Liu Guang-Zhou

Influence of ?* and varphi Mesons on ? Hyperon 1S0 Superfluidity in Neutron Star Matter

Within the framework of the relativistic mean field theory, we investigate the 1S0 superfluidity (SF) of ? hyperons in neutron star (NS) matter including ?* and mesons. The energy gap of ? hyperons is calculated with the Nijmegen one-boson-exchange potentials for a ?? pair. The parameter set we use is in line with the recent experimental data ?B??~1.01?0.20+0.18?0.11MeV. It is found that with ?* and mesons the pairing energy gap ?F of ? hyperons and the corresponding SF critical temperature TC?; are suppressed. In addition the NS mass range of ? hyperon SF is enlarged obviously.

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:

A Possible New Effect of Self-Consistency in the Relativistic Hartree-Fock Approximation

A new effect of self-consistency in the relativistic Hartree-Fock (HF) approximation suggested previously is confirmed by a renormalized calculation with the on-shell renormalization conditions. Two self-consistency schemes, one requiring self-consistency in the HF potential (scheme P) and the other in the baryon propagator (scheme BP), are studied. It is pointed out that the on-shell renormalization conditions make the self-consistency requirement in scheme P automatically satisfied. Our calculated results show that scheme P is a good approximation to scheme BP for the calculation of the baryon propagator and the self-consistency in scheme BP diminishes the continuum part of the spectral representation for the baryon propagator, while scheme P yields a baryon propagator which is the same as the HF result contributed by the single particle part of the above spectral representation alone. Further, it is demonstrated that the region of validity of the quasi-particle approximation may depend on the renormalization conditions.

Effects of δ mesons on baryonic direct Urca processes in neutron star matter

This study investigates the relativistic neutrino emissivity of the nucleonic and hyperonic direct Urca processes in the degenerate baryon matter of neutron stars, within the framework of relativistic mean field theory.In particular, we study the influence of the isovector scalar interaction on the nucleonic and hyperonic direct Urca processes by exchanging δ mesons. The results indicate that δ mesons lead to obvious enhancement of the total neutrino emissivity, which must result in a more rapid cooling rate of neutron star matter.This study investigates the relativistic neutrino emissivity of the nucleonic and hyperonic direct Urca processes in the degenerate baryon matter of neutron stars, within the framework of relativistic mean field theory. In particular, we study the influence of the isovector scalar interaction on the nucleonic and hyperonic direct Urca processes by exchanging δ mesons. The results indicate that δ mesons lead to obvious enhancement of the total neutrino emissivity, which must result in a more rapid cooling rate of neutron star matter.In the framework of relativistic mean field theory, the relativistic neutrino emissivity of the nucleonic and hyperonic direct Urca processes in the degenerate baryon matter of neutron stars are studied. We investigate particularly the influence of the isovector scalar interaction which is considered by exchanging