Essay: Preheating and Turbulence: Echoes of a Not So Quiet Universe

We study the nonlinear decay of the inflaton which causes the reheating of the Universe in the transition from the inflationary phase to the radiation dominated phase, resulting in the creation of almost all matter constituting the present Universe. Our treatment allows us to follow the full dynamics of the system in a long time regime, and to describe not only the parametric resonance processes with nonlinear restructuring but also to characterize a final turbulent state in the dynamics by which the energy is nonlinearly transferred to all scales of the system with a consequent thermalization of the created matter.     

Entropy of the Universe and Standard Cosmology

By means of a variant approach to Standard Relativistic Cosmology, we hint that the entropy of the Universe is growing with t ^3/2, where t stands for time-coordinate. Then, the absolute temperature obeys Standard t ^−1/2-dependence. We make contact with our previous paper (Berman, Int. J. Theor. Phys., 2009), in the context of a Machian Universe; but we also consider the dependencies of the scale-factor and energy density, with time, as in Standard treatments.     

Entropy of the Universe

After a discussion on several limiting cases where General Relativity turns into less sophisticated theories, we find that in the correct thermodynamical and cosmological weak field limit of Einstein’s field equations the entropy of the Universe is R ^3/2-dependent, where R stands for the radius of the causally related Universe. Thus, entropy grows in the Universe, contrary to Standard Cosmology prediction.     

Massless particles and cosmology

Post recombination density perturbations have been studied in a two-component matter-radiation universe. The study has been carried out for variable matter and radiation densities. The possibility of the existence of different kinds of neutrinos in addition to the electronic, muonic and taonic has been considered and conclusions have been drawn as to the upper limit of the radiation density for different values of Ω _m .     

Why the Initial Infinite Singularity of the Universe Is Not There

We “explain”, using a Classical approach, how the Universe was created out of “nothing”, i.e., with no input of initial energy. This is a Universe with no-initial infinite singularity of energy density.     

Early Universe in Scalar-Tensor Theory

We consider the flat Robertson–Walker model in scalar-tensor theory proposed by Lau and Prokhovnik. In this model, the field equations are solved by using “gamma-law” form of equation of state p=(γ−1)ρ, where the adiabatic parameter ‘gamma’ (γ) varies continuously as the universe expands. Our aim is to study how the adiabatic parameter γ should vary so that in the course of its evolution the universe goes through a transition from an inflationary to a radiation-dominated phase. A unified one parameter function of γ has been considered to describe the two early phases of evolution of universe. The solutions show the power-law expansion and cosmological constant is found to be positive and decreasing function of cosmic time. The solutions are compatible with the Dirac’s large number hypothesis. The deceleration parameter has been presented in a unified manner in terms of scale factor, which describes the inflation of the model. The nature of singularity and the physical properties have been discussed in details.     

Causal dissipative cosmology

The full version of the causal thermodynamics of non-equilibrium phenomena is discussed in the context of the flat Friedmann-Robertson-Walker cosmological model. Power law solutions for the scale factor are shown to exist. It is also shown that the temporal behaviour of the temperature depends on the functional dependence of the coefficient of bulk viscosity on density.     

Summary of cosmology workshop

Cosmology is passing through a golden phase of rapid advance. The cosmology workshop at ICGC-2004 attracted a large number of research contributions to diverse topics of cosmology. I attempt to classify and summarize the research work and results of the oral and poster presentations made at the meeting.     

第六讲超弦理论与宇宙学的挑战

超弦理论从根本上改变了人们对时空的看法，时空在弦论中只是一种宏观体现．弦论中的非经典时空影响早期宇宙的发展，在一些观测宇宙学的实验中人们也许会发现弦论的效应，例如微波背景辐射的功率谱的反常．最近发现的暗能量也对弦论宇宙学提出了挑战．     

Accelerating cosmology in modified gravity with scalar field

The modified gravity with 1/R term (R being the scalar curvature) and the Einstein-Hilbert term is studied by incorporating the phantom scalar field. A number of cosmological solutions are derived in the presence of the phantom field in the perfect fluid background. It is shown: the current inflation obtained in the modified gravity is affected by the existence of the phantom field.     

The current status of observational cosmology

Observational cosmology has indeed made very rapid progress in recent years. The ability to quantify the universe has largely improved due to observational constraints coming from structure formation. The transition to precision cosmology has been spear-headed by measurements of the anisotropy in the cosmic microwave background (CMB) over the past decade. Observations of the large scale structure in the distribution of galaxies, high red-shift supernova, have provided the required complementary information. We review the current status of cosmological parameter estimates from joint analysis of CMB anisotropy and large scale structure (LSS) data. We also sound a note of caution on overstating the successes achieved thus far.     

Noncommutative quantum cosmology

We consider noncommutative quantum cosmology in the case of the low-energy string effective theory. Exact solutions are found and compared with the commutative case.     

Baryogenesis and the new cosmology

I begin this talk with a brief review of the status of approaches to understanding the origin of the baryon asymmetry of the Universe (BAU). I then describe a recent model unifying three seemingly distinct problems facing particle cosmology: the origin of inflation, the generation of the BAU and the nature of dark energy.     

Bianchi Type-II inflationary models with constant deceleration parameter in general relativity

Einstein’s field equations are considered for a locally rotationally symmetric Bianchi Type-II space-time in the presence of a massless scalar field with a scalar potential. Exact solutions of scale factors and other physical parameters are obtained by using a special law of variation for Hubble’s parameter that yields a constant value of deceleration parameter. To get inflationary solutions, a flat region is considered in which the scalar potential is constant. Power-law and exponential cases are studied and in both solutions there is an anisotropic expansion of the cosmic fluid, but the fluid has vanishing vorticity. A detailed study of geometrical and kinematical properties of solutions has been carried out.      

Machian Inertia and the Isotropic Universe

This paper addresses the origin of the forces of inertia. It proposes a Newton-Mach particle interaction force between all pairs of particles that depends on their relative acceleration and is proportional to the gravitational force between them. The motion of all objects therefore becomes directly influenced by all of the matter in the universe, as prescribed by Mach's principle. The effect of the observed hierarchical structure of the universe is considered and is used to ensure that the inertial force on an object is finite and isotropic. The instantaneous matter interaction force is justified and both Einstein's and Mach's objections to a Newtonian framework are discussed and shown to be absorbed by the proposed universal law of inertia.