黑洞及其视界附近的物理规律

 人类对黑洞的认识过程在1796年,法国天文学家拉普拉斯在他的著作《宇宙体系论》中就预言:如果它引力足够强,光速也不足以成为逃逸速度的话,我们可能会看不见它。宇宙中最大的天体可能是完全看不见的,这种观点是建立在牛顿引力理论基础上的,当时没有任何办法能够验证他的想法。直到100年后,爱因斯坦发表了广义相对论,它在基本概念上与牛顿引力理论完全不同。在广义相对论中,空间和时间构成了一个四维时空,时空的几何性质与物质,通过爱因斯坦引力方程联系起来,物质是引力的源,也决定了时空的弯曲。广义相对论发表后不久,德国天文学家史瓦西立即对球对称的情况求出了爱因斯坦引力方程的解。     

观测宇宙的新窗口--2002年度诺贝尔物理学奖介绍

文章介绍了2002年诺贝尔物理学奖获得者贾科尼对X射线天文学的开创性贡献，特别介绍了贾科尼等在开拓空间观测和发展x射线成像技术这两个方面的工作．文章通过x射线天文学的诞生、X射线天文卫星的发展介绍了X射线的空间观测对天体物理学的影响，对宇宙暗物质、双星中的吸积过程和X射线喷流现象等进行了简单介绍，并对高能天体物理学的发展给出了概略的描述．     

旋转致密双星的引力波特征

研究了轨道和旋转效果到2.5阶后牛顿旋转致密双星拉格朗日动力学与引力波的关系, 分析了有序和混沌轨道的引力波特征.发现当加速度不考虑辐射项时, 有序双星系统辐射的引力波具有周期或拟周期的特征, 而混沌双星系统辐射的引力波却具有明显的混沌特征.当加速度含有辐射项贡献时, 双星必会出现并合现象.此时, 原保守有序双星系统需较长时间才能完成并合过程, 引力波形在双星并合前仍保留拟周期的基本特点;然而, 原保守混沌双星系统仅在较短时间内就会并合, 但因并合时间太短, 无法获取足够的动力学信息导致引力波形的特征不易分辨.     

临界转动恒星Achernar的斜压结构与引力昏暗的精细研究

转动和潮汐效应是影响恒星结构和演化的非常重要的物理因素. 根据对Achernar的观测数据, 用扰动理论推导了临界转动恒星Achernar分别作为单星和双星的斜压结构的特征, 给出Achernar等压面上的密度等物理量的分布. 利用考虑转动和潮汐及形变效应的单、双星模型研究了Achernar的引力昏暗现象. 结果表明正剪切增强离心力、减小赤道的重力加速度和温度, 反剪切结果则与之相反. 反剪切和刚性转动情况并不符合对Achernar的引力昏暗观测结果. 发现转动双星模型比单星模型虽更符合Achernar赤道和极半径之比的观测值, 但理论计算的角速度比观测值小. 对比理论计算和观测结果发现, 当Achernar的自转角速度为4.65× 10^-5 s^-1, 正剪切率Ω/Ω_s为0.7851时, Achernar的极点温度为16041 K, 赤道温度为12073 K. 所有理论计算与观测值的相对误差不超过7%.     

ICF实验软X射线能谱仪对辐射能流时间关联测量的时标系统

介绍了时标系统的构成、原理和数据处理方法,并对时间关联的不确定度进行了分析.该时标系统成功将软X射线能谱仪 自身多个探测通道的信号以及三台不同位置处的谱仪的时间信号关联起来,关联精度约为70 ps.在神光III原型激光装置上进行的实验中用软X射线能谱仪从不同方向测得辐射源和辐射输运管末端口辐射能流随时间的演化曲线,反映了输运管内热波沿轴向传输以及软X射线辐射流衰减的物理过程.     

惯性原理及其宇宙起源(下)

 四、常曲率空时惯性原理及其宇宙学意义常曲率空时相对性原理和德西特不变的相对论如何面对暗宇宙的尖锐挑战?为什么我们的宇宙在加速膨胀,一定不渐近平坦,而很可能具有一个正的极小宇宙常数,渐近于德西特空时?而按照通常的处理,德西特空时却带来一系列疑难;极小而又为正的宇宙常数也带来极大困惑。通行的看法是把宇宙常数等同于量子理论中“真空”的能量。可是,这样得到的宇宙常数值比观测值大了一百二十几个量级;考虑种种可能修正、包括超对称等等,也还要大几十个量级。理论与观测之间如此大的差别,前所未有。根本问题出在哪里?通常的作法是考虑种种动力学模型、修改引力场方程,甚至借助量子引力等等。     

从罗伯森到今天的宇宙学

爱因斯坦创立了引力的现代理论——广义相对论.这一理论将引力和宇宙学都几何化了.爱因斯坦本人曾设想过一种空间封闭的定态宇宙.弗里德曼发现(或猜想)了一种爱因斯坦场方程的非定态解.哈勃发现了遥远星系的红移,从而证实了宇宙膨胀演化的观念. 罗伯森采取了一条在逻辑上和数学上都严格的途径.在假定宇宙是严格均匀和各向同性的情况下,他找出了所有可能的“宇宙学”.他的结果和弗里德曼的猜测一致但更为可信. 罗伯森继后还探讨了这个解的所有观测性质:如天体的红移、角大小、亮度等与光从发射到接收所经历的时间的关系. 1965年发现了宇宙微…     

致密双星后牛顿偏心轨道的引力波研究

本文主要研究非保守的后牛顿哈密顿自旋致密双星偏心轨道的引力辐射,数值比较保守的和非保守的自旋致密双星系统轨道参量偏心率大小与 引力波形的关系及引力辐射耗散效应项对轨道动力特性的影响. 数值研究表明：由于系统能量积分被保持,保守的双星轨道偏心率值改变对时域引力波形变化影响不是很明显,但辐射的引力波频率分布范围随着偏心率的增大而扩大. 而当运动方程中包含2.5PN引力耗散效应项时,由于引力辐射时伴随着能量和角动量损失,导致双星两体之间的距离和轨道偏心率逐渐衰减,轨道动力特性变得更加复杂. 双星旋进合并过程中辐射的引力波受到轨道偏心率的调制,引力辐射的强度随着偏心率的增大而增强,而引力辐射持续的时间缩短,且自旋与自旋耦合效应项对引力的贡献增大了. 关键词： 非保守的 引力辐射 耗散 偏心率     

X射线条纹相机紫外光时标研究

 报导了一种采用超短紫外光脉冲作为X 射线条纹相机时标系统的方法。时标光脉冲来自用多模石英光纤耦合的波长为1.06μm 四倍频超短紫外光脉冲激光系统。时标光脉冲与打靶产生的X 射线均被X 射线条纹相机接收, 以用来测定激光打靶时X 射线产生的相对时间关系或相机之间同步的时间关系。实验得到通过光纤引导的时标光脉冲宽度约为30ps。     

空间硬X射线调制望远镜

用宇宙作为物理实验室,探索在地球上无法企及的条件下,例如极早期宇宙或黑洞视界附近强引力场中的物理规律,已成为新世纪物理学和天文学共同的前沿课题;空间天文观测是其中一个最重要的研究途径.自主研制和发放空间硬X射线调制望远镜(HXMT),实现中国空间天文卫星零的突破,是中国<"十一·五"空间科学发展规划>的目标之一.HXMT将实现宽波段X射线(1-250 keV)巡天,其中在硬X射线波段具有世界最高灵敏度和空间分辨率,发现大批被尘埃遮挡的超大质量黑洞和未知类型天体,探测宇宙硬X射线背景辐射;HXMT还将通过对黑洞和其他高能天体宽波段X射线时变和能谱的观测,研究致密天体极端物理条件下的动力学和辐射过程.基于成像技术创新提出HXMT项目迄今已有15年,能不能抓住技术创新所提供的科学机遇仍然是一个严重的挑战.     

Ordinary predictions from grand principles: t-quark mass in O(10)

We elaborate on a model proposed earlier in which the KM mixing angles and the t-quark mass are determined by the structure of the underlying grand unified theory, O(10). We describe the Higgs structure of the model explicitly. We assume that the model involves only two mass scales, the ordinary masses, less than a few hundred GeV, and the grand unification mass ～10¹⁶ GeV. This can lead to interesting phenomenological consequences in the Higgs sector.     

质子衰变实验进展

按照粒子物理标准模型理论,重子数是绝对守恒的.而大统一理论(GUTs)明确地否定了重子数的对称性,预言质子会衰变成更轻的次粒子.文章论述了质子衰变的物理概念、基本探测条件和主要实验现状,并在探测方法的探讨和探测技术的改进方面融入了一些想法.目前一般认为质子的寿命为τp>1032年左右.质子衰变的探测,对于新理论模型的验证、宇宙学和粒子物理学的发展具有重要意义.     

Threshold Corrections to the Minimal SUSY SU(5) Grand Unified Theory

Threshold corrections have been carried out atlow- and high-energy scales to the minimalsupersymmetric SU(5) grand unified theory. More refinedvalues for the Weinberg angle and strong couplingconstant are predicted which are fully consistent withthe latest experimental values.     

Baryon asymmetry and low energy parity restoration

We examine the question of baryon number generation in the early universe in theories with low intermediate mass scales It is shown that the recently proposed O(10) grand unified theory with parity restoration at E ≈ few hundred GeV allows for the creation of matter-antimatter asymmetry in accord with cosmological observations. This evades a recent general argument for incompatibility between weakly broken left-right symmetry and substantial baryon generation.     

Gravitation and spontaneous symmetry breaking

It is pointed out that the Higgs field may be supplanted by an ordinary Klein-Gordon field conformally coupled to the space-time curvature, and with very small, real, rest mass. Provided there is a bare cosmological constant of order of its square mass, this field can induce spontaneous symmetry breaking with a mass scale that can be as large as the Planck-Wheeler mass, but may be smaller. It can thus play a natural role in grand unified theories. In the theory presented here the physical cosmological constant is small, being of order of the squared mass, and can meet observational constraints without having to be cancelled accurately. The physical gravitational constant differs somewhat from the coupling constant in Einstein's equation, and is temperature dependent in the broken symmetry regime. Symmetry restoration occurs at high temperature.Research supported by the Arnow Chair in Astrophysics.     

Spectrum of the supersymmetric Liouville theory

The problem of the monopole infinite moments of inertia, and the related degeneracies in the dyon spectrum of a grand unified theory in the absence of light fermions is considered. A careful application to gauge theories of the method of collective coordinates is given in two different classes of gauges. A basic defect in the earlier treatments of the subject is pointed out. It is shown that the commonly accepted method, while giving reasonable qualitative results for the dyon spectrum in the SO(3) model, fails completely when applied to grand unified theories. The reason is simply that there is a contribution to the monopole moments of inertia that has so far been overlooked. This contribution is of the same order of magnitude as the already known one. The sum of the two contributions vanishes for these moments of inertia that have been thought to be infinite. This means that, in a grand unified theory without light fermions, dyon states transforming as definite color representations (chromodyons) do not exist if we believe this lowest-order analysis (which is almost all what one can do to show their existence). It is shown that applying the Bohr-Sommerfeld method to the classical dyon solutions leads to the same result.     

Intermediate scales in supersymmetric GUTs: the survival of the fittest

We show that intermediate scales in supersymmetric grand unified theories may exist naturally. Their origin is traced to the violation of the survival principle: in supersymmetry internal symmetries often forbid cubic couplings in the superpotential. This leads to a plethora of light supermultiplets whose masses are generated only by higher dimensional operators and thus suppressed by the cut-off scale. These new states often carry exotic quantum numbers and may be, in some cases, accessible to experiments in the near future.     

SU(8) grand unification

A grand unified gauge theory based on the group SU(8) is presented. The set of rules motivating the choice of SU(8) is given. The particle content of the theory suggests a natural embedding of a horizontal SU(3) symmetry in the SU(8) grand unified symmetry.     

Phase transitions at finite chemical potential in grand unified theories

We discuss the circumstances in which non-zero chemical potentials might prevent symmetry restoration in phase transitions in the early universe at grand unification or partial unification scales. The general arguments are illustrated by consideration of SO(10) and SU(5) grand unified theories.     

AN SU(6) GRAND UNIFIED MODEL

A model of grand unified theory based on SU(6) gauge group is proposed. It can accommodate two generations of ordinary fermions with V－A weak coupling and two generations of anomalous fermions with V+A weak coupling. In this model a new discrete symmetry is introduced which insures existence of fermions with lower masses when SU(6) gauge symmetry is spontaneously broken. We choose simple Higgs fields with appropriate vacuum expectation values so that the masses of anomalous fermions are heavier than those of ordinary fermions. This model also gives the same value of Weinberg angle, sin²θw=3/8, as in the usual SU(5) grand unified model at the grand unified scale.