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Entropy 2017, 19(10), 551; https://doi.org/10.3390/e19100551

Cosmographic Thermodynamics of Dark Energy

1,2,3,4,5
1
Department of Mathematics and Applied Mathematics, University of Cape Town, Rondebosch 7701, Cape Town, South Africa
2
Astrophysics, Cosmology and Gravity Centre (ACGC), University of Cape Town, Rondebosch 7701, Cape Town, South Africa
3
School of Science and Technology, University of Camerino, I-62032 Camerino, Italy
4
Dipartimento di Fisica, Università di Napoli “Federico II”, Via Cinthia, I-80126 Napoli, Italy
5
Istituto Nazionale di Fisica Nucleare (INFN), Sez. di Napoli, Via Cinthia 9, I-80126 Napoli, Italy
Received: 4 August 2017 / Revised: 2 October 2017 / Accepted: 9 October 2017 / Published: 19 October 2017
(This article belongs to the Special Issue Dark Energy)
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Abstract

Dark energy’s thermodynamics is here revised giving particular attention to the role played by specific heats and entropy in a flat Friedmann-Robertson-Walker universe. Under the hypothesis of adiabatic heat exchanges, we rewrite the specific heats through cosmographic, model-independent quantities and we trace their evolutions in terms of z. We demonstrate that dark energy may be modeled as perfect gas, only as the Mayer relation is preserved. In particular, we find that the Mayer relation holds if j q > 1 2 . The former result turns out to be general so that, even at the transition time, the jerk parameter j cannot violate the condition: j t r > 1 2 . This outcome rules out those models which predict opposite cases, whereas it turns out to be compatible with the concordance paradigm. We thus compare our bounds with the Λ CDM model, highlighting that a constant dark energy term seems to be compatible with the so-obtained specific heat thermodynamics, after a precise redshift domain. In our treatment, we show the degeneracy between unified dark energy models with zero sound speed and the concordance paradigm. Under this scheme, we suggest that the cosmological constant may be viewed as an effective approach to dark energy either at small or high redshift domains. Last but not least, we discuss how to reconstruct dark energy’s entropy from specific heats and we finally compute both entropy and specific heats into the luminosity distance d L , in order to fix constraints over them through cosmic data. View Full-Text
Keywords: dark energy; thermodynamics dark energy; thermodynamics
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Luongo, O. Cosmographic Thermodynamics of Dark Energy. Entropy 2017, 19, 551.

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