Wormholes and Ringholes in a Dark-Energy Universe

The effects that the present accelerating expansion of the universe has on the size and shape of Lorentzian wormholes and ringholes are considered. It is shown that, quite similarly to how it occurs for inflating wormholes, relative to the initial embedding-space coordinate system, whereas the shape of the considered holes is always preserved with time, their size is driven by the expansion to increase by a factor which is proportional to the scale factor of the universe. In the case that dark energy is phantom energy, which is not excluded by present constraints on the dark-energy equation of state, that size increase with time becomes quite more remarkable, and a rather speculative scenario is here presented where the big rip can be circumvented by future advanced civilizations by utilizing sufficiently grown up wormholes and ringholes as time machines that shortcut the big-rip singularity.Comment: 11 pages, RevTex, to appear in Phys. Rev.

Unified Model for Dark Energy

A new model for the universe filled with a generalized Chaplygin fluid is considered which unitarily describes as a single vacuum entity both a quintessence scalar field and a cosmological constant, so unifying the notion of dark energy. While the evolution of the universe filled with such a fluid does not obviously contradict the present cosmic acceleration, the introduced single dark-energy component, for equations of state with characteristic parameter $\omega\geq -1$, behaves like an usual quintessence fluid with constant equation of state at early high densities, and like a pure cosmological constant at late cosmological times.Comment: 5 pages, some misprints corrected, a comment on the initial equation of state inserted, one reference adde

Chaplygin gas may prevent big trip

This paper deals with the study of the accretion of a generalized Chaplygin gas with equation of state $p=-A/\rho^\alpha$ onto wormholes. We have obtained that when dominant energy condition is violated the size of wormhole increases with the scale factor up to a given plateau. On the regime where the dominant energy condition is satisfied our model predicts a steady decreasing of the wormhole size as generalized Chaplygin gas is accreted. Our main conclusion is that the big trip mechanism is prevented in a large region of the physical parameters of the used model.Comment: 6 pages, no figures, uses Revtex. Several typos corrected. References update