3 research outputs found
Accelerating Universe and Cosmological Perturbation in the Ghost Condensate
In the simplest Higgs phase of gravity called ghost condensation, an
accelerating universe with a phantom era (w<-1) can be realized without ghost
or any other instabilities. In this paper we show how to reconstruct the
potential in the Higgs sector Lagrangian from a given cosmological history
(H(t), \rho(t)). This in principle allows us to constrain the potential by
geometrical information of the universe such as supernova distance-redshift
relation. We also derive the evolution equation for cosmological perturbations
in the Higgs phase of gravity by employing a systematic low energy expansion.
This formalism is expected to be useful to test the theory by dynamical
information of large scale structure in the universe such as cosmic microwave
background anisotropy, weak gravitational lensing and galaxy clustering.Comment: 30 pages; typos corrected; version accepted for publication in JCA
A Single Scalar Field Model of Dark Energy with Equation of State Crossing -1
In this paper we study the possibility of building models of dark energy with
equation of state across -1 and propose explicitly a model with a single scalar
field which gives rise to an equation of state larger than -1 in the past and
less than -1 at the present time, consistent with the current observations.Comment: 4 pages, 1 figure, the version accepted by JCAP, presentation
improved and references adde
Mimicking Lambda with a spin-two ghost condensate
We propose a simple higher-derivative braneworld gravity model which contains
a stable accelerating branch, in the absence of cosmological constant or
potential, that can be used to describe the late time cosmic acceleration. This
model has similar qualitative features to that of Dvali-Gabadadze-Porrati, such
as the recovery of four-dimensional gravity at subhorizon scales, but unlike
that case, the graviton zero mode is massless and there are no linearized
instabilities. The acceleration rather is driven by bulk gravity in the form of
a spin-two ghost condensate. We show that this model can be consistent with
cosmological bounds and tests of gravity.Comment: references adde