旋转运动磁单极势与辐射能

近来许多工作给出磁单极势与场强的解,其中不少为静止磁单极的球对称解[1].最近的一些工作,讨论了匀加速直线运动磁单极的推迟势与场强[2],此外还给出任意变速运动磁单极势与场强的解[3].本文讨论作旋转运动磁单极的势、场强和辐射能的表示式.磁单极场的势与场强的表示式不同干电荷的场,但具有严格对偶相等的表现形式.至于辐射能,最大的辐射强度将分布在与磁单极旋转平面相垂直的z轴方向,而平行于旋转平面的方向辐射强度为最小. 我们知道,对于一个电荷和一个磁荷共存的体系,真空中的Maxwell方程可写成上式用四维电磁场张量可改写为式中民占…     

双孤子非线性干涉中的狄拉克磁单极势

本文深入研究了孤子干涉过程中的相位演化特性及其背后的拓扑矢势.基于一维非线性薛定谔方程的双孤子解,发现波函数密度零点广泛存在于拓展的复平面内,并且每一个密度零点对应狄拉克磁单极的矢势场.矢势场是由周期排布的具有相反磁荷的狄拉克磁单极对组成.通过观察磁单极子的运动,可以方便地理解干涉过程中的相位演化特征.特别发现,一对正负磁单极对在实轴上的碰撞恰好对应波函数相位在节点处的π跃变.此外,还对比讨论了线性波包干涉动力学中的狄拉克磁单极.结果表明狄拉克磁单极势广泛存在于波场的干涉现象之中,并且磁单极在拓展的复平面内分布特征可用于区分线性干涉和非线性干涉过程背后的拓扑性质.     

磁单极和电磁对偶性

根据狄拉克-麦克斯韦方程组和推广的洛伦兹力公式,讨论了磁单极和电磁对偶性的基本概念和物理意义.麦克斯韦方程组和洛伦兹力公式可以通过对偶变化转化为电荷与磁荷并存的形式;但是狄拉克磁单极假设改变了麦克斯韦方程组的结构,任何对偶变换都不能将狄拉克-麦克斯韦方程组简化为只有电荷而没有磁荷的原始形式.采用推广的洛伦兹力公式,还证明了狄拉克-麦克斯韦电磁场的能量密度和玻印亭矢量,以及动量密度和动量流张量形式不变.最后,我们还将狄拉克-麦克斯韦方程组分解为仅仅分别包含电荷与磁荷的两组麦克斯韦方程,传统的电动力学理论可以直接推广应用于磁单极问题.     

磁单极

在经典电动力学的麦克斯韦方程组中,·D=σf,而·B=0。这意味着和电荷相应的磁荷(磁单极)不存在。因而,在经典的麦克斯韦电磁理论中,电和磁并不处在完全对称的地位。对此,人们不很满意。如果自然界有磁荷存在,那么只要假定所有粒子的磁荷一电荷比是同一常数,总能通过适当的数学变换使麦克斯韦方程组仍具有目前这种形式。 近代对磁单极的讨论始于1931年Dirac的一篇文章[1]。Dirac指出:如果自然界有磁荷存在,则任何粒子的电荷就必须是量子化的,即必须是电子电荷的整数倍。1974年,A,M.polyakov(苏联)和G.t’Hooft(芬兰)又指出:磁单极的质量…     

变速运动磁单极场强的各种表式及磁单极势的积分形式

本文给出了加速运动磁单极场强的严格解.从势的积分定义出发导出了静止、匀速直线运动的磁单极势的具体表达式.讨论了加速磁单极势的形式问题.结果表明,在静止情况下得到吴-杨势.匀速运动情况下的势也可以通过Lorentz变换从吴-杨势得到.但加速运动磁单极的势不可能通过Lorentz变换得到.而加速电子的李纳-维谢尔势却可通过Lorentz变换得到.这表明加速磁荷与电荷有着本质的差异.     

利用非对称核物质状态方程对中子星的质量和半径的研究

在温度、密度及同位旋相关的核物质状态方程的基础上,通过求解Tol-man-Oppenheimer?Volkoff方程得到了中子星的质量与中心密度的关系,发现随着中心密度的变化,中子星存在一个最大质量.同时计算结果表明,中子星的最大质量与核物质状态方程的不可压缩系数、有效质量及对称能强度系数等密切相关.对中子星半径的研究表明,较硬的核物质状态方程给出的中子星半径较大,而且较大的对称能强度系数和较大的核子有效质量也会给出较大的中子星半径.     

电磁学与电动力学中的磁单极—Ⅳ

本文为作者磁单极系列文章的第4篇,该系列文章在电磁学和电动力学框架内用尽量科普的方式分别介绍磁单极的若干奇特性质.在本篇文章中作者讨论用拓扑参量θ描写磁电介质,发现在这种介质上出现了电荷与磁单极作为双荷子共生的现象.如果进一步考虑到磁荷与电荷的量子化,则得到此介质的拓扑参量θ必须是π的分数或整数倍.     

磁单极理论的进展

这是关于磁单极理论最近某些工作的简短 综述.所取得的进展归因于某种观念的引进。 这种观念将时空分为若干个区域,从而消去奇 性 .这个观念是十分简单的,并将首先加以 讨论. (A)如何消除奇性 磁单极就是磁荷.虽然磁单极的概念必然 在经典物理中,在电学和磁学的早期就讨论过, 但是现代的讨论还要追溯到1931年,在狄拉克 的一篇重要文章[1]中,他指出量子力学中的磁 单极显示出某些附加的而且微妙的特征.特别 是,与强度为g的磁单极一起存在时、电荷和磁 荷必须在量子力学中被量子化.我们将用几分 钟的时间对这个结果给出一个新的推导。 如果…     

介质效应对中子星性质的影响

用Bonn势和包含介质修正的相对论平均场模型讨论了介质效应对中子星性质的影响,结果表明BR标度参数的增加导致中子星质量及半径的增加.     

208ΛPb的超子分布半径和中子星结构

从相对论平均场理论出发,考虑核子、超子和介子自由度,研究了208ΛPb的超子分布半径与中子星的性质以及它们之间的关系. 计算发现当超子的耦合常数比值由0.3增大到1时,对NLSH和NL3参数组,超核的超子分布半径分别由3.905和3.849fm增大到4.346和4.230fm,而中子星的最大质量分别由1.516和1.429M⊙增大到2.776和2.744M⊙,质量为1.4M⊙的中子星半径分别由13.13和12.79km增大到13.24和13.29km.即中子星的最大质量和半径随超子分布半径增大而增加. 这样只要从实验上确定208ΛPb的超子分布半径,就可以得到中子星结构的信息.     

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⊙)。     

Magnetic collapse of a neutron gas: Can magnetars indeed be formed?

A relativistic degenerate neutron gas in equilibrium with a background of electrons and protons in a magnetic field exerts its pressure anisotropically, having a smaller value perpendicular to than along the magnetic field. For critical fields the magnetic pressure may produce the vanishing of the equatorial pressure of the neutron gas. Taking this as a model for neutron stars, the outcome could be a transverse collapse of the star. This fixes a limit to the fields to be observable in stable neutron star pulsars as a function of their density. The final structure left over after the implosion might be a mixed phase of nucleons and a meson condensate, a strange star, or a highly distorted black hole or black ”cigar”, but not a magnetar, if viewed as a superstrongly magnetized neutron star. However, we do not exclude the possibility of superstrong magnetic fields arising in supernova explosions which lead directly to strange stars. In other words, if any magnetars exist, they cannot be neutron stars. Received: 25 November 2002 / Revised version: 25 February 2003 / Published online: 5 May 2003     

Pesponse of the Neutron Star Properties to the Equation of State at Low Density

Using the RMF theory to describe the neutron liquid region in the neutron star and the Fermi gas model or FMT, BPS,and BBP model to describe the crust of the neutron star (referred as Fermi gas+RMF and RMF* respectively),the properties of the neutron star are calculated and compared with those from the RMF theory. Although the EOS at low density has negligible influence on the maximum mass of the neutron star, and its corresponding central density, energy density, and pressure, it changes the mass-radius relationship of neutron stars considerably. The differences of the neutron star radius corresponding to maximum mass between the RMF theory and RMF* calculations are 0.23-0.33 km.     

Radial oscillations of neutron stars in strong magnetic fields

The eigen frequencies of radial pulsations of neutron stars are calculated in a strong magnetic field. At low densities we use the magnetic BPS equation of state (EOS) similar to that obtained by Lai and Shapiro while at high densities the EOS obtained from the relativistic nuclear mean field theory is taken and extended to include strong magnetic field. It is found that magnetized neutron stars support higher maximum mass whereas the effect of magnetic field on radial stability for observed neutron star masses is minimal.     

Ultimate energy density of observable cold baryonic matter

We demonstrate that the largest measured mass of a neutron star establishes an upper bound to the energy density of observable cold baryonic matter. An equation of state-independent expression satisfied by both normal neutron stars and self-bound quark matter stars is derived for the largest energy density of matter inside stars as a function of their masses. The largest observed mass sets the lowest upper limit to the density. Implications from existing and future neutron star mass measurements are discussed.     

Structure of Rotating Neutron Stars in Uniform Strong Magnetic Field

Properties and deformations of the rotating neutron stars in uniform strong magnetic field are calculated. The magnetic field will soften the equation of state of the neutron star matters and make an obvious effect on the structure of the rotating neutron star. If the magnetic field is superstrong （B=10^17 T）, the mass, radius, and the deformation will become smaller effectively.     

Influences of the bag constant on properties of hybrid stars

Influences of the bag constant on the properties of hybrid stars are investigated by using relativistic mean field theory and the MIT bag model to describe the hadron phase and quark phase in the interior of neutron stars, respectively. Our results indicate that the onset of hadron-quark phase transition is put off and the appearance of hyperon species is increased with the increase in bag constant. As a result, the hybrid star equation of state for a mixed phase range stiffens whereas that of the quark phase range softens, and the gravitational mass as well as the corresponding radius of hybrid stars are increased obviously. The gravitational mass of a hybrid star is increased from 1.42 Mo (M<,⊙> is solar mass) to 1.63M<,⊙> and the corresponding radius is changed from 9.1 km to 12.2 km when the bag constant (B<'1/4>) is increased from 170 MeV to 200 MeV. It is interesting to find that hybrid star equations of state become non-smooth when the TM2 parameter sets in the framework of relativistic mean field theory used to describe the hadronic matter, and consequently, the third family of compact stars appear in the mass-radius relations of hybrid stars in the narrow scope of the bag constant from 175 MeV to 180 MeV. These show that the choice of the bag constant in the MIT bag model has significant influence on the properties of hybrid stars.     

The character of an anisotropic and spherically symmetric star in the presence of a cosmological constant

From the gravitational structure equations of an anisotropic and spherically symmetric star in the presence of a cosmological constant, we derive the inequality which limits the mass-radius ratio, imposing energy conditions on the matter, From this inequality, we display how the cosmological constant modifies the Buchdahl limit, and express the bounds on both the mass-radius ratio and surface redshiR in terms of the ratio between the cosmological constant and mean energy density of the star.     

Neutron stars including the effects of chaotic magnetic fields and anomalous magnetic moments

The relativistic mean field(RMF) FSUGold model extended to include hyperons is employed to study the properties of neutron stars with strong magnetic fields.The chaotic magnetic field approximation is utilized.The effect of anomalous magnetic moments(AMMs) is also investigated.It is shown that the equation of state(EOS)of neutron star matter is stiffened by the presence of the magnetic field,which increases the maximum mass of a neutron star by around 6%.The AMMs only have a small influence on the EOS of neutron star matter,and increase the maximum mass of a neutron star by 0.02M_(sun).Neutral particles are spin polarized due to the presence of the AMMs.