbit for 4U 1636-536, the baryon mass - gravitational mass relationships from Pulsar B in J0737-3039 and the mass-radius relationships from quasiperiodic brightness oscillations in 4U 0614+09 and from the thermal emission of RX J1856-3754. This scheme is applied to a set of relativistic EsoS constrained otherwise from nuclear matter saturation properties with the result that no EoS can satisfy all constraints simultaneously, but those with density-dependent masses and coupling constants appear most promising.Comment: 15 pages, 8 figures, 5 table

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 $\Phi$-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 $\Phi$-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.Comment: 50 pages, submitted to Nucl. Phys.