Generalized second law of thermodynamics for FRW cosmology with power-law entropy correction

In this work, we have considered the power-law correction of entropy on the horizon. If the flat FRW Universe is filled with the n components fluid with interactions, the GSL of thermodynamics for apparent and event horizons have been investigated for equilibrium and non-equilibrium cases. If we consider a small perturbation around the de Sitter spacetime, the general conditions of the validity of GSL have been found. Also if a phantom dominated Universe has a pole-like type scale factor, the validity of GSL has also been analyzed. Further we have obtained constraints on the power-law parameter α in the phantom and quintessence dominated regimes. Finally we obtain conditions under which GSL breaks down in a cosmological background.     

Role of Brans-Dicke Theory with?or?without?Self-Interacting Potential in?Cosmic?Acceleration

In this work we have studied the possibility of obtaining cosmic acceleration in Brans-Dicke theory with varying or constant ω (Brans-Dicke parameter) and with or without self-interacting potential, the background fluid being barotropic fluid or Generalized Chaplygin Gas. Here we take the power law form of the scale factor and the scalar field. We show that accelerated expansion can also be achieved for high values of ω for closed Universe.     

Geometric sigma model of the Universe

The purpose of this work is to demonstrate how an arbitrarily chosen background of the Universe can be made a solution of a simple geometric sigma model.Geometric sigma models are purely geometric theories in which spacetime coordinates are seen as scalar fields coupled to gravity.Although they look like ordinary sigma models,they have the peculiarity that their complete matter content can be gauged away.The remaining geometric theory possesses a background solution that is predefined in the process of constructing the theory.The fact that background configuration is specified in advance is another peculiarity of geometric sigma models.In this paper,I construct geometric sigma models based on different background geometries of the Universe.Whatever background geometry is chosen,the dynamics of its small perturbations is shown to have a generic classical stability.This way,any freely chosen background metric is made a stable solution of a simple model.Three particular models of the Universe are considered as examples of how this is done in practice.     

Spacetime emergence of the robertson-walker universe from a matrix model

Using a novel, string theory-inspired formalism based on a Hamiltonian constraint, we obtain a conformal mechanical system for the spatially flat four-dimensional Robertson-Walker Universe. Depending on parameter choices, this system describes either a relativistic particle in the Robertson-Walker background or metric fluctuations of the Robertson-Walker geometry. Moreover, we derive a tree-level M theory matrix model in this time-dependent background. Imposing the Hamiltonian constraint forces the spacetime geometry to be fuzzy near the big bang, while the classical Robertson-Walker geometry emerges as the Universe expands. From our approach, we also derive the temperature of the Universe interpolating between the radiation and matter dominated eras.     

Non-equilibrium in cosmology

All the non-trivial features of the Universe we see around us, such as particles, stars, galaxies, and clusters of galaxies, are the result of non-equilibrium processes in the cosmic evolution. These lectures aim to provide some general background in cosmology and to examine specific, and notable, examples of departures from thermal equilibrium. They are organized as follows: 1) Overview of the thermal history of the Universe after the Big Bang: the relevant time-scales and the mechanism of particle decoupling from the themal bath; 2) Explicit examples of cosmic relics: nucleosynthesis, photons and the cosmic microwave background, neutrinos, and cold dark matter; 3) Baryogenesis: the generation of the baryon asymmetry of the Universe; 4) The formation of cosmic structures (galaxies, clusters of galaxies): from the Vlasov equation to the renormalization group.     

Evidence for the quantum birth of our universe

We present evidence for a nonsingular origin of the Universe with intial conditions determined by quantum physics and relativistic gravity. In particular, we establish that the present temperature of the microwave background and the present density of the Universe agree well with our predictions from these intial conditions, after evolution to the present age using the Einstein-Friedmann equation. Remarkably, the quantum origin for the Universe naturally allows its evolution at exactly the critical density. We also discuss the consequences of these results to some fundamental aspects of quantum physics in the early Universe.     

Some exact solutions of magnetized viscous model in string cosmology

In this paper, we study anisotropic Bianchi-V Universe with magnetic field and bulk viscous fluid in string cosmology. Exact solutions of the field equations are obtained by using the equation of state (EoS) for a cloud of strings, and a relationship between bulk viscous coefficient and scalar expansion. The bulk viscous coefficient is assumed to be inversely proportional to the expansion scalar. It is interesting to examine the effects of magnetized bulk viscous string model in early and late stages of evolution of the Universe. This paper presents different string models like geometrical (Nambu string), Takabayasi (p-string) and Reddy string models by taking certain physical conditions. We discuss the nature of classical potential for viscous fluid with and without magnetic field. The presence of bulk viscosity stops the Universe from becoming empty in its future evolution. It is observed that the Universe expands with decelerated rate in the presence of viscous fluid with magnetic field whereas, it expands with marginal inflation in the presence of viscous fluid without magnetic field. The other physical and geometrical aspects of each string model are discussed in detail.     

New constraints on neutrino physics from BOOMERANG data

We have performed a likelihood analysis of the recent data on the cosmic microwave background radiation anisotropy from the BOOMERANG experiment. These data place a strong upper bound on the radiation density present at recombination. Expressed in terms of the equivalent number of neutrino species the 2sigma bound is N(nu)相似文献   

Influence of structural and doping parameter variations on Si and $$\hbox {Si}_{1-x}$$$$\hbox {Ge}_{x}$$Gex double gate tunnel FETs: An analysis for RF performance enhancement

In this paper, we propose a stochastic evolution of the early Universe which can lead to a fractal correlation in galactic distribution in the Universe. The stochastic equation of state, due to fluctuating creation rates of various components in a many-component fluid, leads to a fluctuating expansion rate for the Universe in the early epochs. It provides persistent fluctuations in the number count vs. apparent magnitude relation, as expected from the observation of a fractal distribution of the galaxies. We also present a stochastic evolution of density perturbations in the early Universe.     

Detecting relics of a thermal gravitational wave background in the early Universe

A thermal gravitational wave background can be produced in the early Universe if a radiation dominated epoch precedes the usual inflationary stage. This background provides a unique way to study the initial state of the Universe. We discuss the imprint of this thermal spectra of gravitons on the cosmic microwave background (CMB) power spectra, and its possible detection by CMB observations. Assuming the inflationary stage is a pure de Sitter expansion we find that, if the number of e-folds of inflation is smaller than 65, the signal of this thermal spectrum can be detected by the observations of Planck and PolarBear experiments, or the planned EPIC experiments. This bound can be even looser if inflation-like stage is the sub-exponential.     

Early inflation,isotropization, and late time acceleration in a Bianchi type-I universe

A system of Einstein equations is solved for the Bianchi type-I metrics that describes a homogeneous and isotropic Universe. The system contains nonlinear differential equations of the second-order, which depend only on time. The method of solution is described, and the general form of the solution is found. Explicit analytical expressions are obtained in some particular cases. Numerical integration is used to describe possible solution types in the general case. The evolution of the Universe has been investigated in the presence of different types of sources, namely, a perfect fluid, a van der Waals fluid, the cosmological constant, quintessence, a Chaplygin gas, a modified quintessence, and a nonlinear spinor field. It is shown that the presence of a van der Waals fluid leads to inflation in the early stage of evolution, while the modified quintessence leads to a cyclic or oscillating Universe. It has been shown, that for some special choice of parameters the late time acceleration can be attributed to the influence of a nonlinear spinor field.     

Letter: Brane Cosmology with a van der Waals Equation of State

The evolution of a Universe confined onto a 3-brane embedded in a five-dimensional space-time is investigated where the cosmological fluid on the brane is modeled by the van der Waals equation of state. It is shown that the Universe on the brane evolves in such a manner that three distinct periods concerning its acceleration field are attained: (a) an initial accelerated epoch where the van der Waals fluid behaves like a scalar field with a negative pressure; (b) a past decelerated period which has two contributions, one of them is related to the van der Waals fluid which behaves like a matter field with a positive pressure, whereas the other contribution comes from a term of the Friedmann equation on the brane which is inversely proportional to the scale factor to the fourth power and can be interpreted as a radiation field, and (c) a present accelerated phase due to a cosmological constant on the brane.     

Scientific discovery with the James Webb Space Telescope

For the past 400 years, astronomers have sought to observe and interpret the Universe by building more powerful telescopes. These incredible instruments extend the capabilities of one of our most important senses, sight, towards new limits such as increased sensitivity and resolution, new dimensions such as exploration of wavelengths across the full electromagnetic spectrum, new information content such as analysis through spectroscopy, and new cadences such as rapid time-series views of the variable sky. The results from these investments, from small to large telescopes on the ground and in space, have completely transformed our understanding of the Universe; including the discovery that Earth is not the centre of the Universe, that the Milky Way is one among many galaxies in the Universe, that relic cosmic background radiation fills all space in the early Universe, that that the expansion rate of the Universe is accelerating, that exoplanets are common around stars, that gravitational waves exist, and much more. For modern astronomical research, the next wave of breakthroughs in fields ranging over planetary, stellar, galactic, and extragalactic science motivate a general-purpose observatory that is optimised at near- and mid-infrared wavelengths, and that has much greater sensitivity, resolution, and spectroscopic multiplexing than all previous telescopes. This scientific vision, from measuring the composition of rocky worlds in the nearby Milky Way galaxy to finding the first sources of light in the Universe to other topics at the forefront of modern astrophysics, motivates the state-of-the-art James Webb Space Telescope (Webb). In this review paper, I summarise the design and technical capabilities of Webb and the scientific opportunities that it enables.     

The gravitational wave symphony of the Universe

The new millennium will see the upcoming of several ground-based interferometric gravitational wave antennas. Within the next decade a space-based antenna may also begin to observe the distant Universe. These gravitational wave detectors will together operate as a network taking data continuously for several years, watching the transient and continuous phenomena occurring in the deep cores of astronomical objects and dense environs of the early Universe where gravity was extremely strong and highly nonlinear. The network will listen to the waves from rapidly spinning non-axisymmetric neutron stars, normal modes of black holes, binary black hole inspiral and merger, phase transitions in the early Universe, quantum fluctuations resulting in a characteristic background in the early Universe. The gravitational wave antennas will open a new window to observe the dark Universe unreachable via other channels of astronomical observations.     

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．     

Review of dark matter direct detection experiments

Matter, as we know it, makes up less than 5% of the Universe. Various astrophysical observations have confirmed that one quarter of the Universe and most of the matter content in the Universe is made up of dark matter. The nature of dark matter is yet to be discovered and is one of the biggest questions in physics. Particle physics combined with astrophysical measurements of the abundance gives rise to a dark matter candidate called weakly interacting massive particle (WIMP). The low density of WIMPs in the galaxies and the extremely weak nature of the interaction with ordinary matter make detection of the WIMP an extraordinarily challenging task, with abundant fakes from various radioactive and cosmogenic backgrounds with much stronger electromagnetic interaction. The extremely weak nature of the WIMP interaction dictates detectors that have extremely low naturally occurring radioactive background, a large active volume (mass) of sensitive detector material to maximize statistics, a highly efficient detector-based rejection mechanism for the dominant electromagnetic background and sophisticated analysis techniques to reject any residual background. This paper reviews currently available major technologies being pursued by various collaborations, with special emphasis on the cryogenic Ge detector technology used by the Cryogenic Dark Matter Search Collaboration (CDMS).     

Stochastic background of gravitational waves from hybrid preheating

The process of reheating the Universe after hybrid inflation is extremely violent. It proceeds through the nucleation and subsequent collision of large concentrations of energy density in bubblelike structures, which generate a significant fraction of energy in the form of gravitational waves. We study the power spectrum of the stochastic background of gravitational waves produced at reheating after hybrid inflation. We find that the amplitude could be significant for high-scale models, although the typical frequencies are well beyond what could be reached by planned gravitational wave observatories. On the other hand, low-scale models could still produce a detectable stochastic background at frequencies accessible to those detectors. The discovery of such a background would open a new window into the very early Universe.