Dark energy from geometrothermodynamics

We investigate a general class of equations of state reproducing the dark energy effects in terms of geometric considerations on thermodynamic interaction. We infer cosmological solutions by combining thermodynamics with contact manifold and Riemannian geometry, showing that the standard ΛCDM model can be treated as a limiting case of a more general approach, providing early time departures as the universe expands. Thus, we interpret the microscopic nature of dark energy through the mathematical formalism of geometrothermodynamics (GTD). In particular, we investigate the thermodynamic nature of a class of cosmological models which reproduce how the universe is currently speeding up. To do so, we aim to describe thermodynamic equilibrium states of the universe through a particular equilibrium space, where the Riemannian metric g becomes a thermodynamical ruler between different states. The particular assumption we made is to consider the metric structure to be invariant under precise Legendre transformations. It turns out that any thermodynamic interaction is determined once the scalar curvature of the equilibrium manifold is known. The consequence of our recipe leads to a class of dark energy equations of state which relates standard pressure to the volume occupied by the fluid itself. In our picture, dark energy is thus determined from constant thermodynamic interaction on the manifold of GTD.