Zhu Ming-Feng

Effects of δ Meson on Thermal Protoneutron Star Matter

In the framework of the relativistic mean field theory, the effects of the δ meson on protoneutron star matter with hyperons at unite temperature are investigated. In thermal protoneutron star matter, the δ field potential increases with density first and then decreases. Fixing the density, the increase of the temperature suppresses the S field potential. With the inclusion of the δ meson, the threshold densities for hyperons become lower and the abundance of trapped neutrinos decreases. The most important effect of the δ meson is to increase the abundance of hyperons in the inner core range of protoneutron stars. With the rise of the temperature, the density range where the δ meson plays an important role is narrowed and the effects of the δ meson are suppressed. Moreover, the protoneutron star mass and radius are nearly not affected by the δ meson.

Direct Urca Processes with Hyperons in Cooling Neutron Stars

In the relativistic mean field approximation, the relativistic energy losses of the direct Urca processes with nucleons (N-DURCA) and hyperons (Y-DURCA) are studied in the degenerate baryon matter of neutron stars. We investigate the effects of hyperon degrees of freedom and the Y-DURCA processes on the N-DURCA processes, and the total neutrino emissivity of neutron star matter. The results show that the existence of hyperons decreases the abundance of protons and leptons, and can sharply suppress the neutrino emissivity of the N-DURCA processes.

1S0 Nucleon Superfluidity in Neutron Star Matter

We investigate the nucleon superfluidity in the 1S0 channel in neutron star matter using the relativistic mean field theory and the BCS theory. We discuss particularly the influence of the isovector scalar interaction which is considered by exchanging δ meson on the nucleon superfluidity. It is found that the δ meson leads to a growth of the nucleon 1S0 pairing energy gaps in a middle density range of the existing nucleon superfluidity. In addition, when the density ρB > 0.36 fm−3, the proton 1S0 pairing energy gap obviously decreases. The density range of the proton 1S0 superfluidity is narrowed due to the presence of δ mesons. In our results, the δ meson not only changes the EOS and bulk properties but also changes the cooling properties of neutron stars.

The Effects of δ Meson on the Neutron Star Cooling

In the framework of the relativistic mean field theory, the isovector scalar interaction is considered by exchanging δ meson to study the influence of δ meson on the cooling properties of neutron star matter. The calculation results show that with the inclusion of δ meson, the neutrino emissivity of the direct Urca processes increases, and thus enhances the cooling of neutron star matter. When strong proton superfluidity is considered, the theoretical cooling curves agree with the observed thermal radiation for isolated neutron stars.

Thermal protoneutron stars with hyperons

The properties of thermal protoneutron star matter including hyperons are investigated in the framework of the relativistic mean field theory (RMFT). In protoneuron star matter, with the increase of the temperature, the critical densities of hyperons decrease, the sequence for appearances of hyperons change, the abundances of hyperons as well as neutrinos increase, and the strong interactions between baryons get weaker. Meanwhile, the abundances of isospin multiple states for nucleons, Σ, and Ξ become identical, leading to isospin saturated symmetric matter, respectively. Moreover, if a protoneutron star is born with higher temperature, it is less likely to convert to a black hole.

K̄0 Condensation in Hyperonic Neutron Star Matter

In the framework of the relativistic mean field theory, we investigate K0 condensation along with K− condensation in neutron star matter including the baryon octet. The results show that both K0 and K− condensations can occur well in the core of the maximum mass stars for relatively shallow optical potentials of K in the range of −10MeV ~ −160 MeV. With the increasing optical potential of K, the critical densities of K decrease and the species of baryons appearing in neutron stars become fewer. The main role of K0 condensation is to make the abundances of particles become identical leading to isospin saturated symmetric matter including antikaons, nucleons and hyperons. K− condensation is chiefly responsible for the softening of the corresponding equation of state, which leads to a large reduction in the maximum masses of neutron stars. In the core of massive neutron stars, neutron star matter including rich particle species, such as antikaons, nucleons and hyperons, may exist.

Influence of Model Parameters on Hadron-Quark Phase Transition in Neutron Star Matter

Abstract We study the influence of the model parameters on the phase transitions, the equation of state (EOS), andthe corresponding mass-radius relations in the interior of neutron stars. The numerical analysis shows that the couplingconstants of hyperons have a slight influence on the phase transitions and EOS, but an obvious influence on the particlefractions, while the bag constant B and coupling constant g have an important influence on the phase transitions, theEOS, and the mass-radius relations. We find that both the bag constant B and coupling constant g play the same rolein the description of the interactions between quarks of hybrid stars. The maximum mass calculated by using the bagconstant determined with experimental data (ranging from 175 to 200 MeV) falls in the interval of 1.4 ∼ 1.7 solar mass.The corresponding radius is between 9.3 and 12 km. These results are in agreement with observed values of neutronstars. The possibility of the existence of a third family is discussed. The detection of a third family may provide asignature for a phase transition inside neutron stars.PACS numbers:

Bulk Properties of Hybrid Stars with the Color-Flavor Locked Quark Matter Core

We investigate the influence of the energy gap (Δ) of the color-flavor locked (CFL) quark phase on the bulk properties of hybrid stars. The relativistic mean field model is used for hadronic matter and the MIT bag model for CFL quark matter. In our calculation results, we find that with the increase of the CFL energy gap there exists a transition behavior, which goes from the hadron star range through the transition range into the CFL quark star range. The observation data of PRS J1614-2230 are in the hadron star range (with Δ < 40 MeV). We also find that with hyperons the equation of state (EOS) for the hybrid star matter with the CFL quark matter core has a small change, which can be disregarded.

bar K Condensation in Neutron Star Matter with Δ Quartet

In the framework of relativistic mean field theory, the condensations of K− and 0 in neutron star matter including baryon octet and Δ quartet are studied. We find that in this case K− and 0 condensations can occur at relative shallow optical potential depth of from −80 MeV to −160 MeV. Both K− and 0 condensations favor the appearances of Δ resonances. With condensations all the Δ quartet can appear well inside the maximum mass stars. The appearances of Δ resonances change the composition and distribution of particles at high densities. The populations of Δ resonances can enhance K− condensation. It is found that in the core of massive neutron stars, neutron star matter includes rich particle species, such as antikaons, baryon octet, and Δ quartet. In the presence of Δ resonances and condensation, the EOS becomes softer and results in smaller maximum mass stars. Furthermore the impact of antikaon condensations, hyperons, and Δ resonances on direct Urca process with nucleons is also discussed briefly.

Properties of hybrid stars in an extended MIT bag model

The properties of hybrid stars are investigated in the framework of the relativistic mean field theory (RMFT) and an MIT bag model with density-dependent bag constant to describe the hadron phase (HP) and quark phase (QP), respectively. We find that the density-dependent B(ρ) decreases with baryon density ρ; this decrement makes the strange quark matter become more energetically favorable than ever, which makes the threshold densities of the hadron-quark phase transition lower than those of the original bag constant case. In this case, the hyperon degrees of freedom can not be considered. As a result, the equations of state of a star in the mixed phase (MP) become softer whereas those in the QP become stiffer, and the radii of the star obviously decrease. This indicates that the extended MIT bag model is more suitable to describe hybrid stars with small radii.