7 research outputs found
Conformal transformation in theories
It is well-known that theories are dynamically equivalent to a
particular class of scalar-tensor theories. In analogy to the extension
of the Einstein-Hilbert action of general relativity, theories are
generalizations of the action of teleparallel gravity. The field equations are
always second order, remarkably simpler than theories. It is interesting
to investigate whether theories have the similar conformal features
possessed in theories. It is shown, however, that theories are
not dynamically equivalent to teleparallel action plus a scalar field via
conformal transformation, there appears an additional scalar-torsion coupling
term. We discuss briefly what constraint of this coupling term may be put on
theories from observations of the solar system.Comment: 4 pages, Revision to be publishe
Analysis of scalar perturbations in cosmological models with a non-local scalar field
We develop the cosmological perturbations formalism in models with a single
non-local scalar field originating from the string field theory description of
the rolling tachyon dynamics. We construct the equation for the energy density
perturbations of the non-local scalar field in the presence of the arbitrary
potential and formulate the local system of equations for perturbations in the
linearized model when both simple and double roots of the characteristic
equation are present. We carry out the general analysis related to the
curvature and entropy perturbations and consider the most specific example of
perturbations when important quantities in the model become complex.Comment: LaTeX, 25 pages, 1 figure, v2: Subsection 3.2 and Section 5 added,
references added, accepted for publication in Class. Quant. Grav. arXiv admin
note: text overlap with arXiv:0903.517
Notes on interacting holographic dark energy model in a closed universe
We consider interacting holographic dark energy model in Friedmann Robertson
Walker space time with positive spatial curvature and investigate the behavior
of curvature parameter and dark energy density in accelerated expanding epoch.
We also derive some conditions needed to cross the phantom divide line in this
model.Comment: 10 pages, typos corrected, some explanations and references added and
updated, accepted for publication in JCA