Inheriting Conformal and Special Conformal Killing Vectors in String Cosmology

In this paper we study the consequences of the existence of conformal and special conformal Killing vectors (CKV, SCKV) for string cloud and string fluid in the context of general relativity. The inheritance symmetries of the string cloud and string fluid are discussed. Einstein's field equations have been solved for static spherically symmetric space-time with cloud and fluid of strings source via CKV.     

A Self-Similar Dynamics in Viscous Spheres

We study the evolution of radiating and viscous fluid spheres assuming an additional homothetic symmetry on the spherically symmetric space-time. We match a very simple solution to the symmetry equations with the exterior one (Vaidya). We then obtain a system of two ordinary differential equations which rule the dynamics, and find a self-similar collapse which is shear-free and with a barotropic equation of state. Considering a huge set of initial self-similar dynamics states, we work out a model with an acceptable physical behavior.     

Particle Creation in Anisotropically Expanding Universe

Using squeezed vacuum states formalism of quantum optics, a homogeneous and massive scalar field minimally coupled to gravity in Bianchi type-I model of the universe is examined in the frame work of semiclassical theory of gravity. Hence an approximate leading solution to the semiclassical Einstein equation is found. The next order solution for each scale factor in their respective direction show power law of expansion. It is further noted that evolution of scale factors are mutually correlated. The phenomena of nonclassical particle creation is also examined in the anisotropic background cosmology.     

Spin 2 Field Equation in Expanding Universe

The spin 2 field equations are separated in the Robertson-Walker space-time by the Newman-Penrose formalism and by using a null tetrad frame previously considered. The angular and radial separated equations are integrated by generalizing and improving results relative to the massless case. The separated time equations are governed by two coupled linear differential equations that depend on the cosmological background. They are solved and studied for some models of cosmological expansion such as the linear and exponential expansion and the matter dominated and radiative expansion of the standard cosmology.     

Self-Attracting Poisson Clouds in an Expanding Universe

 We consider the following elementary model for clustering by ballistic aggregation in an expanding universe. At the initial time, there is a doubly infinite sequence of particles lying in a one-dimensional universe that is expanding at constant rate. We suppose that each particle p attracts points at a certain rate a(p)/2 depending only on p, and when two particles, say p and q, collide by the effect of attraction, they merge as a single particle p*q. The main purpose of this work is to point at the following remarkable property of Poisson clouds in these dynamics. Under certain technical conditions, if at the initial time the system is distributed according to a spatially stationary Poisson cloud with intensity μ ₀ , then at any time t > 0, the system will again have a Poissonian distribution, now with intensity μ _t , where the family solves a generalization of Smoluchowski's coagulation equation. Received: 15 February 2002 / Accepted: 8 July 2002 Published online: 7 November 2002     

The Evolution for Various Matter Perturbations in the Expanding Universe

We present a systematic treatment of the linear theory of scalar gravitational perturbations of various matter (including baryons, cold dark matter, photons, massless neutrinos,and massive neutrino) for the flat, open and close universes, concentrating on the treatment of the massive neutrino component which has been either ignored or approximated crudely for the nonflat universe in previous literatures.     

Inequivalence of Jordan and Einstein Frame: What Is the Low Energy Gravity in String Theory?

It is well-known that any scalar can be promoted to a Jordan-Brans-Dicke type scalar coupling to the Einstein-Hilbert term through a field dependent Weyl transformation of the metric. The Weyl rescaling also transforms mass terms into coupling constants between matter and the scalar. It is pointed out that there exists a distinguished metric where all scalars decouple from an arbitrary fiducial fermion, e.g. the nucleon. If bound states of this fermion are used to define distances and to probe the interior of the forward light cone, it seems reasonable to say that the metric in that particular frame defines the local geometry of space-time at low energies, as probed by experimental gravity and cosmology.     

Dynamics of Temperature Distribution of Gravitationally Bound Objects in the Expanding Universe

Physics of Atomic Nuclei - In this article, we consider a cluster of primordial black holes (PHBs) which decoupled from the cosmic expansion. A characteristic feature of the formed region is an...     

Dark Energy Accretion onto a Black Hole in an Expanding Universe

By using the solution describing a black hole embedded in the FLRW universe, we obtain the evolving equation of the black hole mass expressed in terms of the cosmological parameters. The evolving equation indicates that in the phantom dark energy universe the black hole mass becomes zero before the Big Rip is reached.     

Thermodynamic Parameters of the Gauche-Trans Equilibrium in Ethylene Glycol

The Raman spectrum of ethylene glycol was studied as a function of temperature in the neat liquid and at two concentrations in the solvent, DMSO. Relative intensities of the gauche C-C-O bending mode and the C-C stretch (coincident for both rotamers) were utilized to calculate δH and TδS for each of the mixtures. It was observed that dilution in the solvent stabilizes the trans conformer, whereas variation in the entropy difference appears to favor the gauche form.     

Pre-relaxation Processes in a Radiating Relativistic Sphere

The influence of processes occurring before the system relaxes into diffusion, on the evolution of a radiating sphere, is exhibited in a specific example. The luminosity profiles, and consequently the general evolution of the object, are shown to be quite sensitive to the value of relaxation time.     

The Dynamical Instability of Static, Spherically Symmetric Solutions in Nonsymmetric Gravitational Theories

We consider the dynamical stability of a class of static, spherically symmetric solutions of the nonsymmetric gravitational theory. We numerically reproduce the Wyman solution and generate new solutions for the case where the theory has a nontrivial fundamental length scale ^-1. By considering spherically symmetric perturbations of these solutions we show that the Wyman solutions are generically unstable.     

String Thermalization in Static Spacetimes

We study the evolution, the transverse spreadingand the subsequent thermalization of string states inthe Weyl static axisymmetric spacetime. This possessesa singular event horizon on the symmetry axis and a naked singularity along the otherdirections. The branching diffusion process of stringbits approaching the singular black-hole horizonprovides the notion of the temperature that iscalculated for this process. We find that the solution of theFokker-Planck equation in the phase space of thetransverse variables of the string, can be factored asa product of two thermal distributions, provided that the classical conjugate variables satisfy theuncertainty principle. We comment on the possiblephysical significance of this result.     

Disquisitions Relating to Principles of Thermodynamic Equilibrium in Climate Modelling

We revisit the fundamental principles of thermodynamic equilibrium in relation to heat transfer processes within the Earth’s atmosphere. A knowledge of equilibrium states at ambient temperatures (T) and pressures (p) and deviations for these p-T states due to various transport ‘forces’ and flux events give rise to gradients (dT/dz) and (dp/dz) of height z throughout the atmosphere. Fluctuations about these troposphere averages determine weather and climates. Concentric and time-span average values <T> (z, Δt)) and its gradients known as the lapse rate = d < T(z) >/dz have hitherto been assumed in climate models to be determined by a closed, reversible, and adiabatic expansion process against the constant gravitational force of acceleration (g). Thermodynamics tells us nothing about the process mechanisms, but adiabatic-expansion hypothesis is deemed in climate computer models to be convection rather than conduction or radiation. This prevailing climate modelling hypothesis violates the 2nd law of thermodynamics. This idealized hypothetical process cannot be the causal explanation of the experimentally observed mean lapse rate (approx.−6.5 K/km) in the troposphere. Rather, the troposphere lapse rate is primarily determined by the radiation heat-transfer processes between black-body or IR emissivity and IR and sunlight absorption. When the effect of transducer gases (H₂O and CO₂) is added to the Earth’s emission radiation balance in a 1D-2level primitive model, a linear lapse rate is obtained. This rigorous result for a perturbing cooling effect of transducer (‘greenhouse’) gases on an otherwise sunlight-transducer gas-free troposphere has profound implications. One corollary is the conclusion that increasing the concentration of an existing weak transducer, i.e., CO₂, could only have a net cooling effect, if any, on the concentric average <T> (z = 0) at sea level and lower troposphere (z < 1 km). A more plausible explanation of global warming is the enthalpy emission ’footprint’ of all fuels, including nuclear.