Abstract
We study extended classes of logotropic fluids as unified dark energy models. Under the hypothesis of the Anton–Schmidt scenario, we consider a universe obeying a single fluid model with a logarithmic equation of state. We investigate the thermodynamic and dynamical consequences of an extended version of the Anton–Schmidt cosmic fluids. Specifically, we expand the Anton–Schmidt pressure in the infrared regime. The low-energy case becomes relevant for the universe as regards acceleration without any cosmological constant. We therefore derive the effective representation of our fluid in terms of a Lagrangian depending on the kinetic term only. We analyze both the relativistic and the non-relativistic limits. In the non-relativistic limit we construct both the Hamiltonian and the 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 an irrotational perfect fluid. We demonstrate that the model represents a natural generalization of 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.
Highlights
ΛCDM model provide unexpectedly small constraints over Λ, disagreeing with theoretical predictions [3]
We study extended classes of logotropic fluids as unified dark energy models
We analyze an extended class of generalized Chaplygin gas models with one extra parameter β
Summary
ΛCDM model provide unexpectedly small constraints over Λ, disagreeing with theoretical predictions [3]. This observational evidence jeopardizes our theoretical understanding on the standard paradigm [4], leading to a severe cosmological constant problem Possibilities to circumvent this issue lie in abandoning Λ in favor of a varying quintessence field [5,6] or of a dark energy contribution. A likely more successful unified dark fluid would overcome such caveats with a weakly increasing pressure P in terms of the density ρ To this end, a logotropic version of the equation of state has recently been proposed by [14] as a natural and robust candidate for unifying dark energy and dark matter. We have promising scenarios, logotropic dark energy is not directly associated to a particular constituent, leaving open the challenge of understanding which particles the logotropic fluid is composed of In support of this fact, it has been shown that logotropic versions of dark energy fall inside a more general class based on Anton–Schmidt fluids [16,17].
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