Superfluidity of neutron matter: (II). Triplet pairing

The possibility of neutron triplet pairing and superfluidity in neutron star matter is investigated, and the energy gap and corresponding critical temperature is calculated or estimated as a function of Fermi momentum or density. The calculations are performed for a “one-pion-exchange gaussian” potential, and compared with the results for neutron and proton singlet pairing and superfluidity calculated earlier.The results indicate that neutron superfluidity, corresponding specifically to ³P₂ state pairing, may exist in a high-density shell in the nuclear-matter region of a neutron star, i.e. for 1.6 × 10¹⁴g/cm³ < ρ < 1.4 × 10¹⁵g/cm³, and the maximum self-consistent energy gap is Δ⁰₁k_F ≈ 0.6 MeV and Δ⁰₃(k_F) ≈ 0.1 MeV for an effective mass $\text{m}{}^1\text{≈ 0.75}\text{and}\text{k}{}_{\mathrm{<mtext>F</mtext>}}\text{≈ 2.1}\text{fm}{}^{\mathrm{?1}}$, i.e. for a mas ? ≈ 5.2 × 10¹⁴g/cm³. For $\text{m}{}^1\text{= 1.0}$ we get correspondingly Δ⁰₁(k_F) ≈ 3.3 MeV and Δ⁰₃(k_F) ≈ 0.6 MeV for k_F ≈ 2.2 fm^?1.     

Superfluidity in neutron stars

Arguments are presented to show that the BCS theory of superfluidity in its original form may not be applicable to neutron star matter over a wide range of density.     

Superfluidity in neutron matter and symmetric nuclear matter and the effect of a microscopic three-body force

The neutron ³PF₂ pairing gap in pure neutron matter, neutron ³PF₂ gap and neutron-proton ³SD₁ gap in symmetric nuclear matter have been studied by using the Brueckner-Hartree-Fock(BHF) approach and the BCS theory. We have concentrated on investigating and discussing the three-body force effect on the nucleon superfluidity. The calculated results indicate that the three-body force enhances remarkably the ³PF₂ superfluidity in neutron matter. It also enhances the ³PF₂ superfluidity in symmetric nuclear matter and its effect increases monotonically as the Fermi-momentum k_F increases, whereas the three-body force is shown to influence only weakly the neutron-proton ³SD₁ gap in symmetric nuclear matter.     

Superfluidity in ultra-relativistic quark matter

Possible forms of superfluid order parameter are discussed for quark matter at densities where the Fermi energy is much greater than the mass of the quarks. Ginzburg-Landau equations for the order parameter are derived and solved.     

Superfluidity in dense nuclear matter

We discuss the onset of superfluidity in neutron stars, where the model of nuclear matter is realized in a high-density and asymmetry state. In particular, we present the study of the effects of microscopic three-body forces on the proton pairing in the ¹ S ₀ channel and neutron pairing in ³ PF ₁ channel for β-stable neutron star matter. It is found that the main effects of three-body forces are to shrink the domain of existence of the ¹ S ₀ below the threshold of the direct URCA process and to stretch the density range of the ³ PF ₁ pairing in a broad domain so to cover most part of the neutron-star core. The text was submitted by the authors in English.     

Superfluidity in the inner crust of neutron stars

We present a mean-field quantum calculation of the specific heat in the inner crust of neutron stars, taking into account the inhomogeneous character of the system, in which a lattice of neutron-rich nuclei coexists with a gas of unbound neutrons.Received: 10 December 2002, Published online: 24 February 2004PACS: 21.60.-n Nuclear structure models and methods - 26.60. + c Nuclear matter aspects of neutron stars - 97.60.Jd Neutron stars     

Zero sound in dense neutron matter

Propagation of zero sound in dense neutron matter is investigated within the framework of the Landau theory of normal Fermi liquids. The effect of the spin polarization of the medium is studied. A calculation performed using the quasi-particle interaction derived from the Reid soft-core nucleon-nucleon potential shows that zero sound can propagate in neutron matter for densities greater than $\text{?}{}^1\text{≈ 0.4–0.5}\text{neutrons/fm}{}^3$, and is strongly damped at densities below ?¹.     

Neutrino opacity in cold neutron matter

The weak dynamic form factors of cold neutron matter have been calculated within correlated basis function (CBF) theory using a realistic Hamiltonian. The results show that the effect of nucleon-nucleon correlations on the density and spin-density responses are different. The role of long-range correlations has been investigated comparing the CBF responses to those resulting from Landau theory of Fermi liquids. The neutrino mean free path has been obtained combining the two approaches. The text was submitted by the authors in English.     

Magnetic properties of neutron matter

The energy of interacting neutron matter with spin polarization is calculated in Hartree-Fock approximation by the method of unitary transformations for a hard core and a soft core potential. In addition the magnetic spin susceptibility is given and the possibility of a ferromagnetic transition investigated. It is shown that the effect of the nuclear forces for all densities considered depresses the magnetic spin susceptibility relative to that of the corresponding ideal Fermi gas.     

Specific heat of the superfluid neutron matter in neutron star crusts

By means of X-γ andγ-γ coincidence measurements of the³⁵Cl+⁵⁸Ni reaction products, 38γ lines have been identified to be in coincidence with KX(Tc)-rays and assigned to the decay of⁹⁰Ru. Its half-life of 11±3 s has been deduced from the 154.6 keVγ-decay. The result supports our previous identification of⁹⁰Ru produced in the same reactions.     

Effect of accelerated matter in neutron optics

Results of experiments aimed at observing the change in the energy of a neutron traversing an accelerated refractive sample are reported. The experiments were performed with ultracold neutrons, the energy transfer in these experiments being ±(2?6) × 10^?10 eV. The results suggest the existence of the effect and agree with theoretical predictions to a precision higher than 10%. A similar effect was previously predicted for the change in the frequency of an electromagnetic wave traversing an accelerated dielectric slab. In all probability, the effect has a very general nature, but it is presently observed only in neutron optics.     

Deconfinement phase transition in neutron star matter

The transition from hadron phase to strange quark phase in dense matter is investigated. Instead of using the conventional bag model in quark sect, we achieve the confinement by a density-dependent quark mass derived from in-medium chiral condensates, with a thermodynamic problem improved. In nuclear slot, we adopt the equation of state from Brueckner-Bethe-Goldstone approach with three-body force. It is found that the mixed phase can occur, for reasonable confinement parameter, near the normal saturation density, and transit to pure quark matter at 4-5 times the saturation, which is quite different from the previous results from other quark models that pure quark phase can not appear at neutron-star densities.