高红移Ⅰ_a型超新星的搜寻和宇宙的加速膨胀

观测研究表明,Ⅰａ型超新星可以作为宇宙距离测量的标准光源．天文学家还从近邻Ⅰａ型超新星光变的研究中得出可靠地确定其最高光度的方法．在此基础上,国际上两个相互竞争的研究集体经过几年的不懈努力,对高红移超新星进行了搜寻和观测．他们各自独立地得到了相同的结论：宇宙学常数Λ＞０,宇宙在加速膨胀．这项研究结果将对宇宙学,星系和大尺度结构的形成和演化的研究产生重要影响．更重要的是,它把所谓“宇宙学常数问题”提到我们面前,不再能够回避．而这一问题的解决将有可能带来基础研究上的重大突破     

轴子--粒子物理和宇宙学的新前沿

—、引言粒子物理、宇宙学和天文学的深度结合催生了当下粒子宇宙学研究的高速发展。继2017年引力波之后,2019的物理学诺贝尔奖再次光顾了宇宙学领域,并颁给了从事宇宙学理论研究的Peebles教授。目前,正当宇宙学研究在观测层面大步前进时,理论家和实验家们近年来将目光投向新的宇宙学热点,一个长期被理论预言的基本粒子“轴子(Axion)”。     

哈勃常数危机

哈勃常数定量刻画了当前宇宙的膨胀速率,精确测定哈勃常数是现代宇宙学的一个重要科学问题.近年来,哈勃常数的局域直接测量值与全局模型拟合值之间出现了越来越严重的偏差,其中局域直接测量值来自于晚期宇宙的局域距离阶梯测量结果,而全局模型拟合值来自于早期宇宙的微波背景辐射对宇宙学标准模型的观测限制.如果该偏差不是由其中任何一种观测手段的观测误差和系统误差所致,那么很有可能意味着存在超出宇宙学标准模型的新物理.本文从观测和模型两方面简述该哈勃常数危机问题,并结合作者近年来对此问题的研究从观测和模型两方面进行展望.     

90年代天体物理对物理学的挑战

论述了现代天体物理与物理学的密切关系，进而介绍了９０年代天体物理的新望远镜和新观测设备，概要地论述了９０年代天体物理的重要发现和重大事件，并重点讨论了宇宙学的新进展，最后论述了未来天体物理的主攻方向。     

解读宇宙的起源——2006年诺贝尔物理学奖简介

 2006年度诺贝尔物理奖授予了在宇宙学研究领域取得杰出成果的美国科学家约翰·马瑟和乔治·斯穆特。他们发现的宇宙微波背景辐射的黑体谱和各向异性强烈地支持了大爆炸宇宙学模型并开启了“精确宇宙学”时代的大门。COBE之后宇宙学研究取得了一系列重大的进展。近年WMAP、SDSS等天文观测更加坚实有力地支持了大爆炸宇宙学模型，并对物理学提出了一些重大的、尖锐的挑战，诸如什么是暗物质？暗能量的物理本质是什么？     

哈勃常数和现代宇宙学

在介绍2009年格鲁伯宇宙学奖、简述现代观测宇宙学和哈勃常数的研究简史后,论述用哈勃空间望远镜研究哈勃常数和哈勃图在宇宙学中的应用.     

关于宇宙学常数问题的知识要点和几点思考

大爆炸宇宙学告诉我们,宇宙正在膨胀。如果我们的宇宙主要包含的是基本粒子型物质,那么宇宙将是减速膨胀。但是,对于今天我们观测到的宇宙来说,发现它在最近过去的几十亿年间却在加速膨胀!这预示着,宇宙中的主要能量形态不是基本粒子型物质,而是某种新的能量形态。对这种“新的”能量形态,其实科学家早有察觉和分析。它的最简单的可能性就是宇宙学常数。然而宇宙学常数的物理本质和内容却并不简单。这篇短文,就是主要介绍了宇宙学常数的一些基本知识和我们对它的一些思考。爱因斯坦方程中最自然出现的一项是宇宙学常数(简称cc)项,cc的值任意…     

爱因斯坦的等效原理和广义相对性原理——问题实质和出路

精确宇宙学的观测表明,物理学必须面对以宇宙常数为特征的宇宙尺度。 有关宇宙观测的数据分析,是以广义相对论和宇宙学原理为基础的。然而,分析的结果却向爱因斯坦相对论体系和量子理论,以及以之为基础的现代物理学提出重大疑难。这是对物理学前所未有的、更为严重的全面挑战。     

宇宙中的暗物质

在回顾20世纪物理学基础研究的进展时，宇宙学理论的确立被人们看作是最重大的收获之一．对于年龄达140亿年的宇宙，我们已能把它从若干分之一秒起的演化历史娓娓道出，并且在几乎所有的关键点上找到了观测证据．这确实不能不说它是人类智慧的值得骄傲的成就．近几年来，宇宙学的实测研究又有了一个重要新进展．WMAP卫星通过对早期宇宙中温度起伏的测量，     

物理学和天文学

历史上，物理学和天文学的发展是密切联系的。它们在整个现代科学的发展和技术的发达上起到了先锋的作用。物理学的基本规律和天文学提供的广亵的实验室构成了理想的科学发展的基础。20世纪的一系列科学上的重要突破正是这种优良结合的产物。今天，天文学和物理学又共同面对着更新的前测问题，并一道酝酿着新的科学上的重大进展。它们所取得的每一个进展也必然伴随着技术的创新和提高，也不断更新着人类的认识和文明。     

Gravitational coupling and dynamical reduction of the cosmological constant

We introduce a dynamical model to reduce a large cosmological constant to a sufficiently small value. The basic ingredient in this model is a distinction which has been made between the two unit systems used in cosmology and particle physics. We have used a conformal invariant gravitational model to define a particular conformal frame in terms of large scale properties of the universe. It is then argued that the contributions of mass scales in particle physics to the vacuum energy density should be considered in a different conformal frame. In this manner, a decaying mechanism is presented in which the conformal factor appears as a dynamical field and plays a key role to relax a large effective cosmological constant. Moreover, we argue that this model also provides a possible explanation for the coincidence problem.     

Localization of Gravity in Brane World with Arbitrary Extra Dimensions

We study the induced 4-dimensional linearized Einstein field equations in an m-dimensional bulk space by means of a confining potential. We used the confining potential in this model to localized gravitons on the brane. It is shown that in this approach the mass of graviton is quantized. The cosmological constant problem is also addressed within the context of this approach. We show that the difference between the values of the cosmological constant in particle physics and cosmology stems from our measurements in two different scales, small and large.     

The solution of the cosmological constant problem from the inhomogeneous equation of state — a hint from modified gravity?

The cosmological constant problem is studied in a two component cosmological model. The universe contains a cosmological constant of an arbitrary size and sign and an additional component with an inhomogeneous equation of state. It is shown that, in a proper parameter regime, the expansion of the universe with a large absolute value of the cosmological constant may asymptotically tend to de Sitter space corresponding to a small effective positive cosmological constant. It is argued that such a behavior can be regarded as a solution of the cosmological constant problem in this model. The mechanism behind the relaxation of the cosmological constant is discussed. A connection with modified gravity theories is discussed and an example of a possible realization of the cosmological constant relaxation in f(R) modified gravity is described.     

Large numbers hypothesis. IV. The cosmological constant and quantum physics

In standard physics quantum field theory is based on a flat vacuum space-time. This quantum field theory predicts a nonzero cosmological constant. Hence the gravitational field equations do not admit a flat vacuum space-time. This dilemma is resolved using the units covariant gravitational field equations. This paper shows that the field equations admit a flat vacuum space-time with nonzero cosmological constant if and only if the canonical LNH is valid. This allows an interpretation of the LNH phenomena in terms of a time-dependent vacuum state. If this is correct then the cosmological constant must be positive.     

Working group report: Astroparticle and neutrino physics

The working group on astroparticle and neutrino physics at WHEPP-9 covered a wide range of topics. The main topics were neutrino physics at INO, neutrino astronomy and recent constraints on dark energy coming from cosmological observations of large scale structure and CMB anisotropy.     

Conformal Invariance, Accelerating Universe and the Cosmological Constant Problem

We investigate a conformal invariant gravitational model which is taken to hold at early universe. The conformal invariance allows us to make a dynamical distinction between the two unit systems (or conformal frames) usually used in cosmology and elementary particle physics. In this model we argue that when the universe suffers phase transition, the resulting mass scale introduced by particle physics should have a variable contribution to vacuum energy density. This variation is controlled by the conformal factor which is taken as a dynamical field. We then deal with the cosmological consequences of this model. In particular, we shall show that there is an inationary phase at early times. At late times, on the other hand, it provides a mechanism which makes a large effective cosmological constant relax to a sufficiently small value. Moreover, we shall show that the conformal factor acts as a quintessence field that leads the universe to accelerate at late times.     

ESSAY: The Cosmological Constant Problem in Brane-Worlds and Gravitational Lorentz Violations

Brane worlds are theories with extra spatial dimensions in which ordinary matter is localized on a (3+1) dimensional submanifold. Such theories could have interesting consequences for particle physics and gravitational physics. In this essay we concentrate on the cosmological constant (CC) problem in the context of brane worlds. We show how extra-dimensional scenarios may violate Lorentz invariance in the gravity sector of the effective 4D theory, while particle physics remains unaffected. In such theories the usual no-go theorems for adjustment of the CC do not apply, and we indicate a possible explanation of the smallness of the CC. Lorentz violating effects would manifest themselves in gravitational waves travelling with a speed different from light, which can be searched for in gravitational wave experiments.     

The cosmological constant and dark energy in braneworlds

We review recent attempts to address the cosmological constant problem and the late-time acceleration of the Universe based on braneworld models. In braneworld models, the way in which the vacuum energy gravitates in the 4D spacetime is radically different from conventional 4D physics. It is possible that the vacuum energy on a brane does not curve the 4D spacetime and only affects the geometry of the extra-dimensions, offering a solution to the cosmological constant problem. We review the idea of supersymmetric large extra dimensions that could achieve this and also provide a natural candidate for a quintessence field. We also review the attempts to explain the late-time accelerated expansion of the universe from the large-distance modification of gravity based on the braneworld. We use the Dvali–Gabadadze–Porrati model to demonstrate how one can distinguish this model from dark energy models in 4D general relativity. Theoretical difficulties in this approach are also addressed.