The hyperon coupling constants and the surface gravitational redshift of massive neutron stars

With relativistic mean field theory we examine effect of hyperon coupling constants of hyperon Ξ on the surface gravitational redshift of the massive neutron star (NS) PSR J1614-2230 and NS PSR J0348+0432 as the potential well depth of hyperon Ξ is fixed. We find that the mass and radius of a NS increase with the increase of the coupling constant of hyperon Ξ. With the increase of the coupling constant of the hyperon Ξ, the surface gravitational redshift will decrease for a same NS mass but will increase for a same NS radius. The surface gravitational redshift of the more massive NS PSR J0348+0432 decreases by more than that of the less massive NS PSR J1614-2230. We also find that the value range of the surface gravitational redshift of NS will become narrower with the increase of the coupling constant of hyperon Ξ. The greater the NS mass, the greater the influence of the coupling constant of hyperon Ξ on the value range of the surface gravitational redshift of the NS.     

Gravitational waves from the axial perturbations of hyperon stars

The eigen-frequencies of the axial w-mode oscillations of hyperon stars are examined.It is shown that as the appearance of hyperons softens the equation of state of the super-density matter,the frequency of gravitational waves from the axial w-mode of hyperon star becomes smaller than that of a traditional neutron star at the same stellar mass.Moreover,the eigenfrequencies of hyperon stars also have scaling universality.It is shown that the EURO thirdgeneration gravitational-wave detector has the potential to detect the gravitational-wave signal emitted from the axial w-mode oscillations of a hyperon star.     

Hypernuclear physics for neutron stars

The role of hypernuclear physics for the physics of neutron stars is delineated. Hypernuclear potentials in dense matter control the hyperon composition of dense neutron star matter. The three-body interactions of nucleons and hyperons determine the stiffness of the neutron star equation of state and thereby the maximum neutron star mass. Two-body hyperon–nucleon and hyperon–hyperon interactions give rise to hyperon pairing which exponentially suppresses cooling of neutron stars via the direct hyperon URCA processes. Nonmesonic weak reactions with hyperons in dense neutron star matter govern the gravitational wave emissions due to the r-mode instability of rotating neutron stars.     

Constraining the Surface Gravitational Redshift of Proto Neutron Stars with New Nucleon Coupling Constants

A new set of nucleon coupling constants (CZ11) is obtained for the relativistic mean field (RMF) theory based on the recent experimental information on the symmetry energy derived from the data from NSCL/MSU. The surface gravitational redshift of a proto neutron star (PNS) is examined within the RMF framework for the baryon octet system by using this set of parameters. It is found that the surface gravitational redshift for CZ11 is smaller than that for GL97. For the CZ11 parameter set, the surface gravitational redshift of a PNS at T=15 MeV is smaller than that at T=0 MeV. It is also found that the surface gravitational redshift corresponding to M _max/R for the CZ11 parameter set is smaller by about 10 percent than that for GL97, with M _max being the maximum mass and R being the corresponding radius.     

Bose-Einstein condensation of anti-kaons and neutron star twins

We investigate the role of Bose-Einstein condensation (BEC) of anti-kaons on the equation of state (EoS) and other properties of compact stars. In the framework of relativistic mean field model we determine the EoS for β-stable hyperon matter and compare it to the situation when anti-kaons condense in the system. We observe that anti-kaon condensates soften the EoS, thereby lowering the maximum mass of the stars. We also demonstrate that the presence of antikaon condensates in the high density core of compact stars may lead to a new mass sequence beyond white dwarf and neutron stars. The limiting mass of the new sequence stars is nearly equal to that of neutron star branch though they have distinctly different radii and compositions. They are called neutron star twins.     

核物质对称能斜率对快转中子星性质的约束（英文）

在过去的十余年中,对非对称核物质的对称能的研究无论从实验还是理论上都取得了较大的突破,这对中子结构及其物态方程的理解具有十分重要的意义。本研究将采用一个相对保守的对称能斜率范围(25 Me VL105Me V)来研究其对快速转动中子星性质的约束,这些性质包括:质量-半径关系、转动惯量、引力红移以及转动形变等。通过该对称能斜率的约束,发现典型中子星(M=1.4M⊙)的半径约束在10.28～13.43 km范围内,这与最近的相关观测相一致。如果观察发现了质量较小的毫秒脉冲星,则将为核物质的对称能较软提供有效的证据。另外还发现,对角动量的一致性可为快转中子星转动惯量的上限提供约束。最后,根据具有低质量伴星的双星EXO0748-676的红移观测,给出了该脉冲星的质量下限(1.5M⊙)。     

超子耦合常数对混合星性质的影响

用相对论平均场理论描述强子物质, 用NJL模型描述夸克物质研究了超子耦合常数对混合星性质的影响. 结果表明, 随着超子耦合常数的增大, 强子-夸克相变密度变小, 混合相区域的状态方程变硬, 中子星的最大质量及对应的半径变大. 超子耦合常数由0.73增到1.0时, 混合星最大质量由1.68M_⊙增至1.84M_⊙, 相应的半径由11.4km变到12.5km. 该夸克模型下不同强子参数组对应的混合星性质也有较明显的差异. 可知, 其适合于描述大质量而小夸克核心的混合星.     

Effect of f0(975) and φ(1020) Mesons on Neutron Star Mater

In the RMF approach, considering the contributions of the σ^* and φ mesons and the hyperons in the baryon octet {N,P,Λ,∑^－,∑⁰,∑⁺,Ξ^－,Ξ⁰}, the properties of neutron star matter have been investigated. It is found that with the contributions of the σ^* and φ mesons, the critical baryon density of hyperon appearance decreases, the number of hyperons increases, the transition density ρ_0H of hyperon stars decreases, the equation of state turns soft, the maximum mass of neutron star decreases and the corresponding radius increases, the central density, the central energy density and the central pressure are all reduced.     

L_2-L_∞ learning of dynamic neural networks

This paper proposes an L2 -L∞ learning law as a new learning method for dynamic neural networks with external disturbance. Based on linear matrix inequality (LMI) formulation, the L2-L∞ learning law is presented to not only guarantee asymptotical stability of dynamic neural networks but also reduce the effect of external disturbance to an L2-L∞ induced norm constraint. It is shown that the design of the L2-L∞ learning law for such neural networks can be achieved by solving LMIs, which can be easily facilitated by using some standard numerical packages. A numerical example is presented to demonstrate the validity of the proposed learning law.     

Gravitational redshift of gravitational clocks

The gravitational redshift of gravitational clocks in a given weak gravitational field, within general relativity, is considered. Because the clocks in question have structure and dynamics determined by gravitational interactions, the full machinery of Einstein's equations must be used. Three specific examples are treated: (i) the redshift of the angular frequency of a rotating relativistic star in the gravitational field of a distant body; (ii) the redshift of the angular velocity of a slowly rotating black hole surrounded by an axisymmetric ring of matter; and (iii) the redshift of the observed orbital period of a nearly circular, post-Newtonian binary system in the field of a distant, third body. In all three cases the redshift is the same as if the clocks were non-gravitational, thereby governed by the Einstein equivalence principle. For an observer at infinity, the redshift $\text{Z ≡}\text{Δv}\text{v}$ is given by $\text{Z =}\text{?Gm}\text{Rc}{}^2$, where m is the mass of the distant object and R its distance from the clock in question. The result is independent of how relativistic the clock may be. The significance of this conclusion for the binary pulsar PSR 1913 + 16, where the gravitational redshift of the pulsar's frequency caused by the gravitational field of its companion is an observable effect, is discussed. The extent to which this result is a manifestation of the strong equivalence principle, satisfied, as far is known, only by general relativity, is also noted.     

Kaon properties in (proto-)neutron star matter

The modification of kaon and antikaon properties in the interior of (proto-)neutron stars is investigated using a chiral SU(3) model. The parameters of the model are fitted to nuclear-matter saturation properties, baryon octet vacuum masses, hyperon optical potentials and low-energy kaon-nucleon scattering lengths. We study the kaon/antikaon medium modification and explore the possibility of antikaon condensation in (proto-)neutron star matter at zero as well as finite temperature/entropy and neutrino content. The effect of hyperons on kaon and antikaon optical potentials is also investigated at different stages of the neutron star evolution.     

Thermal activation of current in an inhomogeneous Schottky diode with a Gaussian distribution of barrier height

This paper investigates the thermal activation behaviour of current in an inhomogeneous Schottky diode with a Gaussian distribution of barrier height by numerical simulation. The analytical Gaussian distribution model predicted that the I--V--T curves may intersect with the possibility of the negative thermal activation of current, but may be contradictory to the thermionic emission mechanism in a Schottky diode. It shows that the cause of the unphysical phenomenon is related to the incorrect calculation of current across very low barriers. It proposes that junction voltage V_j, excluding the voltage drop across series resistance from the external bias, is a crucial parameter for correct calculation of the current across very low barriers. For correctly employing the thermionic emission model, V_j needs to be smaller than the barrier height Ф. With proper scheme of series resistance connection where the condition of V_j > Ф is guaranteed, I--V--T curves of an inhomogeneous Schottky diode with a Gaussian distribution of barrier height have been simulated, which demonstrate normal thermal activation. Although the calculated results exclude the intersecting possibility of I--V--T curves with an assumption of temperature-independent series resistance, it shows that the intersecting is possible when the series resistance has a positive temperature coefficient. Finally, the comparison of our numerical and analytical results indicates that the analytical Gaussian distribution model is valid and accurate in analysing I--V--T curves only for small barrier height inhomogeneity.     

Relativistic star clusters with high central redshift

Collisionless star clusters in dynamical equilibrium are of current interest in general relativity and astrophysics. A step-function distribution is chosen for star clusters. The corresponding equation of state is analogous to a Fermi-gas equation. These clusters are found to be pulsationally unstable for a central redshift ofZ _c ⩾ 0·54. Further, a model of clusters is developed in which the core has an extremely relativistic equation of state. These structures are unstable forZ _c ⩾ 2·55 when we use Chandrasekhar’s technique to study their pulsational stability.     

Structure of neutron-rich Λ hypernuclei

Properties of light neutron-rich Λ hypernuclei (¹⁶ _ΛC, ¹² _ΛBe, and ¹¹ _ΛLi) are calculated within the Skyrme-Hartree-Fock approach. Interplay between hypernuclear interaction features and properties of these hypernuclei is studied. Response of weakly bound neutron states to hyperon addition depends generally on core distortion by hyperon, and it is essentially different for the different states. This response is especially sensitive to details of the ΛN interaction for 1p _1/2 states. Implications of the nuclear spin-orbit potential and nuclear incompressibility in the neutron-rich system properties are inferred. Dependence of the Λ binding energies in hypernuclei on Z at fixed A is discussed. Received: 16 December 1998     

Mass and stability of rigidly rotating relativistic polytropes by energy method

The energy of a rigidly rotating star is written in the first and second post-Newtonian approximation. Conditions for equilibrium and stability are derived, as well as evolutionary paths for stars shedding angular momentum or mass. For polytropic index n > 1, these analytic results agree with exact numerical results to within a few percent as long as the general relativity index (P/c²)_c < 0.1. The energy method is applied to low mass white dwarfs, to semirelativistic neutron stars and to supermassive stars.     

Phase transition to color-flavor-locked matter and condensation of Goldstone bosons in neutron star matter

Deconfinement phase transition and condensation of Goldstone bosons in neutron star matter are investigated in a chiral hadronic model (also referred as to the FST model) for the hadronic phase (HP) and in the color-flavor-locked (CFL) quark model for the deconfined quark phase. It is shown that the hadronic-CFL mixed phase (MP) exists in the center of neutron stars with a small bag constant, while the CFL quark matter cannot appear in neutron stars when a large bag constant is taken. Color superconductivity softens the equation of state (EOS) and decreases the maximum mass of neutron stars compared with the unpaired quark matter. The K⁰ condensation in the CFL phase has no remarkable contribution to the EOS and properties of neutron star matter. The EOS and the properties of neutron star matter are sensitive to the bag constant B, the strange quark mass m_s and the color superconducting gap Δ. Increasing B and m_s or decreasing Δ can stiffen the EOS which results in the larger maximum masses of neutron stars.     

Hyperon coupling dependence of hadron matter properties in relativistic mean field model

The properties of hadronic matter at β equilibrium in a wide range of densities are described by appropriate equations of state in the framework of the relativistic mean field model. Strange meson fields, namely the scalar meson field σ＊（975） and the vector meson field φ（1020）, are included in the present work. We discuss and compare the results of the equation of state, nucleon effective mass, and strangeness fraction obtained by adopting the TM1, TMA, and GL parameter sets for nuclear sector and three different choices for the hypcron couplings. We find that the parameter set TM1 favours the onset of hyperons most, while at high densities the GL parameter set leads to the most hyperon-rich matter. For a certain parameter set （e.g. TM1）, the most hyperon-rich matter is obtained for the hyperon potential model. The influence of the hyperon couplings on the effective mass of nucleon, is much weaker than that on the nucleon parameter set. The nonstrange mesons dominate essentially the global properties of dense hyperon matter. The hyperon potential model predicts the lowest value of the neutron star maximum mass of about 1.45 Msun to be 0.4--0.5 Msun lower than the prediction by using the other choices for hyperon couplings.[第一段]     

Constraints on the properties of the massive neutron star PSR J0348+0432 from the f0(975) and φ(1020) mesons

The effect of the f ₀(975) and φ(1020) mesons on the properties of the massive neutron star PSR J0348+0432 is examined in the framework of the relativistic mean-field theory by choosing the suitable hyperon coupling constants. It is found that, compared with that without the f ₀(975) and φ(1020) mesons, the radius of the neutron star PSR J0348+0432 increases from R = 12.072 km to R = 12.08 km (i.e. by 0.07%), the central energy density ? _c decreases from 5.6695 fm^?4 to 5.6492 fm^?4 (i.e. by 0.36%), the central pressure decreases from 1.585 fm^?4 to 1.58 fm^?4 (i.e. by 0.32%), the moment of inertia increases from 1.4592 × 10⁴⁵ g · cm² to 1.4615 × 10⁴⁵ g · cm² (i.e. by 0.16%) and the surface gravitational redshift decreases from z = 0.4026 to z = 0.4022 (i.e. by 0.1%). Our results show that the effect of the f ₀(975) and φ(1020) mesons on the properties of the massive neutron star PSR J0348+0432 is very small (i.e. no more than 0.5%) and therefore they do not play a major role.     

Be-composition effect on structure, electronic and optical properties of BexZn1-xO alloys

This paper carries out first principles calculation of the structure,electronic and optical properties of Be x Zn 1 x O alloys based on the density-functional theory for the compositions x = 0.0,0.25,0.5,0.75,1.0.The lattice constants deviations of alloys obey Vegard’s law well.The Be x Zn 1 x O alloys have the direct band gap(Γ-Γ) character,and the bowing coefficients are less than the available theoretical values.Moreover,it investigates in detail the optical properties(dielectric functions,absorption spectrum and refractive index) of these ternary mixed crystals.The obtained results agree well with the available theoretical and experimental values.