3 research outputs found
Static Configurations of Dark Energy and Dark Matter
We study static configurations of dark matter coupled to a scalar field
responsible for the dark energy of the Universe. The dark matter is modelled as
a Fermi gas within the Thomas-Fermi approximation. The mass of the dark matter
particles is a function of the scalar field. We analyze the profile of the dark
matter halos in galaxies. In this case our framework is equivalent to the model
of the isothermal sphere. In the presence of a scalar field, the velocity of a
massive object orbiting the galaxy is not of the order of the typical velocity
of the dark matter particles, as in the conventional picture. Instead, it is
reduced by a factor that quantifies the dependence of the dark matter mass on
the scalar field. This has implications for dark matter searches. We derive new
solutions of the Einstein equations which describe compact objects composed of
dark matter. Depending on the scale of the dark matter mass, the size of these
objects can vary between microscopic scales and cosmological distances. We
determine the mass to radius relation and discuss the similarities with
conventional neutron stars and exotic astrophysical objects.Comment: 23 pages, 3 figures, minor additions to the tex
Natural Phantom Dark Energy, Wiggling Hubble Parameter and Direct Data
Recent direct data indicate that the parameter may wiggle with
respect to . On the other hand the luminosity distance data of supernovae
flatten the wiggles of because of integration effect. It is expected
that the fitting results can be very different in a model permitting a wiggling
because the data of supernovae is highly degenerated to such a model. As
an example the natural phantom dark energy is investigated in this paper. The
dynamical property of this model is studied. The model is fitted by the direct
data set and the SNLS data set, respectively. And the results are quite
different, as expected. The quantum stability of this model is also shortly
discussed. We find it is a viable model if we treat it as an effective theory
truncated by an upperbound.Comment: 14 pages, 2 figures, discussions on the stability added, conclusions
not change
The Accelerated Acceleration of the Universe
We present a simple mechanism which can mimic dark energy with an equation of
state w < -1 as deduced from the supernova data. We imagine that the universe
is accelerating under the control of a quintessence field, which is moving up a
very gently sloping potential. As a result, the potential energy and hence the
acceleration increases at lower redshifts. Fitting this behavior with a dark
energy model with constant w would require w<-1. In fact we find that the
choice of parameters which improves the fit to the SNe mimics w = -1.4 at low
redshifts. Running up the potential in fact provides the best fit to the SN
data for a generic quintessence model. However, unlike models with phantoms,
our model does not have negative energies or negative norm states. Future
searches for supernovae at low redshifts 0.1 < z < 0.5 and at high redshifts
z>1 may be a useful probe of our proposal.Comment: 14 pages, 5 figure