Hybrid stars from a constrained equation of state

We determine, within a meta-model, the properties of the nuclear matter equation of state (EoS) that allow for a phase transition to deconfinement matter. It is shown that the properties that define the isoscalar channel are the ones that are affected, in particular, a phase transition implies much larger values of the skewness and kurtosis. The effect of multi-quark interaction channels in the description of the quark phase in hybrid stars is also studied. NS properties, such as the mass and radius of the quark core, show an interplay dependence between the 8-quark vector and the 4-quark isovector-vector interactions. We show that low mass NS, M ~ 1.4M⊙, may already contain a quark core, and satisfy all existing NS observational constraints. We discuss the strangeness content of the quark core and its influence on the speed of sound.

Exploring hot and dense QCD matter with HADES

Experiments at snn s NN = 2 − 3 3 GeV provide the lowest energy point of the global effort made by the heavy-ion community in order to map the QCD phase diagram. This correspond to the highest baryon chemical potential, 700-900 MeV according to the universal freeze-out curve, and temperatures of the fireball of 60-80 MeV. The formed matter can be characterized in terms of particle spectra, fluctuations and correlations. The dilepton spectrum is dominated by thermal emission from the medium and it is sensitive to in medium hadron properties. Strangeness production occurs below the free nucleon-nucleon threshold and it is a sensitive probe to test models of strangeness propagation in matter and its coupling to baryons. Data show a common scaling of measured yields as a function of number of participating nucleons independently on the strangeness content or mass of the hadron. Strangeness propagation in cold nuclear matter produced in pion induced reactions on heavy and light targets shows a significant absorption of negative kaons in heavy targets as well as a similar behaviour of ϕ indicating a strong coupling of ϕ with nucleons. Two-pion correlations, flow harmonics, fluctuations are explored as well in order to further pin down the properties of the created matter.

Melting and freeze-out conditions of hadrons in a thermal medium

We describe two independent frameworks which provide unambiguous determinations of the deconfinement and the decoupling conditions of a relativistic gas at finite temperature. First, we use the Polyakov-Nambu-Jona–Lasinio model to compute meson and baryon masses at finite temperature and determine their melting temperature as a function of their strangeness content. Second, we analyze a simple expanding gas within a Friedmann-Robertson-Walker metric, which admits a well-defined decoupling mechanism. We examine the decoupling time as a function of the particle mass and cross section. We find evidences of an inherent dependence of the hadronization and freeze-out conditions on flavor, and on mass and cross section, respectively.

Thermodynamic instabilities in high energy heavy-ion collisions

One of the very interesting aspects of high energy heavy-ion collisions experiments is a detailed study of the thermodynamical properties of strongly interacting nuclear matter away from the nuclear ground state. In this direction, many efforts were focused on searching for possible phase transitions in such collisions. We investigate thermodynamic instabilities in a hot and dense nuclear medium where a phase transition from nucleonic matter to resonance-dominated [Formula: see text]-matter can take place. Such a phase transition can be characterized by both mechanical instability (fluctuations on the baryon density) and by chemical-diffusive instability (fluctuations on the strangeness concentration) in asymmetric nuclear matter. In analogy with the liquid–gas nuclear phase transition, hadronic phases with different values of antibaryon–baryon ratios and strangeness content may coexist. Such a physical regime could be, in principle, investigated in the future high-energy compressed nuclear matter experiments which will make it possible to create compressed baryonic matter with a high net baryon density.