Extended logotropic fluids as unified dark energy models
  We here study extended classes of logotropic fluids as \textit{unified dark
energy models}. Under the hypothesis of the Anton-Schmidt scenario, we consider
the universe obeying a single fluid whose pressure evolves through a
logarithmic equation of state. This result is in analogy with crystals under
isotropic stresses. Thus, we investigate thermodynamic and dynamical
consequences by integrating the speed of sound to obtain the pressure in terms
of the density, leading to an extended version of the Anton-Schmidt cosmic
fluids. Within this picture, we get significant outcomes expanding the
Anton-Schmidt pressure in the infrared regime. The low-energy case becomes
relevant for the universe to accelerate without any cosmological constant. We
therefore derive the effective representation of our fluid in terms of a
Lagrangian $\mathcal{L}=\mathcal{L}(X)$, depending on the kinetic term $X$
only. We analyze both the relativistic and non-relativistic limits. In the
non-relativistic limit we construct both the Hamiltonian and Lagrangian in
terms of density $\rho$ and scalar field $\vartheta$, whereas in the
relativistic case no analytical expression for the Lagrangian can be found.
Thus, we obtain the potential as a function of $\rho$, under the hypothesis of
irrotational perfect fluid. We demonstrate that the model represents a natural
generalization of \emph{logotropic dark energy models}. Finally, we analyze an
extended class of generalized Chaplygin gas models with one extra parameter
$\beta$. Interestingly, we find that the Lagrangians of this scenario and the
pure logotropic one coincide in the non-relativistic regime.
