Inflation,Cosmic Perturbations and Non-Gaussianities

We review the theory of inflationary perturbations. Perturbations at both linear and nonlinear orders are reviewed. We also review a variety of inflation models, emphasizing their signatures on cosmic perturbations.     

Non-Gaussianity of Racetrack Inflation Models

In this paper, we use the result in [C.Y. Sun and D.H. Zhang, arXivastro-ph/0510709] to calculate the non-Gaussianity of the racetrack models in[J.J. Blanco-Pillado, et al., JHEP 0411 (2004) 063; arXivhep-th/0406230]and [J.J. Blanco-Pillado, et al., arXivhep-th/0603129]. The two models give different non-Gaussianities. Both of them are reasonable. However, we find that, for multi-field inflationary models with the non-trivial metric of the field space,the condition of the slow-roll cannot guarantee small non-Gaussianities.     

Non-Gaussianity of Racetrack Inflation Models

In this paper, we use the result in [C.Y. Sun and D.H. Zhang, arXiv:astro-ph/0510709] to calculate the non-Gaussianity of the racetrack models in [J.J. Blanco-Pillado, et al., JHEP 0411 (2004) 063; arXiv:hep-th/0406230] and [J.J. Blanco-Pillado, et al., arXiv:hep-th/0603129]. The two models give different non-Gaussianities. Both of them are reasonable. However, we find that, for multi-field inflationary models with the non-trivial metric of the field space, the condition of the slow-roll cannot guarantee small non-Gaussianities.     

Inflation without Selfreproduction

We find a rather unique extension of inflationary scenario which avoids selfreproduction and thus resolves the problems of multiverse, predictability and initial conditions. In this theory the amplitude of the cosmological perturbations is expressed entirely in terms of the total duration of inflation.     

Cosmic phase transitions

The sequence of phase transitions during the hot history of the universe is followed within a phenomenological framework. Particular emphasis is put on the QCD confinement transition, which is at reach under earth laboratory conditions. A tepid inflationary scenario on the GUT scale with bubble growth at moderate supercooling is discussed.     

Cosmic Microwave Background and Inflation Parameters

We review the current cosmic parameter determinations of relevance to inflation using the WMAP-1 year, Boomerang, CBI, Acbar, and other CMB data. The basic steps in the pipelines which determine the bandpowers from the raw data from which these estimations are made are summarized. We forecast how the precision is likely to improve with more years of WMAP in combination with future ground-based experiments and with Planck. We address whether the current data indicates strong breaking from uniform acceleration through the relatively small region of the inflaton potential that the CMB probes, manifest in the much-discussed running spectral index or in even more radical braking/breaking scenarios. Although some weak anomalies appear in the current data, the statistical case is not there. However increased precision, at the high multipole end and with polarization measurements, will significantly curtail current freedom.     

Coupled Criticality Analysis of Inflation and Unemployment

In this paper, we focus on the critical periods in the economy that are characterized by unusual and large fluctuations in macroeconomic indicators, like those measuring inflation and unemployment. We analyze U.S. data for 70 years from 1948 until 2018. To capture their fluctuation essence, we concentrate on the non-Gaussianity of their distributions. We investigate how the non-Gaussianity of these variables affects the coupling structure of them. We distinguish “regular” from “rare” events, in calculating the correlation coefficient, emphasizing that both cases might lead to a different response of the economy. Through the “multifractal random wall” model, one can see that the non-Gaussianity depends on time scales. The non-Gaussianity of unemployment is noticeable only for periods shorter than one year; for longer periods, the fluctuation distribution tends to a Gaussian behavior. In contrast, the non-Gaussianities of inflation fluctuations persist for all time scales. We observe through the “bivariate multifractal random walk” that despite the inflation features, the non-Gaussianity of the coupled structure is finite for scales less than one year, drops for periods larger than one year, and becomes small for scales greater than two years. This means that the footprint of the monetary policies intentionally influencing the inflation and unemployment couple is observed only for time horizons smaller than two years. Finally, to improve some understanding of the effect of rare events, we calculate high moments of the variables’ increments for various q orders and various time scales. The results show that coupling with high moments sharply increases during crises.     

第二讲 宇宙微波背景辐射

简单介绍了近年来关于宇宙微波背景辐射在观测上取得的重大进展,以及有关它的解释、理论和意义.宇宙微波背景是我们了解宇宙奥秘的一个至关重要的窗口.在未来几年,它还将扮演更加重要的角色.     

第二讲宇宙微波背景辐射

简单介绍了近年来关于宇宙微波背景辐射在观测上取得的重大进展，以及有关它的解释、理论和意义．宇宙微波背景是我们了解宇宙奥秘的一个至关重要的窗口．在未来几年，它还将扮演更加重要的角色．     

Cosmic Strings Coupled with a Massless Scalar Field

A scalar field generalization of Xanthopoulos's cylindrically symmetric solutions of the vacuum-Einstein equations is obtained. The obtained solution preserves the properties of the Xanthopoulos solution, which are regular on the axis, asymptotically flat, and free from the curvature singularities. The solution describes a stable, rotating cosmic string of infinite length interacting with gravitational and scalar waves.     

宇宙质心参考系

根据实际天文观测论述了膨胀着的宇宙系统的时间可以与空间分开来讨论;宇宙的空间是平直的。在宇宙质心坐标系中,由背景辐射温度、宇宙密度和宇宙半径（最远星系的距离）3个观测数据计算了宇宙这个引力系统的总能量,结果表明系统是一个引力束缚态,将来会收缩。在均匀分布的初始条件下计算了收缩过程,这是同步自由落体过程。在宇宙的膨胀过程与其收缩过程对称的假设之下,建立膨胀时间与背景辐射温度的一对一的对应关系。According to astronomical observation we point out that the time of our expanding cosmic system can be discussed separating from the space. And the space in our universe is flat. In the cosmic center-of-mass frame（CCF）, based on the temperature of CMBR, the cosmic density and the cosmic radii, the distance of the farmost galaxy, the total energy of our universe asa gravitation system has been calculated. It shows that our universe is in a gravitational bound state, and it will contract. In CCF the contracting progress is a synchronized freely falling body under initial condition of uniform distribution. Uder assumption of the symmetry of cosmic expanding and contracting progresses, th one-to-one correspondence of the expanding time to the temperature of CMBR can be obtained.     

Cosmic inflation from broken conformal symmetry

A period of rapidly accelerating expansion is expected in the early Universe implemented by a scalar field slowly rolling down along an asymptotically flat potential preferred by the current data. In this paper, we point out that this picture of the cosmic inflation with an asymptotically flat potential could emerge from the Palatini quadratic gravity by adding the matter field in such a way to break the local gauged conformal symmetry in both kinetic and potential terms.     

普朗克卫星：揭开宇宙深层次的秘密

文章对宇宙微波背景辐射这一学科做了简单的介绍,并根据普朗克卫星2015年的主要宇宙学结果,重点阐述了测定宇宙学参数、测量引力透镜、测量B-模式极化及其与南极BICEP实验的关系、检验宇宙暴胀模型、检测暗能量模型,以及寻找“丢失的重子物质”等问题,并对观测宇宙学未来的发展进行了展望。     

斯塔罗宾斯基与暴胀宇宙学

俄罗斯国家科学院院士阿里可塞·斯塔罗宾斯基(Alexei Starobinsky)教授是现代宇宙学暴胀模型的最早提出者之一,文中回顾了他在暴胀模型形成初期的具体贡献,并表达了他对暴胀模型和宇宙学未来发展的最新看法。     

A minimal gauge inflation model

In this paper, we present a gauge inflation model based on the orbifold M_4×S~1/Z_2 with non-Abelian SU(2) gauge symmetry, which is probably the simplest model in this category. As the inflaton potential is fully radiatively generated exclusively by gauge self-interactions, the model is predictive; thus, it is protected by gauge symmetry itself, without the introduction of any additional matter fields or arbitrary interactions. We show that the model fully agrees with the recent cosmological observations within the controlled perturbative regime of gauge interactions, g4≤1/(2πRMP), with the compactification radius(10 ≤ RMP ≤ 100): the expected magnitude of the curvature perturbation power spectrum and the value of the corresponding spectral index are in perfect agreement with the recent observations. The model also predicts a large fraction of the gravitational waves, negligible nonGaussianity, and a sufficiently high reheating temperature.     

Exploring the potentiality of future standard candles and standard sirens to detect cosmic opacity

In this work, we explore the potentiality of future gravitational wave (GW) and Type Ia supernovae (SNe Ia) measurements to detect cosmic opacity by comparing the opacity-free luminosity distance (LD) of GW events with the opacity-dependent LD of SNe Ia observations. The GW data are simulated from the future measurements of the ground-based Einstein Telescope (ET) and the space-borne Deci-Herz Interferometer Gravitational wave Observatory (DECIGO). The SNe Ia data are simulated from the observations of the Wide Field Infrared Survey Telescope (WFIRST) that will be collected over the next few decades. A binning method is adopted to match the GW data with the SNe Ia data at the same redshift z with a selection criterion \begin{document}$ |\Delta z|<0.005$\end{document}, and most of the available data from the GW measurements is employed to detect cosmic opacity due to improvements in the distribution of the future SNe Ia observations. Results show that the uncertainties of the constraints on cosmic opacity can be reduced to \begin{document}$ \sigma_{\epsilon}\sim 0.0041$\end{document} and 0.0014 at the \begin{document}$ 1\sigma$\end{document} confidence level (CL) for 1000 data points from the ET and DECIGO measurements, respectively. Compared with the allowable limits of intergalactic opacity obtained from quasar continuum observations, these future astronomical observations can be used to verify the cosmic opacity. In this way, GW and SNe Ia measurements can be used as important and effective tools to detect cosmic opacity in the future.     

Search for Sub-Solar Mass Binaries with Einstein Telescope and Cosmic Explorer

A possible detection of sub-solar mass ultra-compact objects would lead to new perspectives on the existence of black holes that are not of astrophysical origin and/or pertain to formation scenarios of exotic ultra-compact objects. Both possibilities open new perspectives for better understanding of our universe. In this work, we investigate the significance of detection of sub-solar mass binaries with components mass in the range: 10−2M⊙ up to 1M⊙, within the expected sensitivity of the ground-based gravitational waves detectors of third generation, viz., the Einstein Telescope (ET) and the Cosmic Explorer (CE). Assuming a minimum of amplitude signal-to-noise ratio for detection, viz., ρ=8, we find that the maximum horizon distances for an ultra-compact binary system with components mass 10−2M⊙ and 1M⊙ are 40 Mpc and 1.89 Gpc, respectively, for ET, and 125 Mpc and 5.8 Gpc, respectively, for CE. Other cases are also presented in the text. We derive the merger rate and discuss consequences on the abundances of primordial black hole (PBH), fPBH. Considering the entire mass range [10−2–1]M⊙, we find fPBH<0.70 (<0.06) for ET (CE), respectively.     

Spinors, Inflation, and Non-Singular Cyclic Cosmologies

We consider toy cosmological models in which a classical, homogeneous, spinor field provides a dominant or sub-dominant contribution to the energy-momentum tensor of a flat Friedmann-Robertson-Walker universe. We find that, if such a field were to exist, appropriate choices of the spinor self-interaction would generate a rich variety of behaviors, quite different from their widely studied scalar field counterparts. We first discuss solutions that incorporate a stage of cosmic inflation and estimate the primordial spectrum of density perturbations seeded during such a stage. Inflation driven by a spinor field turns out to be unappealing as it leads to a blue spectrum of perturbations and requires considerable fine-tuning of parameters. We next find that, for simple, quartic spinor self-interactions, non-singular cyclic cosmologies exist with reasonable parameter choices. These solutions might eventually be incorporated into a successful past- and future-eternal cosmological model free of singularities. In an Appendix, we discuss the classical treatment of spinors and argue that certain quantum systems might be approximated in terms of such fields.     

Cosmic no-hair conjecture in scalar-tensor theories

We have shown that, within the context of scalar-tensor theories, the anisotropic Bianchi-type cosmological models evolve towards de Sitter Universe. A similar result holds in the case of cosmology in Lyra manifold. Thus the analogue of cosmic no-hair theorem of Wald [1] hold in both the cases. In fact, during inflation there is no difference between scalar-tensor theories, Lyra’s manifold and general relativity (GR).     

小型宇宙射线探测仪的模拟和测量

介绍了一款小型宇宙射线探测仪。该仪器具有宇宙射线科普演示功能,主要用于实时测量μ子射线并显示计数,以及长时间尺度下（年）稳定地对不同角度的次级宇宙线通量进行监控记录。简要地展示了探测器的硬件构造和探测效率的模拟计算。探测仪单个探测器的探测效率为93.1%,两个探测器符合测量的探测效率为86.6%。根据探测器的计数率以及模拟计算的探测效率,估计了次级宇宙射线垂直地面方向的通量,为J=29±3 m-2 sr-1 s-1。另外,利用该宇宙射线探测仪,测量了兰州市区的次级宇宙射线的天顶角分布。其结果很好地满足I（θ）=IH+I₀ cosα θ经验公式,其中的角度依赖参数α=2.42±0.52。A small cosmic ray device is introduced in this paper.It has the demonstration function for popularization of science,and can be used mainly to display the μ counts in a real-time measurement,and to monitor the secondary cosmic ray flux at different angles in a very long time scale (years).We briefly show the hardware of the device and the detecting efficiency calculation by simulation.The detecting efficiency for one detector of the device is 93.1%,and the detecting efficiency is 86.6% for the coincidence measurement of two detectors.Based on the count rate by the detector and the simulated efficiency,the secondary cosmic ray flux perpendicular to the ground surface is measured,which is J=29±3 m-2sr-1 s-1.Moreover,with an application of the device,we measured the angular distribution of the secondary cosmic ray rate in Lanzhou City.The resulting angular distribution agrees well with the empirical formula as I(θ)=IH+I₀ cosα θ,in which the parameter for the angle-dependence is α=2.42±0.53.