13 research outputs found
A Godel-Friedman cosmology?
Based on the mathematical similarity between the Friedman open metric and
Godel's metric in the case of nearby distances, we investigate a new scenario
for the Universe's evolution, where the present Friedman universe originates
from a primordial Godel universe by a phase transition during which the
cosmological constant vanishes. Using Hubble's constant and the present matter
density as input, we show that the radius and density of the primordial Godel
universe are close, in order of magnitude, to the present values, and that the
time of expansion coincides with the age of the Universe in the standard
Friedman model. In addition, the conservation of angular momentum provides, in
this context, a possible origin for the rotation of galaxies, leading to a
relation between the masses and spins corroborated by observational data.Comment: Extended version, accepted for publication in Physical Review
A General Relativistic Model for Magnetic Monopole-Infused Compact Objects
Emergent concepts from astroparticle physics are incorporated into a
classical solution of the Einstein-Maxwell equations for a binary
magnetohydrodynamic fluid, in order to describe the final equilibrium state of
compact objects infused with magnetic monopoles produced by proton-proton
collisions within the intense dipolar magnetic fields generated by these
objects during their collapse. It is found that the effective mass of such an
object's acquired monopolar magnetic field is three times greater than the mass
of its native fluid and monopoles combined, necessitating that the interior
matter undergo a transition to a state of negative pressure in order to attain
equilibrium. Assuming full symmetry between the electric and magnetic Maxwell
equations yields expressions for the monopole charge density and magnetic field
by direct analogy with their electrostatic equivalents; inserting these into
the Einstein equations then leads to an interior metric which is well-behaved
from the origin to the surface, where it matches smoothly to an exterior
magnetic Reissner-Nordstr\"om metric free of any coordinate pathologies. The
source fields comprising the model are all described by simple, well-behaved
polynomial functions of the radial coordinate, and are combined with
straightforward regularity conditions to yield expressions delimiting several
fundamental physical parameters pertaining to this hypothetical astrophysical
object.Comment: Accepted for publication in "Astrophysics and Space Science.
Thermodynamic Properties of the Dimerised and Frustrated S=1/2 Chain
By high temperature series expansion, exact diagonalisation and temperature
density-matrix renormalisation the magnetic susceptibility and the
specific heat of dimerised and frustrated chains are computed.
All three methods yield reliable results, in particular for not too small
temperatures or not too small gaps. The series expansion results are provided
in the form of polynomials allowing very fast and convenient fits in data
analysis using algebraic programmes. We discuss the difficulty to extract more
than two coupling constants from the temperature dependence of .Comment: 14 pages, 13 figures, 4 table
Thermodynamic properties of the two-dimensional S=1/2 Heisenberg antiferromagnet coupled to bond phonons
By applying a quantum Monte Carlo procedure based on the loop algorithm we
investigate thermodynamic properties of the two-dimensional antiferromagnetic
S=1/2 Heisenberg model coupled to Einstein phonons on the bonds. The
temperature dependence of the magnetic susceptibility, mean phonon occupation
numbers and the specific heat are discussed in detail. We study the spin
correlation function both in the regime of weak and strong spin phonon coupling
(coupling constants g=0.1, w=8J and g=2, w=2J, respectively). A finite size
scaling analysis of the correlation length indicates that in both cases long
range Neel order is established in the ground state.Comment: 10 pages, 13 figure