Relativistic Nuclear Equation Of State Research Articles

Thermodynamic instabilities in dense asymmetric nuclear matter and in compact stars

We investigate the presence of thermodynamic instabilities in compressed asymmetric baryonic matter, reachable in high energy heavy ion collisions, and in the cold β-stable compact stars. To this end we study the relativistic nuclear equation of state with the inclusion of Δ-isobars and require the global conservation of baryon and electric charge numbers. Similarly to the low density nuclear liquid-gas phase transition, we show that a phase transition can occur in dense asymmetric nuclear matter and it is characterized by both mechanical instability (fluctuations on the baryon density) and by chemical-diffusive instability (fluctuations on the electric charge concentration). Such thermodynamic instabilities can imply a very different electric charge fraction Z/A in the coexisting phases during the phase transition and favoring an early formation of Δ− particles with relevant phenomenological consequences in the physics of the protoneutron stars and compact stars. Finally, we discuss the possible co-existence of very compact and very massive compact stars in terms of two separate families: compact hadronic stars and very massive quark stars.

Nonextensive statistical effects and strangeness production in hot and dense nuclear matter

By means of an effective relativistic nuclear equation of state in the framework of the nonextensive statistical mechanics, characterized by power-law quantum distributions, we study the phase transition from hadronic matter to quark–gluon plasma at finite temperature and baryon density. The analysis is performed by requiring the Gibbs conditions on the global conservation of baryon number, electric charge fraction and zero net strangeness. We show that nonextensive statistical effects strongly influence the strangeness production during the pure hadronic phase and the hadron–quark–gluon mixed phase transition, also for small deviations from the standard Boltzmann–Gibbs statistics.

Non-Gaussian statistics and the relativistic nuclear equation of state

We investigate possible effects of quantum power-law statistical mechanics on the relativistic nuclear equation of state in the context of the Walecka quantum hadrodynamics theory. By considering the Kaniadakis non-Gaussian statistics, characterized by the index κ (Boltzmann–Gibbs entropy is recovered in the limit κ → 0 ), we show that the scalar and vector meson fields become more intense due to the non-Gaussian statistical effects ( κ ≠ 0 ). From a analytical treatment, an upper bound on κ ( κ < 1 / 4 ) is found. We also show that as the parameter κ increases the nucleon effective mass diminishes and the equation of state becomes stiffer. A possible connection between phase transitions in nuclear matter and the κ-parameter is largely discussed.

Nonextensive effects on the relativistic nuclear equation of state

As widely known, the Walecka many-body field theory plays an important role in nuclear physics. This paper investigates such a theory in the context of quantum nonextensive statistical mechanics, characterized by a dimensionless parameter $q$. To this end, we consider nuclear matter described statistically by a power-law distribution which generalizes the standard Fermi-Dirac distribution ($q=1$). We show that the scalar and vector meson fields become more intense because of the nonextensive effects ($q\ensuremath{\ne}1$). From a numerical treatment, we also show that as the nonextensive parameter $q$ increases, the nucleon effective mass diminishes and the equation of state becomes stiffer. Finally, the usual Maxwell construction seems not to be necessary for isotherms with temperatures in the range $14l{k}_{B}Tl20$ MeV.

Nonlinear dynamics and statistical effects on the relativistic nuclear equation of state

On the basis of the Tsallis' nonextensive thermostatistics, we study a generalized relativistic thermodynamics and the equation of state for an ideal gas. These results are extended to derive the relativistic nuclear equation of state in the hadronic and in the quark-gluon plasma phase. We show that small deviations from the standard extensive statistics, due to long-range and memory interactions between particles inside the non-ideal plasma at high temperature and density, imply remarkable effects in the shape of the nuclear equation of state.

Nonextensive statistical effects on the relativistic nuclear equation of state

Following the basic prescriptions of the Tsallis’ nonextensive thermodynamics, we study the relativistic nonextensive thermodynamics and the equation of state for a perfect gas at the equilibrium. The obtained results are used to study the relativistic nuclear equation of state in the hadronic and in the quark–gluon plasma phase. We show that small deviations from the standard extensive statistics imply remarkable effects into the shape of the equation of state.

Nuclear equation of state at high density and the properties of neutron stars

We discuss the relativistic nuclear equation of state (EOS) using a relativistic transport model in heavy-ion collisions. From the baryon flow for $Au + Au$ systems at SIS to AGS energies and above we find that the strength of the vector potential has to be reduced moderately at high density or at high relative momenta to describe the flow data at 1-10 A GeV. We use the same dynamical model to calculate the nuclear EOS and then employ this to calculate the gross structure of the neutron star considering the core to be composed of neutrons with an admixture of protons, electrons, muons, sigmas and lambdas at zero temperature. We then discuss these gross properties of neutron stars such as maximum mass and radius in contrast to the observational values.

Neutron star properties and the relativistic nuclear equation of state of many-baryon matter

A relativistic model of baryons interacting via the exchange of σ-, ω-, π- and ρ-mesons (scalar-vector-isovector (SVI) theory) is used to describe the properties of both dense and superdense matter. For the theoretical frame, we used the temperature-dependent Green's function formalism. The equation of state (EOS) is calculated for nuclear as well as neutron matter in the Hartree (H) and Hartree-Fock (HF) approximation. The existence of phase transitions has been investigated. The isotherms of pressure as a function of density show for nuclear matter a critical temperature of about T c HF = 16.6 MeV. (As in the usual scalar-vector (SV) theory, the phase transition is absent for neutron matter. A phase transition of both many-baryon systems in the high-pressure and high-density region, which has been found within the SV many-baryon theory, appears in the SVI theory too. The calculated maximum stable masses of neutron stars depend on (1) the underlying parameter set and/or (2) on the chosen approximation (i.e., H, HF; SV-, SVI theory, respectively). Hartree calculations lead to amass stability limit of M max H ⩽ 2.87 M ⊙ ( M max H ⩽ 2.44 M ⊙ when hyperons are taken into account). For the HF calculations we obtained M max HF ⩽ 3.00 M ⊙ ( M max HF ⩽2.85 M ⊙). The corresponding maximum radii are (same notation as above) R H ⩽ 13.2 km ( R H ⩽ 11.8 km), R HF ⩽ 14.0 km ( R HF 0 13.94km). The influence of the approximations, parameter sets and hyperons on the neutron star's moment of inertia is exhibited.