Phase Transition In Hadronic Matter Research Articles

Hybrid stars in a relativistic quark model

The phase transition of hadronic matter to deconfined quark matter in the interior of the neutron star is studied. A relativistic quark model is used to describe the hadronic matter whereas the MIT bag model is used to represent the quark matter. The coexistence of hadron-quark mixed phase in equilibrium is also investigated. The equation of state with nucleon $+$ quark (NP-hybrid) and nucleon $+$ hyperon $+$ quark (NP $+$ hyp-hybrid) matter is developed and stellar properties, such as the maximum mass, radii, tidal deformability, and gravitational redshift are determined. The behavior of the speed of sound and the adiabatic index in the hybrid matter are also studied. It is found that within the conformal limits of the speed of sound, stars below the $2\text{\ensuremath{-}}{M}_{\ensuremath{\bigodot}}$ limit lack a sizable quark core but exhibit mixed phase of hadrons and quarks.

THE ROLE OF ANTIKAON CONDENSATES IN THE ISOSPIN ASYMMETRY OF NEUTRON STARS

We study the effects of the scalar-isovector light mesons on the isospin asymmetry and phase transition of hadronic matter to hadronic matter with a condensate of antikaons, using an effective model with derivative couplings. In our formalism, nucleons interact through the exchange of σ, ω, ϱ, δ, and ς mesons in the presence of electrons and muons to accomplish electric charge neutrality and beta equilibrium. The phase transition to the antikaons condensate was implemented through the Gibbs conditions combined with the mean-field approximation, giving rise to a mixed phase of coexistence between nucleon matter and the condensed antikaons. As expected, our results indicate that the scalar-isovector mesons increase the range of the mixed phase–space, they operate for restoring isospin symmetry and they reduce the value of the effective nucleon mass, independently of the depth of the optical potential for antikaons. Also as expected the increase of the depth of optical potential favors the population of antikaons. Our results predict the density threshold of birth of the K-antikaons. The most expressive result of our calculation is the abrupt change in the isospin asymmetry due to the presence of the condensate. Moreover, we have found that scalar-isovector mesons increase the fraction of protons and reduced the fraction of neutrons in the system, since these mesons couple with the conserved isovector current of baryons and thus the minimum in the energy of the system corresponds to saturated isospin states (symmetric in isospin). Finally, we have found as expected that these mesons produce the stiffness of the EoS.

THE ROLE OF SCALAR-ISOVECTOR MESONS AND ANTIKAONS IN NEUTRON STARS

We study the effects of the scalar-isovector meson δ and those of a new light scalar-isovector resonance ς on the phase transition of hadronic matter to hadronic matter with a condensate of antikaons, using an effective model with derivative couplings. In our formalism, nucleons interact through the exchange of σ, ω, ϱ, δ, and ς mesons in the presence of electrons and muons to accomplish electric charge neutrality and beta equilibrium. The phase-transition to the antikaon condensate was implemented through the Gibbs conditions combined with the mean-field approximation, giving rise to a mixed phase of coexistence between nucleon matter and the condensed antikaons. Scalar-isovector mesons operate for restoring isospin symmetry and reduce this way the value of the effective nucleon mass, independent of the depth of the optical potential for antikaons. Moreover, as expected we found that an increase of the depth of optical potential favors the population of antikaons. Finally, assuming neutrino-free matter, we observe a rapid decrease of the electron chemical potential produced by the gradual substitution of electrons by kaons to accomplish electric charge neutrality.

HYBRID STARS WITH DELTA MATTER AND COLOR–FLAVOR LOCKED QUARK PHASE

The color–flavor locked (CFL) phase is believed to be the fundamental state of strange quark matter (SQM) at high densities. The CFL phase is a color superconductor composed of pairs of u, d and s quarks, with no electrons, forming a Bose condensate. In this work, we analyze a possible phase transition of hadronic matter made of nucleons, Δ–resonances, hyperons and leptons, to CFL superconducting quark matter. An equation of state taking into account this phase transition is employed to determine the characteristics of a hybrid star. The role of the color superconducting gap on the hybrid stars properties is also discussed.

The pion velocity in dense skyrmion matter

We have developed a field theory formalism to calculate in-medium properties of hadrons within a unified approach that exploits a single Lagrangian to describe simultaneously both matter background and meson fluctuations. In this paper we discuss the consequences on physical observables of a possible phase transition of hadronic matter taking place in the chiral limit. We pay special attention to the pion velocity v π , which controls, through a dispersion relation, the pion propagation in the hadronic medium. The v π is defined in terms of parameters related to the matrix element in matter of the axial-vector current, namely, the in-medium pion decay constants, f t and f s . Both of the pion decay constants change dramatically with density and even vanish in the chiral limit when chiral symmetry is restored, but the pion velocity does not go to zero, decreasing at most 10% over the whole density range studied. A possible pseudogap structure is indicated.

On the chiral phase transition in hadronic matter

A qualitative analysis of the chiral phase transition in QCD with two massless quarks and non--zero baryon density is performed. It is assumed that at zero baryonic density, \rho=0, the temperature phase transition is of the second order. Due to a specific power dependence of baryon masses on the chiral condensate the phase transition becomes of the first order at the temperature T=T_{ph}(\rho) for \rho>0. At temperatures T_{cont}(\rho) > T > T_{ph}(\rho) there is a mixed phase consisting of the quark phase (stable) and the hadron phase (unstable). At the temperature T = T_{cont}(\rho) the system experiences a continuous transition to the pure chirally symmetric phase.

Detectors and techniques in relativistic heavy ion physics

In collisions of heavy ions at relativistic energies highly excited nuclear matter is produced. Hadronic and electromagnetic probes are investigated in order to study the composition and the thermodynamical properties of the short-liver interaction volume and its expansion characteristics. The ultimate goal is to identify signals for a phase transition of hadronic matter to the quark-gluon plasma state. Because of the high multiplicity of particles in the final state various experimental techniques and analysis methods have been development in order to study exclusive signals with electromagnetic and hadronic probes. A selection of detector concepts which have been applied in heavy ion reactions at the CERN SPS will be presented here.

Double phase transition in hadronic matter at zero temperature

The phase transition at zero temperature between hadronic matter and quark-gluon plasma (QGP) is considered within bag model ideology with intermediate phase Q of deconfined constituent quarks (valons) taken into account. Nucleon interactions are treated within Mean Field Approximation method with several model interaction potentials. It is shown that for reasonable choice of model parameters intermediate Q phase appears at zero temperature as well.

A convolution formula for a phase transition of hadronic matter and the multiplicity distributions

We propose a general form for the statistical bootstrap equation by means of a convolution formula for the thermodynamical system of hadronic matter. In connection with a phase transition of hadronic matter to a state of quark liberation, we predict the negative binomial distribution with k∼1 for the multiplicity distributions in the central pseudorapidity region at high energies.

Bare-bones model for phase transition in hadronic matter

By using only an ideal gas form for both the hadronic matter and the quark-gluon plasma, together with a bag constant parametrization for the confinement effects, we construct a two-phase description of strongly interacting matter. The temperature dependences of the critical baryon number density and energy density are calculated.