On the accretion of phantom energy onto wormholes

By using a properly generalized accretion formalism it is argued that the accretion of phantom energy onto a wormhole does not make the size of the wormhole throat to comovingly scale with the scale factor of the universe, but instead induces an increase of that size so big that the wormhole can engulf the universe itself before it reaches the big rip singularity, at least relative to an asymptotic observer.Comment: 4 pages, LaTex, to appear in Phys. Lett.

The entangled accelerating universe

Using the known result that the nucleation of baby universes in correlated pairs is equivalent to spacetime squeezing, we show in this letter that there exists a T-duality symmetry between two-dimensional warp drives, which are physically expressible as localized de Sitter little universes, and two dimensional Tolman-Hawking and Gidding-Strominger baby universes respectively correlated in pairs, so that the creation of warp drives is also equivalent to spacetime squeezing. Perhaps more importantly, it has been also seen that the nucleation of warp drives entails a violation of the Bell's inequalities, and hence the phenomena of quantum entanglement, complementarity and wave function collapse. These results are generalized to the case of any dynamically accelerating universe filled with dark or phantom energy whose creation is also physically equivalent to spacetime squeezing and to the violation of the Bell's inequalities, so that the universe we are living in should be governed by essential sharp quantum theory laws and must be a quantum entangled system

Cosmological models from quintessence

A generalized quintessence model is presented which corresponds to a richer vacuum structure that, in addition to a time-dependent, slowly varying scalar field, contains a varying cosmological term. From first principles we determine a number of scalar-field potentials that satisfy the constraints imposed by the field equations and conservation laws, both in the conventional and generalized quintessence models. In addition to the inverse-power law solutions, these potentials are given in terms of hyperbolic functions or the 12 Jacobian elliptic functions, and are all related to the luminosity distance by means of an integral equation. Integration of this equation for the different solutions leads to a large family of cosmological models characterized by luminosity distance-redshift relations. Out of such models, only four appear to be able to predict a required accelerating universe conforming to observations on supernova type Ia, at large or moderate redshifts. ©2000 The American Physical Society.This research was supported by DGICYT under Research Project No. PB97-1218.Peer Reviewe

Dark energy and supermassive black holes

This paper deals with a cosmological model in which the universe is filled with tachyon dark energy in order to describe current and future accelerating expansion. We obtain that the simplest condition for the regime of phantom energy to occur in this scenario is that the scalar field be Wick rotated to imaginary values which correspond to an axionic field classically. By introducing analytical expressions for the scale factor or the Hubble parameter that satisfy all constraint equations of the used models we show that such models describe universes which may develop a big rip singularity in the finite future. It is argued that, contrary to a recent claim, the entropy for a universe filled with dark energy is definite positive even on the phantom regime where the universe would instead acquire a negative temperature. It is also seen that, whichever the fate of the tachyonic accelerating universe, it will be stable to any fluctuations of the scalar field, and that since the considered models have all an imaginary sound speed, any overdense regions will undergo an accelerated collapse leading rapidly to formation of giant black holes. Finally the conjecture is advanced that these black holes may be the supermassive black holes that most galaxies harbor at their center. © 2004 The American Physical Society.The author thanks Carmen L. Sigu¨enza for useful discussions and Yun-Song Piao, Fabio Finelli, J. S. Alcaniz, and J. A. S. Lima for valuable correspondence. This work was supported by DGICYT under Research Project No. BMF2002-03758.Peer Reviewe

Quintessence in brane cosmology

In order to reconcile the non conventional character of brane cosmology with standard Friedmann cosmology, we introduce in this paper a slowly-varying quintessence scalar field in the brane and analyse the cosmological solutions corresponding to some equations of state for the scalar field. Different compensation mechanisms between the cosmological constant in the bulk and the constant tension resulting from the combined effect of ordinary matter and the quintessence scalar field are derived or assumed. It has been checked that the Randall-Sundrum approach is not necessarily the best procedure to reconcile brane and standard cosmologies, and that there exists at least another compensating mechanism that reproduces a rather conventional behaviour for an accelerating universe. (C) 2000 Elsevier Science B.V.This work was supported by DGICYT under Research Project No. PB97-1218.Peer Reviewe

Tensorial perturbations in the bulk of inflating brane worlds

In this paper we consider the stability of some inflating brane-world models in quantum cosmology. It is shown that whereas the singular model based on the construction of inflating branes from Euclidean five-dimensional anti-de Sitter space is unstable to tensorial cosmological perturbations in the bulk, the nonsingular model which uses a five-dimensional asymptotically anti-de Sitter wormhole to construct the inflating branes is stable to these perturbations.Comment: 4 pages, RevTex, to appear in Phys. Rev.

A dark energy multiverse

We present cosmic solutions corresponding to universes filled with dark and phantom energy, all having a negative cosmological constant. All such solutions contain infinite singularities, successively and equally distributed along time, which can be either big bang/crunchs or big rips singularities. Classicaly these solutions can be regarded as associated with multiverse scenarios, being those corresponding to phantom energy that may describe the current accelerating universe

On the Tolman-Hawking wormhole

The Tolman-Hawking wormhole a=(R2+2)12 can be obtained as a solution of the Einstein equations with a conformally coupled scalar field. However, this procedure gives rise to negative values of the effective gravitational constant. Working in a pure-gravity minisuperspace isotropic model, I propose a much simpler method to obtain this instanton based on the introduction of a cutoff in the scale factor which is equivalent to introducing a three-sphere with minimum constant radius in the Euclidean metric. The resulting wormhole model no longer has any negative effective gravitational constant. © 1989 The American Physical Society.Peer Reviewe