4 research outputs found
Evolution of a Kerr-Newman black hole in a dark energy universe
This paper deals with the study of the accretion of dark energy with equation
of state onto Kerr-Newman black holes. We have obtained that when
the mass and specific angular momentum increase, and that whereas the
specific angular momentum increases up to a given plateau, the mass grows up
unboundedly. On the regime where the dominant energy condition is violated our
model predicts a steady decreasing of mass and angular momentum of black holes
as phantom energy is being accreted. Masses and and angular momenta of all
black holes tend to zero when one approaches the big rip. The results that
cosmic censorship is violated and that the black hole size increases beyond the
universe size itself are discussed in terms of considering the used models as
approximations to a more general descriptions where the metric is
time-dependent.Comment: 11 figures added. Some explanations extended. E-mails updated.
References updated. Conclusions unchanged. Accepted in Gravitation &
Cosmolog
Two Loop Scalar Self-Mass during Inflation
We work in the locally de Sitter background of an inflating universe and
consider a massless, minimally coupled scalar with a quartic self-interaction.
We use dimensional regularization to compute the fully renormalized scalar
self-mass-squared at one and two loop order for a state which is released in
Bunch-Davies vacuum at t=0. Although the field strength and coupling constant
renormalizations are identical to those of lfat space, the geometry induces a
non-zero mass renormalization. The finite part also shows a sort of growing
mass that competes with the classical force in eventually turning off this
system's super-acceleration.Comment: 31 pages, 5 figures, revtex4, revised for publication with extended
list of reference
Coupled dark energy: Towards a general description of the dynamics
In dark energy models of scalar-field coupled to a barotropic perfect fluid,
the existence of cosmological scaling solutions restricts the Lagrangian of the
field \vp to p=X g(Xe^{\lambda \vp}), where X=-g^{\mu\nu} \partial_\mu \vp
\partial_\nu \vp /2, is a constant and is an arbitrary function.
We derive general evolution equations in an autonomous form for this Lagrangian
and investigate the stability of fixed points for several different dark energy
models--(i) ordinary (phantom) field, (ii) dilatonic ghost condensate, and
(iii) (phantom) tachyon. We find the existence of scalar-field dominant fixed
points (\Omega_\vp=1) with an accelerated expansion in all models
irrespective of the presence of the coupling between dark energy and dark
matter. These fixed points are always classically stable for a phantom field,
implying that the universe is eventually dominated by the energy density of a
scalar field if phantom is responsible for dark energy. When the equation of
state w_\vp for the field \vp is larger than -1, we find that scaling
solutions are stable if the scalar-field dominant solution is unstable, and
vice versa. Therefore in this case the final attractor is either a scaling
solution with constant \Omega_\vp satisfying 0<\Omega_\vp<1 or a
scalar-field dominant solution with \Omega_\vp=1.Comment: 21 pages, 5 figures; minor clarifications added, typos corrected and
references updated; final version to appear in JCA
Cosmological Evolution of Interacting Phantom Energy with Dark Matter
We investigate the cosmological evolution of an interacting phantom energy
model in which the phantom field has interaction with the dark matter. We
discuss the existence and stability of scaling solutions for two types of
specific interactions. One is motivated by the conformal transformation in
string theory and the other is motivated by analogy with dissipation. In the
former case, there exist no scaling solutions. In the latter case, there exist
stable scaling solutions, which may give a phenomenological solution of the
coincidence problem. Furthermore, the universe either accelerates forever or
ends with a singularity, which is determined by not only the model parameters
but also the initial velocity of the phantom field.Comment: 7 pages, 11 figures, RevTe