Beyond the perfect fluid hypothesis for dark energy equation of state

Abandoning the perfect fluid hypothesis, we investigate here the possibility that the dark energy equation of state (EoS) $w$ is a nonlinear function of the energy density $\rho$. To this aim, we consider four different EoS describing classical fluids near thermodynamical critical points and discuss the main features of cosmological models made out of dust matter and a dark energy term with the given EoS. Each model is tested against the data on the dimensionless coordinate distance to Type Ia Supernovae and radio galaxies, the shift and the acoustic peak parameters and the positions of the first three peaks in the anisotropy spectrum of the comic microwave background radation. We propose a possible interpretation of each model in the framework of scalar field quintessence determining the shape of the self interaction potential $V(\phi)$ that gives rise to each one of the considered thermodynamical EoS. As a general result, we demonstrate that replacing the perfect fluid EoS with more generar expressions gives both the possibility of successfully solving the problem of cosmic acceleration escaping the resort to phantom models.Comment: 15 pages, 4 figures, accepted for publication on Physical Review

Statistische Uebersicht der wichtigsten Gegenstände des Verkehrs und Verbrauchs im Preußischen Staate und im deutschen Zollverbande

Band 1 : "... in dem Zeitraume von 1831 bis 1836", 1838; Band 2 : "... in dem Zeitraume von 1837 bis 1839. Erste Fortsetzung.", 1842; Band 3 : "Zweite Fortsetzung. Zeitraum von 1840 bis 1842", 1844; Band 4 : "Dritte Fortsetzung. Zeitraum von 1843 bis 1845", 1848; Band 5 : "Vierte Fortsetzung. Zeitraum von 1846 bis 1848", 1851; Band 6 : "Fünfte Fortsetzung. Zeitraum von 1849 bis 1853", 1857