45 research outputs found
Quintessence and Gravitational Waves
We investigate some aspects of quintessence models with a non-minimally
coupled scalar field and in particular we show that it can behave as a
component of matter with . We study the
properties of gravitational waves in this class of models and discuss their
energy spectrum and the cosmic microwave background anisotropies they induce.
We also show that gravitational waves are damped by the anisotropic stress of
the radiation and that their energy spectrum may help to distinguish between
inverse power law potential and supergravity motivated potential. We finish by
a discussion on the constraints arising from their density parameter
\Omega_\GW.Comment: 21 pages, 18 figures, fianl version, accepted for publication in PR
Holographic Dark Energy in Brans-Dicke Theory
In this paper, the holographic dark energy model is considered in Brans-Dicke
theory where the holographic dark energy density is replaced with . Here
is a time variable Newton constant. With this
replacement, it is found that no accelerated expansion universe will be
achieved when the Hubble horizon is taken as the role of IR cut-off. When the
event horizon is adopted as the IR cut-off, an accelerated expansion universe
is obtained. In this case, the equation of state of holographic dark energy
takes a modified form
. In the limit , the 'standard' holographic dark energy is recovered. In the holographic
dark energy dominated epoch, power-law and de Sitter time-space solutions are
obtained.Comment: 7 pages, 1 figure, match the published versio
Tracking Extended Quintessence
We study the cosmological role of a Tracking Field in Extended
Quintessence scenarios (TEQ), where the dynamical vacuum energy driving the
acceleration of the universe today is coupled with the Ricci scalar, , with
a term of the form , where . Tracker solutions for these NMC models, with
inverse power-law potentials, possess an initial enhancement of the scalar
field dynamics, named -boost, caused by the Ricci scalar in the Klein-Gordon
equation. During this phase the field performs a "gravitational" slow rolling
which we model analytically, with energy density scaling as . We
evolve linear perturbations in TEQ models assuming Gaussian scale-invariant
initial spectrum. We obtain significant changes in the Integrated Sachs Wolfe
effect and in the acoustic peaks locations on the Cosmic Microwave Background,
as well as in the turnover on the matter power spectrum. All these corrections
may assume positive as well as negative values, depending on the sign of the
NMC parameter . We give analytical formulas describing all these effects.
We show that they can be as large as with respect to equivalent
cosmological constant and ordinary tracking Quintessence models, respecting all
the existing experimental constraints on scalar-tensor theories of gravity.
These results demonstrate that the next decade data will provide deep
constraints on the nature of the dark energy in the Universe, as well as the
structure of the theory of gravity.Comment: 24 pages including 8 figures, final version to be published in
Phys.Rev.
Domestic Violence and Health Care: Opening Pandora¿s Box ¿ Challenges and Dilemmas
In this article we take a critical stance toward the rational progressive narrative
surrounding the integration of domestic violence within health care. Whilst changes in
recent UK policy and practice have resulted in several tangible benefits, it is argued that
there may be hidden dilemmas and challenges. We suggest that the medical model of care
and its discursive practices position women as individually accountable for domestic
violence-related symptoms and injuries. This may not only be ineffective in terms of
service provision but could also have the potential to reduce the political significance of
domestic violence as an issue of concern for all women. Furthermore, it is argued that the
use of specific metaphors enables practitioners to distance themselves from interactions
that may prove to be less comfortable and provide less than certain outcomes. Our analysis
explores the possibilities for change that might currently be available. This would
appear to involve a consideration of alternative discourses and the reformulation of power
relations and subject positions in health care
Executive summary, overview, conclusions and recommendations
National audienc