We introduce the Lagrangian for a multi-scalar field configuration in a N -dimensional internal space endowed with a constant metric Q ik and generalize the quintom cosmological scenario. We find the energy momentum tensor of the model and show that the set of dual transformations, that preserve the form of the Einstein equations in the Friedmann-Robertson-Walker (FRW) cosmology, is enlarged. We show that the stability of the power law solutions leads to an exponential potential which is invariant under linear transformations in the internal space. Moreover, we obtain the general exact solution of the Einstein-Klein-Gordon equations for that potential. There exist solutions that cross the phantom divide and solutions that blow up at a finite time, exhibiting a superaccelerated behavior and ending in a big rip. We show that the quintom model with a separable potential can be identified with a mixture of several fluids. This framework includes the ΛCDM model, a bouncing model, and a setting sourced by a cosmic string network plus a cosmological constant. The we concentrate on the case where the dimension of the internal quintessence sector Nq exceeds the dimension of the internal phantom sector N ph . For (Nq, N ph ) = (2, 1) the dark energy density derived from the 3-scalar field crosses the phantom divide and its negative component plays the role of the negative part of a classical Dirac Field.

A cosmological model is proposed for the current Universe consisted of non-interacting baryonic matter and interacting dark components. The dark energy and dark matter are coupled through their effective barotropic indexes, which are considered as functions of the ratio between their energy densities. It is investigated two cases where the ratio is asymptotically stable and their parameters are adjusted by considering best fits to Hubble function data. It is shown that the deceleration parameter, the densities parameters, and the luminosity distance have the correct behavior which is expected for a viable present scenario of the Universe.Comment: 6 pages, 8 figure

We investigate a Bianchi type-I (BTI) cosmology with k-essence and find the set of models which dissipate the initial anisotropy. There are cosmological models with extended tachyon fields and k-essence having constant barotropic index. We obtain the conditions leading to a regular bounce of the average geometry and the residual anisotropy on the bounce. For constant potential, we develop purely kinetic k-essence models which are dust dominated in their early stages, dissipate the initial anisotropy and end in a stable de Sitter accelerated expansion scenario. We show that linear k field and polynomial kinetic function models evolve asymptotically to FriedmannRobertson-Walker (FRW) cosmologies. The linear case is compatible with an asymptotic potential interpolating between V l ∝ φ −γ l , in the shear dominated regime, and V l ∝ φ −2 at late time. In the polynomial case, the general solution contains cosmological models with an oscillatory average geometry. For linear k-essence, we find the general solution in the BTI cosmology when the k field is driven by an inverse square potential. This model shares the same geometry as a quintessence field driven by an exponential potential.