1,721,039 research outputs found
Strangeness instabilities in relativistic heavy-ion collisions
Full text linkIn this investigation we are going to show that, similarly to the low density nuclear liquid-gas phase transition, thermodynamic instabilities and, consequently, a pure hadronic phase transition can occur in regime of high temperature and dense baryon matter. The analysis is performed by means of an effective relativistic mean-field model with the inclusion of hyperons, Δ-isobars, and the lightest pseudoscalar and vector meson degrees of freedom. The Gibbs conditions on the global conservation of baryon number and zero net strangeness in symmetric nuclear matter are required.
It turns out that a continuous phase transition takes place with two phases at the same baryon and strangeness chemical potentials but with a different content of baryon and strangeness density, altering significantly the baryon-antibaryon and meson-antimeson ratios. Such a physical regime could be in principle investigated in the high-energy compressed nuclear matter experiments where it is possible to create compressed baryonic matter with a high net baryon density
Hadron-quark crossover phase transition in hybrid compact stars
Full text linkLattice simulation of QCD at small net baryon densities and high temperature have revealed that the transition from the hadronic phase to the deconfined quark-gluon plasma is a crossover. Recently, the structure of neutron stars have been studied with a crossover equation of state by means of a switching function to model a smooth transition from a pure neutron matter to massless quarks. The switch function parameter was constrained in order to reproduce neutron stars up to about two solar masses, with the constraint that the adiabatic sound velocity cannot exceed the speed of light. Following the same line, such a study has been extended by considering the relevance of color superconducting massless quarks in the cold dense matter. In this contribution, we investigate the crossover phase transition into hybrid compact stars by means of an equation of state which incorporates hadronic matter, composed by nucleons, hyperons and Δ-isobars degrees of freedom, massive quark matter with the inclusion of non-perturbative effects and leptons in β-stable equilibrium
Strangeness thermodynamic instabilities in hot and dense nuclear matter
Full text linkWe explore the presence of thermodynamic instabilities and, consequently, the realization of a pure hadronic phase transition in the hot and finite baryon density nuclear matter. The analysis is performed by means of an effective relativistic mean-field model with the inclusion of hyperons, Δ-isobars, and the lightest pseudoscalar and vector meson degrees of freedom. The Gibbs conditions on the global conservation of baryon number and zero net strangeness in symmetric nuclear matter are required. Similarly to the liquid–gas phase transition, we show that a phase transition, characterized by mechanical instabilities (due to fluctuations on the baryon number) and chemical-diffusive instabilities (due to fluctuations on the strangeness number), can take place for a finite range of Δ-meson coupling constants, compatible with different experimental constraints. The hadronic phase transition, which presents similar features to the quark-hadron phase transition, is characterized by different strangeness content during the mixed phase and, consequently, by a sensible variation of the strange anti-particle to particle ratios
Nuclear phase transition and thermodynamic instabilities in dense nuclear matter
Full text linkWe study the presence of thermodynamic instabilities in a nuclear medium at finite temperature and density where nuclear phase transitions can take place. Such a phase transition is characterized by pure hadronic matter with both mechanical instability (fluctuations on the baryon density) that by chemical-diffusive instability (fluctuations on the electric charge concentration). Similarly to the liquid-gas phase transition, the nucleonic and the Δ-matter phase have a different isospin density in the mixed phase. In the liquid-gas phase transition, the process of producing a larger neutron excess in the gas phase is referred to as isospin fractionation. A similar effects can occur in the nucleon-Δ matter phase transition due essentially to a Δ- excess in the Δ-matter phase in asymmetric nuclear matter. In this context we also discuss the relevance of Δ-isobar and hyperon degrees of freedom in the bulk properties of the protoneutron stars at fixed entropy per baryon, in the presence and in the absence of trapped neutrinos
Thermal Fluctuations of Matter Composition and Quark Nucleation in Compact Stars
Full text linkAt the extreme densities reached in the core of neutron stars, it is possible that deconfined quark matter is produced. The formation of this new phase of strongly interacting matter is likely to occur via a first-order phase transition for the typical temperatures reached in astrophysical processes. The first seeds of quark matter would then form through a process of nucleation within the metastable hadronic phase. Here, we address the role of the thermal fluctuations in the hadronic composition on the nucleation of two-flavor quark matter. At finite temperature, the thermodynamic quantities in a system fluctuate around average values. Nucleation being a local process, it is possible that it occurs in a subsystem whose composition makes the nucleation easier. We will consider the total probability of the nucleation as the product between the probability that a subsystem has a certain hadronic composition different from the average in the bulk, and the nucleation probability in that subsystem. We will show how those fluctuations of the hadronic composition can increase the efficiency of nucleation already for temperatures similar to(0.1-1) keV. However, for temperatures less than or similar to(1-10) MeV, the needed overpressure exceeds the maximum pressure reached in compact stars. Finally, for even larger temperatures the process of nucleation can take place, even taking into account finite-size effects
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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