(N+1)-dimensional Lorentzian evolving wormholes supported by polytropic matter

In this paper we study $(N+1)$-dimensional evolving wormholes supported by energy satisfying a polytropic equation of state. The considered evolving wormhole models are described by a constant redshift function and generalizes the standard flat Friedmann-Robertson-Walker spacetime. The polytropic equation of state allows us to consider in $(3+1)$-dimensions generalizations of the phantom energy and the generalized Chaplygin gas sources.Comment: 6 pages, 2 figures, accepted for publication in European Physical Journal

Phantom evolving wormholes with big rip singularities

We investigate a family of inhomogeneous and anisotropic gravitational fields exhibiting a future singularity at a finite value of the proper time. The studied spherically symmetric spacetimes are asymptotically Friedmann-Robertson-Walker at spatial infinity and describe wormhole configurations filled with two matter components: one inhomogeneous and anisotropic fluid and another isotropic and homogeneously distributed fluid, characterized by the supernegative equation of state \omega=p/\rho < -1. In previously constructed wormholes, the notion of the phantom energy was used in a more extended sense than in cosmology, where the phantom energy is considered a homogeneously distributed fluid. Specifically, for some static wormhole geometries the phantom matter was considered as an inhomogeneous and anisotropic fluid, with radial and lateral pressures satisfying the relations $p_{r}/\rho<-1$ and $p_{_l} \neq p_r$, respectively. In this paper we construct phantom evolving wormhole models filled with an isotropic and homogeneous component, described by a barotropic or viscous phantom energy, and ending in a big rip singularity. In two of considered cases the equation of state parameter is constrained to be less than -1, while in the third model the finite-time future singularity may occur for $\omega<-1$, as well as for $-1 < \omega \leq 1$.Comment: 9 pages, 9 figures, accepted for publication in Phys. Rev.

Form invariant transformations between n-- and m-- dimensional flat Friedmann--Robertson--Walker cosmologies

We illustrate how the group of symmetry transformations, which preserve the form of the n--dimensional flat Friedmann--Robertson--Walker cosmologies satisfying Einstein equations, acts in any dimension. This group relates the energy density and the isotropic pressure of the cosmic fluid to the expansion rate. The freedom associated with the dimension of the space time yields assisted inflation even when the energy density of the fluid is a dimensional invariant and enriches the set of duality transformations leading to phantom cosmologies.Comment: Accepted for publication in Iternational Journal of Modern Physics