12 research outputs found
Evolution of Primordial Black Holes in Loop Quantum Gravity
In this work, we study the evolution of Primordial Black Holes within the
context of Loop Quantum Gravity. First we calculate the scale factor and energy
density of the universe for different cosmic era and then taking these as
inputs we study evolution of primordial black holes. From our estimation it is
found that accretion of radiation does not affect evolution of primordial black
holes in loop quantum gravity even though a larger number of primordial black
holes may form in early universe in comparison with Einstein's or scalar-tensor
theories.Comment: 8 pages, 1 figur
Evolution of Primordial Black Hole Mass Spectrum in Brans-Dicke Theory
We investigate the evolution of primordial black hole mass spectrum by
including both accretion of radiation and Hawking evaporation within
Brans-Dicke cosmology in radiation, matter and vacuum-dominated eras. We also
consider the effect of evaporation of primordial black holes on the expansion
dynamics of the universe. The analytic solutions describing the energy density
of the black holes in equilibrium with radiation are presented. We demonstrate
that these solutions act as attractors for the system ensuring stability for
both linear and nonlinear situations. We show, however, that inclusion of
accretion of radiation delays the onset of this equilibrium in all radiation,
matter and vacuum-dominated eras.Comment: 18 pages, one figur
Study of attractive hard-core Yukawa fluids of variable range
845-849The
thermodynamic and structural properties of purely attractive hard-core Yukawa
particles in the fluid state are determined in the high-temperature expansion
of the mean spherical solution (MSA-HTE) to the Ornstein-Zernike equation. The
radial distribution function at contact of attractive hard-core Yukawa
particles is reported by introducing second order perturbation term, thus
improving its accuracy. Further, systems of particles with Yukawa screening
length λ = 1.8, 3.0 and 4.0 are examined and compared with the results obtained
by simulation
Scaling laws for transport coefficients of a hard sphere fluid
The analytical forms of the time correlation functions of the transport coefficients in Green-Kubo formulas have been analyzed to determine the dependence of the shear viscosity, longitudinal viscosity and thermal conductivity on the excess entropy for a hard sphere system. Thus the scaling laws between the transport coefficients and the excess entropy and between transport coefficients and equation of state are proposed. These analytical expressions of the transport coefficients give us the possibility to extend the investigation for the expressions of the chain molecules. © 2007
Transport coefficients of square-well fluids
We analyze the analytical form of the velocity time correlation function of a hard sphere system obtained by employing generalized Langevin equation for a square-well fluid. The self-diffusion coefficient and shear viscosity have been calculated using this analytical form of velocity tcf for a square-well fluid. The addition of an attractive square-well potential in place of hard sphere leads to a substantial influence on transport coefficients. Unlike harmonic model diffusion coefficient no longer vanishes. A breakdown of the Stokes–Einstein relation is observed at low densities for a square-well fluid
Cyclic and heteroclinic flows near general static spherically symmetric black holes
We investigate the Michel-type accretion onto a static spherically symmetric black hole. Using a Hamiltonian dynamical approach, we show that the standard method employed for tackling the accretion problem has masked some properties of the fluid flow. We determine new analytical solutions that are neither transonic nor supersonic as the fluid approaches the horizon(s); rather, they remain subsonic for all values of the radial coordinate. Moreover, the three-velocity vanishes and the pressure diverges on the horizon(s), resulting in a flow-out of the fluid under the effect of its own pressure. This is in favor of the earlier prediction that pressure-dominant regions form near the horizon. This result does not depend on the form of the metric and it applies to a neighborhood of any horizon where the time coordinate is timelike. For anti-de Sitter-like f(R) black holes we discuss the stability of the critical flow and determine separatrix heteroclinic orbits. For de Sitter-like f(R) black holes, we construct polytropic cyclic, non-homoclinic, physical flows connecting the two horizons. These flows become non-relativistic for Hamiltonian values higher than the critical value, allowing for a good estimate of the proper period of the flow