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Entropy evolution of universes with initial and final de Sitter eras

J. P. Mimoso, D. Pavůn

Abstract
This brief report studies the behavior of entropy in two recent models of cosmic evolution by J. A. S. Lima, S. Basilakos, and F. E. M. Costa [Phys. Rev. D 86, 103534 (2012)PRVDAQ1550-7998], and J. A. S. Lima, S. Basilakos, and J. SolŠ [arXiv:1209.2802]. Both start with an initial de Sitter expansion, go through the conventional radiation and matter dominated eras to be followed by a final and everlasting de Sitter expansion. In spite of their outward similarities (from the observational viewpoint they are arbitrary close to the conventional Lambda cold dark matter model), they deeply differ in the physics behind them. Our study reveals that in both cases the Universe approaches thermodynamic equilibrium in the last de Sitter era in the sense that the entropy of the apparent horizon plus that of matter and radiation inside it increases and is concave. Accordingly, they are consistent with thermodynamics. Cosmological models that do not approach equilibrium at the last phase of their evolution appear in conflict with the second law of thermodynamics.

Keywords
Cosmology - Dark: energy

Physical Review D
Volume 87, Issue 0473, Page 047302_1
2013 February

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Instituto de Astrof√≠sica e Ci√™ncias do Espa√ßo Universidade do Porto Faculdade de Ciências da Universidade de Lisboa
Fundação para a Ciência e a Tecnologia COMPETE 2020 PORTUGAL 2020 União Europeia