A setting constituted by N 3-form fields, without any direct interaction between them, minimally coupled to gravity, is introduced in this paper as a framework to study the early evolution of the universe. We focus particularly on the two 3-forms case. An inflationary scenario is found, emerging from the coupling to gravity. More concretely, the fields coupled in this manner exhibit a complex interaction, mediated by the time derivative of the Hubble parameter. Our investigation is supported by means of a suitable choice of potentials, employing numerical methods and analytical approximations. In more detail, the oscillations on the small field limit become correlated, and one field is intertwined with the other. In this type of solution, a varying sound speed is present, together with the generation of isocurvature perturbations. The mentioned features allow to consider an interesting model, to test against observation. It is subsequently shown how our results are consistent with current CMB data (viz.Planck and BICEP2).

In this paper we consider spherically symmetric general fluids with heat flux, motivated by causal thermodynamics, and give the appropriate set of conditions that define separating shells, defining the divide between expansion and collapse. To do so we add the new requirement that heat flux and its evolution vanish at the separating surface. We extend previous works with a fully nonlinear analysis in the 1 +3 splitting and present gauge-invariant results. The definition of the separating surface is inspired by the conservation of the Misner-Sharp mass and is obtained by generalizing the Tolman-Oppenheimer-Volkoff equilibrium and turnaround conditions. We emphasize the nonlocal character of these conditions as found in previous works and discuss connections to the phenomena of spacetime cracking and thermal peeling.